Overhaul of GnuTLS code.

GnuTLS code re-done, using cut&paste for preservation where appropriate. Stop using deprecated APIs. Stop hard-coding lists of ciphers. Use gnutls_priority_init() instead. Turns tls_require_ciphers into a string in the GnuTLS case, not just OpenSSL case. Deprecate three gnutls_require_* options; now ignored but not errors. (No warnings yet). Added TLS SNI support. Made the channel binding integration theoretically actually work. I had it guarded by an #ifdef but the value used was an enum instead. Oops. Fixed. New code much more amenable to future work permitting TLS in callouts. DH param sizes now chosen by GnuTLS maintainers, we use "normal"; that's suddenly a lot more bits, so the saved filename was changed too. (GNUTLS_SEC_PARAM_NORMAL). DH param setup only done for servers now, since clients don't need/use it. GnuTLS a lot more robust to library negotiation using stuff we don't support, error-ing out quickly for other authentication systems (PGP, etc). Renamed pseudo_random_number() to vaguely_random_number() which makes the nature clearer. GnuTLS now provides a vaguely_random_number() implementation, to match OpenSSL. Pull in <inttypes.h> to make the recent arithmetic changes compile on MacOS. Nuke test 2011 which related to the gnutls_require_* options now non-functional.
author: Phil Pennock <pdp@exim.org> 2012-05-16 12:15:26 -0400
committer: Phil Pennock <pdp@exim.org> 2012-05-16 12:15:26 -0400
commit: 17c761988f30054827a9951761d93ffeeaad0cb7 (patch)
tree: 10d8b048f0c7059c28a2ad5e4257a19e46d47267 /src
parent: f675bf30a2ce6242cfc7c3e3997ec5d68a1fca7a (diff)
21 files changed, 1170 insertions, 793 deletions
diff --git a/src/OS/os.h-Darwin b/src/OS/os.h-Darwin
index 888b9c759..af06bdcbc 100644
--- a/src/OS/os.h-Darwin
+++ b/src/OS/os.h-Darwin
@@ -35,4 +35,8 @@ updating Exim to use the newer interface. */
 /* It's not .so for dynamic libraries on Darwin. */
 #define DYNLIB_FN_EXT "dylib"
 
+/* We currently need some assistance getting OFF_T_FMT correct on MacOS */
+#define OFF_T_FMT "%llu"
+#define LONGLONG_T long int
+
 /* End */
diff --git a/src/README.UPDATING b/src/README.UPDATING
index 0d729a384..81e767efe 100644
--- a/src/README.UPDATING
+++ b/src/README.UPDATING
@@ -77,6 +77,30 @@ Exim version 4.78
    new option, you can safely force it off before upgrading, to decouple
    configuration changes from the binary upgrade while remaining RFC compliant.
 
+ * The GnuTLS support has been mostly rewritten, to use 2.12.x APIs.  As part
+   of this, these three options are no longer supported:
+
+     gnutls_require_kx
+     gnutls_require_mac
+     gnutls_require_protocols
+
+   Their functionality is entirely subsumed into tls_require_ciphers, which is
+   no longer parsed apart by Exim but is instead given to
+   gnutls_priority_init(3), which is no longer an Exim list.  See:
+
+     http://www.gnu.org/software/gnutls/manual/html_node/Priority-Strings.html
+
+   for fuller documentation of the strings parsed.  The three gnutls_require_*
+   options are still parsed by Exim and, for this release, silently ignored.
+   A future release will add warnings, before a later still release removes
+   parsing entirely and the presence of the options will be a configuration
+   error.
+
+   This rewrite means that Exim will continue to build against GnuTLS in the
+   future, brings Exim closer to other GnuTLS applications and lets us add
+   support for SNI and other features more readily.  We regret that it wasn't
+   feasible to retain the three dropped options.
+
 
 Exim version 4.77
 -----------------
diff --git a/src/exim_monitor/em_globals.c b/src/exim_monitor/em_globals.c
index 720549382..e74118c45 100644
--- a/src/exim_monitor/em_globals.c
+++ b/src/exim_monitor/em_globals.c
@@ -214,7 +214,7 @@ BOOL    timestamps_utc         = FALSE;
 BOOL    tls_certificate_verified = FALSE;
 uschar *tls_cipher             = NULL;
 uschar *tls_peerdn             = NULL;
-#ifndef USE_GNUTLS
+#ifdef SUPPORT_TLS
 uschar *tls_sni                = NULL;
 #endif
 
diff --git a/src/src/buildconfig.c b/src/src/buildconfig.c
index 64902a1ee..1eaf2f505 100644
--- a/src/src/buildconfig.c
+++ b/src/src/buildconfig.c
@@ -103,6 +103,7 @@ off_t test_off_t = 0;
 time_t test_time_t = 0;
 #if ! (__STDC_VERSION__ >= 199901L)
 size_t test_size_t = 0;
+ssize_t test_ssize_t = 0;
 unsigned long test_ulong_t = 0L;
 #endif
 long test_long_t = 0;
@@ -179,15 +180,22 @@ else
 fprintf(new, "#endif\n\n");
 
 /* And for sizeof() results, size_t, which should with C99 be just %zu, deal
-with C99 not being ubiquitous yet.  Unfortunately. */
+with C99 not being ubiquitous yet.  Unfortunately.  Assume ssize_t is same
+size as size_t on C99; if someone comes up with a version where it's not, fix
+it then. */
 
 #if __STDC_VERSION__ >= 199901L
 fprintf(new, "#define SIZE_T_FMT  \"%%zu\"\n");
+fprintf(new, "#define SSIZE_T_FMT  \"%%zd\"\n");
 #else
 if (sizeof(test_size_t) > sizeof (test_ulong_t))
   fprintf(new, "#define SIZE_T_FMT  \"%%llu\"\n");
 else
   fprintf(new, "#define SIZE_T_FMT  \"%%lu\"\n");
+if (sizeof(test_ssize_t) > sizeof(test_long_t))
+  fprintf(new, "#define SSIZE_T_FMT  \"%%lld\"\n");
+else
+  fprintf(new, "#define SSIZE_T_FMT  \"%%ld\"\n");
 #endif
 
 /* Now search the makefile for certain settings */
diff --git a/src/src/exim.h b/src/src/exim.h
index e6e72facc..49f52474a 100644
--- a/src/src/exim.h
+++ b/src/src/exim.h
@@ -77,6 +77,10 @@ making unique names. */
 #include <limits.h>
 #endif
 
+/* C99 integer types, figure out how to undo this if needed for older systems */
+
+#include <inttypes.h>
+
 /* Just in case some aged system doesn't define them... */
 
 #ifndef INT_MAX
diff --git a/src/src/expand.c b/src/src/expand.c
index dcc813801..2fc953aec 100644
--- a/src/src/expand.c
+++ b/src/src/expand.c
@@ -615,7 +615,7 @@ static var_entry var_table[] = {
   { "tls_certificate_verified", vtype_int,    &tls_certificate_verified },
   { "tls_cipher",          vtype_stringptr,   &tls_cipher },
   { "tls_peerdn",          vtype_stringptr,   &tls_peerdn },
-#if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
+#ifdef SUPPORT_TLS
   { "tls_sni",             vtype_stringptr,   &tls_sni },
 #endif
   { "tod_bsdinbox",        vtype_todbsdin,    NULL },
@@ -776,6 +776,7 @@ return rc;
 
 
 
+
 /*************************************************
 *        Pseudo-random number generation         *
 *************************************************/
@@ -788,19 +789,23 @@ weirdness they'll twist this into.  The result should ideally handle fork().
 However, if we're stuck unable to provide this, then we'll fall back to
 appallingly bad randomness.
 
-If SUPPORT_TLS is defined and OpenSSL is used, then this will not be used.
-The GNUTLS randomness functions found do not seem amenable to extracting
-random numbers outside of a TLS context.  Any volunteers?
+If SUPPORT_TLS is defined then this will not be used except as an emergency
+fallback.
 
 Arguments:
   max       range maximum
 Returns     a random number in range [0, max-1]
 */
 
-#if !defined(SUPPORT_TLS) || defined(USE_GNUTLS)
+#ifdef SUPPORT_TLS
+# define vaguely_random_number vaguely_random_number_fallback
+#endif
 int
-pseudo_random_number(int max)
+vaguely_random_number(int max)
 {
+#ifdef SUPPORT_TLS
+# undef vaguely_random_number
+#endif
   static pid_t pid = 0;
   pid_t p2;
 #if defined(HAVE_SRANDOM) && !defined(HAVE_SRANDOMDEV)
@@ -843,7 +848,8 @@ pseudo_random_number(int max)
 #endif
 }
 
-#endif
+
+
 
 /*************************************************
 *             Pick out a name from a string      *
@@ -5914,7 +5920,7 @@ while (*s != 0)
         continue;
         }
 
-      /* pseudo-random number less than N */
+      /* vaguely random number less than N */
 
       case EOP_RANDINT:
         {
@@ -5924,7 +5930,7 @@ while (*s != 0)
         max = expand_string_integer(sub, TRUE);
         if (expand_string_message != NULL)
           goto EXPAND_FAILED;
-        s = string_sprintf("%d", pseudo_random_number((int)max));
+        s = string_sprintf("%d", vaguely_random_number((int)max));
         yield = string_cat(yield, &size, &ptr, s, Ustrlen(s));
         continue;
         }
diff --git a/src/src/functions.h b/src/src/functions.h
index 8986f3a49..557b7e72a 100644
--- a/src/src/functions.h
+++ b/src/src/functions.h
@@ -23,13 +23,13 @@ extern uschar *init_perl(uschar *);
 #ifdef SUPPORT_TLS
 extern int     tls_client_start(int, host_item *, address_item *, uschar *,
                  uschar *, uschar *, uschar *, uschar *, uschar *, uschar *,
-                 uschar *, uschar *, uschar *, int);
+                 int);
 extern void    tls_close(BOOL);
 extern int     tls_feof(void);
 extern int     tls_ferror(void);
 extern int     tls_getc(void);
 extern int     tls_read(uschar *, size_t);
-extern int     tls_server_start(uschar *, uschar *, uschar *, uschar *);
+extern int     tls_server_start(const uschar *);
 extern BOOL    tls_smtp_buffered(void);
 extern int     tls_ungetc(int);
 extern int     tls_write(const uschar *, size_t);
@@ -199,7 +199,10 @@ extern uschar *parse_fix_phrase(uschar *, int, uschar *, int);
 extern uschar *parse_message_id(uschar *, uschar **, uschar **);
 extern uschar *parse_quote_2047(uschar *, int, uschar *, uschar *, int, BOOL);
 extern uschar *parse_date_time(uschar *str, time_t *t);
-extern int     pseudo_random_number(int);
+extern int     vaguely_random_number(int);
+#ifdef SUPPORT_TLS
+extern int     vaguely_random_number_fallback(int);
+#endif
 
 extern BOOL    queue_action(uschar *, int, uschar **, int, int);
 extern void    queue_check_only(void);
@@ -379,4 +382,6 @@ extern BOOL    verify_sender(int *, uschar **);
 extern BOOL    verify_sender_preliminary(int *, uschar **);
 extern void    version_init(void);
 
+extern ssize_t write_to_fd_buf(int, const uschar *, size_t);
+
 /* End of functions.h */
diff --git a/src/src/globals.c b/src/src/globals.c
index b68544e54..d341ceb4a 100644
--- a/src/src/globals.c
+++ b/src/src/globals.c
@@ -116,9 +116,7 @@ BOOL    tls_offered            = FALSE;
 uschar *tls_privatekey         = NULL;
 BOOL    tls_remember_esmtp     = FALSE;
 uschar *tls_require_ciphers    = NULL;
-#ifndef USE_GNUTLS
 uschar *tls_sni                = NULL;
-#endif
 uschar *tls_try_verify_hosts   = NULL;
 uschar *tls_verify_certificates= NULL;
 uschar *tls_verify_hosts       = NULL;
diff --git a/src/src/globals.h b/src/src/globals.h
index d267a52b7..37b0f6cf0 100644
--- a/src/src/globals.h
+++ b/src/src/globals.h
@@ -98,9 +98,7 @@ extern BOOL    tls_offered;            /* Server offered TLS */
 extern uschar *tls_privatekey;         /* Private key file */
 extern BOOL    tls_remember_esmtp;     /* For YAEB */
 extern uschar *tls_require_ciphers;    /* So some can be avoided */
-#ifndef USE_GNUTLS
 extern uschar *tls_sni;                /* Server Name Indication */
-#endif
 extern uschar *tls_try_verify_hosts;   /* Optional client verification */
 extern uschar *tls_verify_certificates;/* Path for certificates to check */
 extern uschar *tls_verify_hosts;       /* Mandatory client verification */
diff --git a/src/src/host.c b/src/src/host.c
index 0571772cb..c45c2d77b 100644
--- a/src/src/host.c
+++ b/src/src/host.c
@@ -68,7 +68,7 @@ sprintf(addr, "%d.%d.%d.%d",
 very good for the uses to which it is put. When running the regression tests,
 start with a fixed seed.
 
-If you need better, see pseudo_random_number() which is potentially stronger,
+If you need better, see vaguely_random_number() which is potentially stronger,
 if a crypto library is available, but might end up just calling this instead.
 
 Arguments:
diff --git a/src/src/log.c b/src/src/log.c
index 75285c136..0ba4e638b 100644
--- a/src/src/log.c
+++ b/src/src/log.c
@@ -528,11 +528,11 @@ Returns:
   length actually written, persisting an errno from write()
 */
 ssize_t
-write_to_fd_buf(int fd, uschar *buf, size_t length)
+write_to_fd_buf(int fd, const uschar *buf, size_t length)
 {
 ssize_t wrote;
 size_t total_written = 0;
-uschar *p = buf;
+const uschar *p = buf;
 size_t left = length;
 
 while (1)
diff --git a/src/src/malware.c b/src/src/malware.c
index 864564ffc..79e2e3827 100644
--- a/src/src/malware.c
+++ b/src/src/malware.c
@@ -115,7 +115,7 @@ malware_in_file(uschar *eml_filename) {
   /* spool_mbox() assumes various parameters exist, when creating
   the relevant directory and the email within */
   (void) string_format(message_id_buf, sizeof(message_id_buf),
-      "dummy-%d", pseudo_random_number(INT_MAX));
+      "dummy-%d", vaguely_random_number(INT_MAX));
   message_id = message_id_buf;
   sender_address = US"malware-sender@example.net";
   return_path = US"";
diff --git a/src/src/readconf.c b/src/src/readconf.c
index b35811e48..cdd32be58 100644
--- a/src/src/readconf.c
+++ b/src/src/readconf.c
@@ -235,6 +235,7 @@ static optionlist optionlist_config[] = {
   { "gecos_pattern",            opt_stringptr,   &gecos_pattern },
 #ifdef SUPPORT_TLS
   { "gnutls_compat_mode",       opt_bool,        &gnutls_compat_mode },
+  /* These three gnutls_require_* options stopped working in Exim 4.78 */
   { "gnutls_require_kx",        opt_stringptr,   &gnutls_require_kx },
   { "gnutls_require_mac",       opt_stringptr,   &gnutls_require_mac },
   { "gnutls_require_protocols", opt_stringptr,   &gnutls_require_proto },
diff --git a/src/src/receive.c b/src/src/receive.c
index aaaf64ce6..b3b06e867 100644
--- a/src/src/receive.c
+++ b/src/src/receive.c
@@ -3488,12 +3488,10 @@ if ((log_extra_selector & LX_tls_certificate_verified) != 0 &&
 if ((log_extra_selector & LX_tls_peerdn) != 0 && tls_peerdn != NULL)
   s = string_append(s, &size, &sptr, 3, US" DN=\"",
     string_printing(tls_peerdn), US"\"");
-#ifndef USE_GNUTLS
 if ((log_extra_selector & LX_tls_sni) != 0 && tls_sni != NULL)
   s = string_append(s, &size, &sptr, 3, US" SNI=\"",
     string_printing(tls_sni), US"\"");
 #endif
-#endif
 
 if (sender_host_authenticated != NULL)
   {
diff --git a/src/src/smtp_in.c b/src/src/smtp_in.c
index d1c10f00f..5d241d960 100644
--- a/src/src/smtp_in.c
+++ b/src/src/smtp_in.c
@@ -841,12 +841,10 @@ if ((log_extra_selector & LX_tls_certificate_verified) != 0 &&
 if ((log_extra_selector & LX_tls_peerdn) != 0 && tls_peerdn != NULL)
   s = string_append(s, &size, &ptr, 3, US" DN=\"",
     string_printing(tls_peerdn), US"\"");
-#ifndef USE_GNUTLS
 if ((log_extra_selector & LX_tls_sni) != 0 && tls_sni != NULL)
   s = string_append(s, &size, &ptr, 3, US" SNI=\"",
     string_printing(tls_sni), US"\"");
 #endif
-#endif
 
 sep = (smtp_connection_had[SMTP_HBUFF_SIZE-1] != SCH_NONE)?
   US" C=..." : US" C=";
@@ -1676,8 +1674,7 @@ if (!sender_host_unknown)
 
   #ifdef SUPPORT_TLS
   if (tls_on_connect &&
-      tls_server_start(tls_require_ciphers,
-        gnutls_require_mac, gnutls_require_kx, gnutls_require_proto) != OK)
+      tls_server_start(tls_require_ciphers) != OK)
     return FALSE;
   #endif
 
@@ -3893,8 +3890,7 @@ while (done <= 0)
     We must allow for an extra EHLO command and an extra AUTH command after
     STARTTLS that don't add to the nonmail command count. */
 
-    if ((rc = tls_server_start(tls_require_ciphers, gnutls_require_mac,
-           gnutls_require_kx, gnutls_require_proto)) == OK)
+    if ((rc = tls_server_start(tls_require_ciphers)) == OK)
       {
       if (!tls_remember_esmtp)
         helo_seen = esmtp = auth_advertised = pipelining_advertised = FALSE;
diff --git a/src/src/spool_in.c b/src/src/spool_in.c
index bdc3903c0..f6aa18c34 100644
--- a/src/src/spool_in.c
+++ b/src/src/spool_in.c
@@ -286,10 +286,8 @@ dkim_collect_input = FALSE;
 tls_certificate_verified = FALSE;
 tls_cipher = NULL;
 tls_peerdn = NULL;
-#ifndef USE_GNUTLS
 tls_sni = NULL;
 #endif
-#endif
 
 #ifdef WITH_CONTENT_SCAN
 spam_score_int = NULL;
@@ -552,10 +550,8 @@ for (;;)
       tls_cipher = string_copy(big_buffer + 12);
     else if (Ustrncmp(p, "ls_peerdn", 9) == 0)
       tls_peerdn = string_unprinting(string_copy(big_buffer + 12));
-    #ifndef USE_GNUTLS
     else if (Ustrncmp(p, "ls_sni", 6) == 0)
       tls_sni = string_unprinting(string_copy(big_buffer + 9));
-    #endif
     break;
     #endif
 
diff --git a/src/src/spool_out.c b/src/src/spool_out.c
index fa4f1b6e2..0d32fd6ca 100644
--- a/src/src/spool_out.c
+++ b/src/src/spool_out.c
@@ -229,10 +229,8 @@ if (bmi_verdicts != NULL) fprintf(f, "-bmi_verdicts %s\n", bmi_verdicts);
 if (tls_certificate_verified) fprintf(f, "-tls_certificate_verified\n");
 if (tls_cipher != NULL) fprintf(f, "-tls_cipher %s\n", tls_cipher);
 if (tls_peerdn != NULL) fprintf(f, "-tls_peerdn %s\n", string_printing(tls_peerdn));
-#ifndef USE_GNUTLS
 if (tls_sni != NULL) fprintf(f, "-tls_sni %s\n", string_printing(tls_sni));
 #endif
-#endif
 
 /* To complete the envelope, write out the tree of non-recipients, followed by
 the list of recipients. These won't be disjoint the first time, when no
diff --git a/src/src/tls-gnu.c b/src/src/tls-gnu.c
index 7e87dded0..f0e391f97 100644
--- a/src/src/tls-gnu.c
+++ b/src/src/tls-gnu.c
@@ -2,178 +2,178 @@
 *     Exim - an Internet mail transport agent    *
 *************************************************/
 
-/* Copyright (c) University of Cambridge 1995 - 2009 */
+/* Copyright (c) University of Cambridge 1995 - 2012 */
 /* See the file NOTICE for conditions of use and distribution. */
 
-/* This module provides TLS (aka SSL) support for Exim using the GnuTLS
-library. It is #included into tls.c when that library is used. The code herein
-is based on a patch that was contributed by Nikos Mavroyanopoulos.
+/* Copyright (c) Phil Pennock 2012 */
 
-No cryptographic code is included in Exim. All this module does is to call
-functions from the GnuTLS library. */
+/* This file provides TLS/SSL support for Exim using the GnuTLS library,
+one of the available supported implementations.  This file is #included into
+tls.c when USE_GNUTLS has been set.
 
-/* Note: This appears to be using an old API from compat.h; it is likely that
-someone familiary with GnuTLS programming could rework a lot of this to a
-modern API and perhaps remove the explicit knowledge of crypto algorithms from
-Exim.  Such a re-work would be most welcome and we'd sacrifice support for
-older GnuTLS releases without too many qualms -- maturity and experience
-in crypto libraries tends to improve their robustness against attack.
-Frankly, if you maintain it, you decide what's supported and what isn't. */
+The code herein is a revamp of GnuTLS integration using the current APIs; the
+original tls-gnu.c was based on a patch which was contributed by Nikos
+Mavroyanopoulos.  The revamp is partially a rewrite, partially cut&paste as
+appropriate.
 
-/* Heading stuff for GnuTLS */
+APIs current as of GnuTLS 2.12.18; note that the GnuTLS manual is for GnuTLS 3,
+which is not widely deployed by OS vendors.  Will note issues below, which may
+assist in updating the code in the future.  Another sources of hints is
+mod_gnutls for Apache (SNI callback registration and handling).
 
-#include <gnutls/gnutls.h>
-#include <gnutls/x509.h>
+Keeping client and server variables more split than before and is currently
+the norm, in anticipation of TLS in ACL callouts.
 
+I wanted to switch to gnutls_certificate_set_verify_function() so that
+certificate rejection could happen during handshake where it belongs, rather
+than being dropped afterwards, but that was introduced in 2.10.0 and Debian
+(6.0.5) is still on 2.8.6.  So for now we have to stick with sub-par behaviour.
 
-#define UNKNOWN_NAME "unknown"
-#define DH_BITS      1024
-#define PARAM_SIZE 2*1024
+(I wasn't looking for libraries quite that old, when updating to get rid of
+compiler warnings of deprecated APIs.  If it turns out that a lot of the rest
+require current GnuTLS, then we'll drop support for the ancient libraries).
+*/
 
+#include <gnutls/gnutls.h>
+/* needed for cert checks in verification and DN extraction: */
+#include <gnutls/x509.h>
+/* man-page is incorrect, gnutls_rnd() is not in gnutls.h: */
+#include <gnutls/crypto.h>
 
-/* Values for verify_requirment */
+/* GnuTLS 2 vs 3
 
-enum { VERIFY_NONE, VERIFY_OPTIONAL, VERIFY_REQUIRED };
+GnuTLS 3 only:
+  gnutls_global_set_audit_log_function()
 
-/* Local static variables for GNUTLS */
+Changes:
+  gnutls_certificate_verify_peers2(): is new, drop the 2 for old version
+*/
 
-static host_item *client_host;
+/* Local static variables for GnuTLS */
 
-static gnutls_dh_params dh_params = NULL;
+/* Values for verify_requirement */
 
-static gnutls_certificate_server_credentials x509_cred = NULL;
-static gnutls_session tls_session = NULL;
+enum peer_verify_requirement { VERIFY_NONE, VERIFY_OPTIONAL, VERIFY_REQUIRED };
 
-static char ssl_errstring[256];
+/* This holds most state for server or client; with this, we can set up an
+outbound TLS-enabled connection in an ACL callout, while not stomping all
+over the TLS variables available for expansion.
 
-static int  ssl_session_timeout = 200;
-static int  verify_requirement;
+Some of these correspond to variables in globals.c; those variables will
+be set to point to content in one of these instances, as appropriate for
+the stage of the process lifetime.
 
-/* Priorities for TLS algorithms to use. In each case there's a default table,
-and space into which it can be copied and altered. */
+Not handled here: globals tls_active, tls_bits, tls_cipher, tls_peerdn,
+tls_certificate_verified, tls_channelbinding_b64, tls_sni.
+*/
 
-static const int default_proto_priority[16] = {
-  /* These are gnutls_protocol_t enum values */
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
-  GNUTLS_TLS1_2,
-#endif
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
-  GNUTLS_TLS1_1,
-#endif
-  GNUTLS_TLS1,
-  GNUTLS_SSL3,
-  0 };
+typedef struct exim_gnutls_state {
+  gnutls_session_t session;
+  gnutls_certificate_credentials_t x509_cred;
+  gnutls_priority_t priority_cache;
+  enum peer_verify_requirement verify_requirement;
+  int fd_in;
+  int fd_out;
+  BOOL peer_cert_verified;
+  BOOL trigger_sni_changes;
+  const struct host_item *host;
+  uschar *peerdn;
+  uschar *received_sni;
+
+  const uschar *tls_certificate;
+  const uschar *tls_privatekey;
+  const uschar *tls_sni; /* client send only, not received */
+  const uschar *tls_verify_certificates;
+  const uschar *tls_crl;
+  const uschar *tls_require_ciphers;
+  uschar *exp_tls_certificate;
+  uschar *exp_tls_privatekey;
+  uschar *exp_tls_sni;
+  uschar *exp_tls_verify_certificates;
+  uschar *exp_tls_crl;
+  uschar *exp_tls_require_ciphers;
+
+  uschar *xfer_buffer;
+  int xfer_buffer_lwm;
+  int xfer_buffer_hwm;
+  int xfer_eof;
+  int xfer_error;
+
+  uschar cipherbuf[256];
+} exim_gnutls_state_st;
+
+static const exim_gnutls_state_st exim_gnutls_state_init = {
+  NULL, NULL, NULL, VERIFY_NONE, -1, -1, FALSE, FALSE,
+  NULL, NULL, NULL,
+  NULL, NULL, NULL, NULL, NULL, NULL,
+  NULL, NULL, NULL, NULL, NULL, NULL,
+  NULL, 0, 0, 0, 0,
+  ""
+};
 
-static int proto_priority[16];
+/* Not only do we have our own APIs which don't pass around state, assuming
+it's held in globals, GnuTLS doesn't appear to let us register callback data
+for callbacks, or as part of the session, so we have to keep a "this is the
+context we're currently dealing with" pointer and rely upon being
+single-threaded to keep from processing data on an inbound TLS connection while
+talking to another TLS connection for an outbound check.  This does mean that
+there's no way for heart-beats to be responded to, for the duration of the
+second connection. */
 
-static const int default_kx_priority[16] = {
-  GNUTLS_KX_RSA,
-  GNUTLS_KX_DHE_DSS,
-  GNUTLS_KX_DHE_RSA,
-  0 };
+static exim_gnutls_state_st state_server, state_client;
+static exim_gnutls_state_st *current_global_tls_state;
 
-static int kx_priority[16];
+/* dh_params are initialised once within the lifetime of a process using TLS;
+if we used TLS in a long-lived daemon, we'd have to reconsider this.  But we
+don't want to repeat this. */
 
-static int default_cipher_priority[16] = {
-  GNUTLS_CIPHER_AES_256_CBC,
-  GNUTLS_CIPHER_AES_128_CBC,
-  GNUTLS_CIPHER_3DES_CBC,
-  GNUTLS_CIPHER_ARCFOUR_128,
-  0 };
+static gnutls_dh_params_t dh_server_params = NULL;
 
-static int cipher_priority[16];
+/* No idea how this value was chosen; preserving it.  Default is 3600. */
 
-static const int default_mac_priority[16] = {
-  GNUTLS_MAC_SHA,
-  GNUTLS_MAC_MD5,
-  0 };
+static const int ssl_session_timeout = 200;
 
-static int mac_priority[16];
+static const char * const exim_default_gnutls_priority = "NORMAL";
 
-/* These two are currently not changeable. */
+/* Guard library core initialisation */
 
-static const int comp_priority[16] = { GNUTLS_COMP_NULL, 0 };
-static const int cert_type_priority[16] = { GNUTLS_CRT_X509, 0 };
+static BOOL exim_gnutls_base_init_done = FALSE;
 
-/* Tables of priority names and equivalent numbers */
 
-typedef struct pri_item {
-  uschar *name;
-  int *values;
-} pri_item;
+/* ------------------------------------------------------------------------ */
+/* Callback declarations */
 
+static void exim_gnutls_logger_cb(int level, const char *message);
+static int exim_sni_handling_cb(gnutls_session_t session);
 
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
-static int tls1_2_codes[] = { GNUTLS_TLS1_2, 0 };
-#endif
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
-static int tls1_1_codes[] = { GNUTLS_TLS1_1, 0 };
-#endif
-/* more recent libraries define this as an equivalent value to the
-canonical GNUTLS_TLS1_0; since they're the same, we stick to the
-older name. */
-static int tls1_0_codes[] = { GNUTLS_TLS1, 0 };
-static int ssl3_codes[] = { GNUTLS_SSL3, 0 };
-
-static pri_item proto_index[] = {
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
-  { US"TLS1.2", tls1_2_codes },
-#endif
-#if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
-  { US"TLS1.1", tls1_1_codes },
-#endif
-  { US"TLS1.0", tls1_0_codes },
-  { US"TLS1", tls1_0_codes },
-  { US"SSL3", ssl3_codes }
-};
+/* ------------------------------------------------------------------------ */
+/* macros */
 
+#define MAX_HOST_LEN 255
 
-static int kx_rsa_codes[]      = { GNUTLS_KX_RSA,
-                                   GNUTLS_KX_DHE_RSA, 0 };
-static int kx_dhe_codes[]      = { GNUTLS_KX_DHE_DSS,
-                                   GNUTLS_KX_DHE_RSA, 0 };
-static int kx_dhe_dss_codes[]  = { GNUTLS_KX_DHE_DSS, 0 };
-static int kx_dhe_rsa_codes[]  = { GNUTLS_KX_DHE_RSA, 0 };
-
-static pri_item kx_index[] = {
-  { US"DHE_DSS", kx_dhe_dss_codes },
-  { US"DHE_RSA", kx_dhe_rsa_codes },
-  { US"RSA", kx_rsa_codes },
-  { US"DHE", kx_dhe_codes }
-};
+/* Set this to control gnutls_global_set_log_level(); values 0 to 9 will setup
+the library logging; a value less than 0 disables the calls to set up logging
+callbacks. */
+#define EXIM_GNUTLS_LIBRARY_LOG_LEVEL -1
 
+#define EXIM_CLIENT_DH_MIN_BITS 1024
 
-static int arcfour_128_codes[] = { GNUTLS_CIPHER_ARCFOUR_128, 0 };
-static int arcfour_40_codes[]  = { GNUTLS_CIPHER_ARCFOUR_40, 0 };
-static int arcfour_codes[]     = { GNUTLS_CIPHER_ARCFOUR_128,
-                                   GNUTLS_CIPHER_ARCFOUR_40, 0 };
-static int aes_256_codes[]     = { GNUTLS_CIPHER_AES_256_CBC, 0 };
-static int aes_128_codes[]     = { GNUTLS_CIPHER_AES_128_CBC, 0 };
-static int aes_codes[]         = { GNUTLS_CIPHER_AES_256_CBC,
-                                   GNUTLS_CIPHER_AES_128_CBC, 0 };
-static int des3_codes[]        = { GNUTLS_CIPHER_3DES_CBC, 0 };
-
-static pri_item cipher_index[] = {
-  { US"ARCFOUR_128", arcfour_128_codes },
-  { US"ARCFOUR_40", arcfour_40_codes },
-  { US"ARCFOUR", arcfour_codes },
-  { US"AES_256", aes_256_codes },
-  { US"AES_128", aes_128_codes },
-  { US"AES", aes_codes },
-  { US"3DES", des3_codes }
-};
+#define exim_gnutls_err_check(Label) do { \
+  if (rc != GNUTLS_E_SUCCESS) { return tls_error((Label), gnutls_strerror(rc), host); } } while (0)
 
+#define exim_gnutls_err_debugreturn0(Label) do { \
+  if (rc != GNUTLS_E_SUCCESS) { \
+    DEBUG(D_tls) debug_printf("TLS failure: %s: %s", (Label), gnutls_strerror(rc)); \
+    return 0; } } while (0)
 
-static int mac_sha_codes[]     = { GNUTLS_MAC_SHA, 0 };
-static int mac_md5_codes[]     = { GNUTLS_MAC_MD5, 0 };
-
-static pri_item mac_index[] = {
-  { US"SHA",  mac_sha_codes },
-  { US"SHA1", mac_sha_codes },
-  { US"MD5",  mac_md5_codes }
-};
+#define expand_check_tlsvar(Varname) expand_check(state->Varname, US #Varname, &state->exp_##Varname)
 
+#if GNUTLS_VERSION_NUMBER >= 0x020c00
+#define HAVE_GNUTLS_SESSION_CHANNEL_BINDING
+#endif
 
+/* ------------------------------------------------------------------------ */
+/* Static functions */
 
 /*************************************************
 *               Handle TLS error                 *
@@ -188,120 +188,169 @@ some shared functions.
 
 Argument:
   prefix    text to include in the logged error
-  host      NULL if setting up a server;
-            the connected host if setting up a client
   msg       additional error string (may be NULL)
             usually obtained from gnutls_strerror()
+  host      NULL if setting up a server;
+            the connected host if setting up a client
 
 Returns:    OK/DEFER/FAIL
 */
 
 static int
-tls_error(uschar *prefix, host_item *host, const char *msg)
+tls_error(const uschar *prefix, const char *msg, const host_item *host)
 {
-if (host == NULL)
+if (host)
+  {
+  log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s)%s%s",
+      host->name, host->address, prefix, msg ? ": " : "", msg ? msg : "");
+  return FAIL;
+  }
+else
   {
   uschar *conn_info = smtp_get_connection_info();
-  if (strncmp(conn_info, "SMTP ", 5) == 0)
+  if (Ustrncmp(conn_info, US"SMTP ", 5) == 0)
     conn_info += 5;
   log_write(0, LOG_MAIN, "TLS error on %s (%s)%s%s",
-    conn_info, prefix, msg ? ": " : "", msg ? msg : "");
+      conn_info, prefix, msg ? ": " : "", msg ? msg : "");
   return DEFER;
   }
-else
-  {
-  log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s)%s%s",
-    host->name, host->address, prefix, msg ? ": " : "", msg ? msg : "");
-  return FAIL;
-  }
 }
 
 
 
+
 /*************************************************
-*             Verify certificate                 *
+*    Deal with logging errors during I/O         *
 *************************************************/
 
-/* Called after a successful handshake, when certificate verification is
-required or optional, for both server and client.
+/* We have to get the identity of the peer from saved data.
 
-Arguments:
-  session    GNUTLS session
-  error      where to put text giving a reason for failure
+Argument:
+  state    the current GnuTLS exim state container
+  rc       the GnuTLS error code, or 0 if it's a local error
+  when     text identifying read or write
+  text     local error text when ec is 0
 
-Returns:     TRUE/FALSE
+Returns:   nothing
 */
 
-static BOOL
-verify_certificate(gnutls_session session, const char **error)
+static void
+record_io_error(exim_gnutls_state_st *state, int rc, uschar *when, uschar *text)
 {
-int rc = -1;
-uschar *dn_string = US"";
-const gnutls_datum *cert;
-unsigned int verify, cert_size = 0;
+const char *msg;
 
-*error = NULL;
+if (rc == GNUTLS_E_FATAL_ALERT_RECEIVED)
+  msg = CS string_sprintf("%s: %s", US gnutls_strerror(rc),
+    US gnutls_alert_get_name(gnutls_alert_get(state->session)));
+else
+  msg = gnutls_strerror(rc);
 
-/* Get the peer's certificate. If it sent one, extract it's DN, and then
-attempt to verify the certificate. If no certificate is supplied, verification
-is forced to fail. */
+tls_error(when, msg, state->host);
+}
 
-cert = gnutls_certificate_get_peers(session, &cert_size);
-if (cert != NULL)
-  {
-  uschar buff[1024];
-  gnutls_x509_crt gcert;
 
-  gnutls_x509_crt_init(&gcert);
-  dn_string = US"unknown";
 
-  if (gnutls_x509_crt_import(gcert, cert, GNUTLS_X509_FMT_DER) == 0)
-    {
-    size_t bufsize = sizeof(buff);
-    if (gnutls_x509_crt_get_dn(gcert, CS buff, &bufsize) >= 0)
-      dn_string = string_copy_malloc(buff);
-    }
 
-  rc = gnutls_certificate_verify_peers2(session, &verify);
-  }
-else
-  {
-  DEBUG(D_tls) debug_printf("no peer certificate supplied\n");
-  verify = GNUTLS_CERT_INVALID;
-  *error = "not supplied";
-  }
+/*************************************************
+*        Set various Exim expansion vars         *
+*************************************************/
 
-/* Handle the result of verification. INVALID seems to be set as well
-as REVOKED, but leave the test for both. */
+/* We set various Exim global variables from the state, once a session has
+been established.  With TLS callouts, may need to change this to stack
+variables, or just re-call it with the server state after client callout
+has finished.
 
-if ((rc < 0) || (verify & (GNUTLS_CERT_INVALID|GNUTLS_CERT_REVOKED)) != 0)
-  {
-  tls_certificate_verified = FALSE;
-  if (*error == NULL) *error = ((verify & GNUTLS_CERT_REVOKED) != 0)?
-    "revoked" : "invalid";
-  if (verify_requirement == VERIFY_REQUIRED)
-    {
-    DEBUG(D_tls) debug_printf("TLS certificate verification failed (%s): "
-      "peerdn=%s\n", *error, dn_string);
-    gnutls_alert_send(session, GNUTLS_AL_FATAL, GNUTLS_A_BAD_CERTIFICATE);
-    return FALSE;                       /* reject */
-    }
-  DEBUG(D_tls) debug_printf("TLS certificate verify failure (%s) overridden "
-      "(host in tls_try_verify_hosts): peerdn=%s\n", *error, dn_string);
-  }
-else
+Make sure anything set here is inset in tls_getc().
+
+Sets:
+  tls_active                fd
+  tls_bits                  strength indicator
+  tls_certificate_verified  bool indicator
+  tls_channelbinding_b64    for some SASL mechanisms
+  tls_cipher                a string
+  tls_peerdn                a string
+  tls_sni                   a (UTF-8) string
+Also:
+  current_global_tls_state  for API limitations
+
+Argument:
+  state      the relevant exim_gnutls_state_st *
+*/
+
+static void
+extract_exim_vars_from_tls_state(exim_gnutls_state_st *state)
+{
+gnutls_protocol_t protocol;
+gnutls_cipher_algorithm_t cipher;
+gnutls_kx_algorithm_t kx;
+gnutls_mac_algorithm_t mac;
+uschar *p;
+#ifdef HAVE_GNUTLS_SESSION_CHANNEL_BINDING
+int old_pool;
+int rc;
+gnutls_datum_t channel;
+#endif
+
+current_global_tls_state = state;
+
+tls_active = state->fd_out;
+
+cipher = gnutls_cipher_get(state->session);
+/* returns size in "bytes" */
+tls_bits = gnutls_cipher_get_key_size(cipher) * 8;
+
+if (!*state->cipherbuf)
   {
-  tls_certificate_verified = TRUE;
-  DEBUG(D_tls) debug_printf("TLS certificate verified: peerdn=%s\n",
-    dn_string);
+  protocol = gnutls_protocol_get_version(state->session);
+  mac = gnutls_mac_get(state->session);
+  kx = gnutls_kx_get(state->session);
+
+  string_format(state->cipherbuf, sizeof(state->cipherbuf),
+      "%s:%s:%u",
+      gnutls_protocol_get_name(protocol),
+      gnutls_cipher_suite_get_name(kx, cipher, mac),
+      tls_bits);
+
+  /* I don't see a way that spaces could occur, in the current GnuTLS
+  code base, but it was a concern in the old code and perhaps older GnuTLS
+  releases did return "TLS 1.0"; play it safe, just in case. */
+  for (p = state->cipherbuf; *p != '\0'; ++p)
+    if (isspace(*p))
+      *p = '-';
   }
+tls_cipher = state->cipherbuf;
+
+DEBUG(D_tls) debug_printf("cipher: %s\n", tls_cipher);
+
+tls_certificate_verified = state->peer_cert_verified;
 
-tls_peerdn = dn_string;
-return TRUE;                            /* accept */
+/* note that tls_channelbinding_b64 is not saved to the spool file, since it's
+only available for use for authenticators while this TLS session is running. */
+
+tls_channelbinding_b64 = NULL;
+#ifdef HAVE_GNUTLS_SESSION_CHANNEL_BINDING
+channel.data = NULL;
+channel.size = 0;
+rc = gnutls_session_channel_binding(state->session, GNUTLS_CB_TLS_UNIQUE, &channel);
+if (rc) {
+  DEBUG(D_tls) debug_printf("Channel binding error: %s\n", gnutls_strerror(rc));
+} else {
+  old_pool = store_pool;
+  store_pool = POOL_PERM;
+  tls_channelbinding_b64 = auth_b64encode(channel.data, (int)channel.size);
+  store_pool = old_pool;
+  DEBUG(D_tls) debug_printf("Have channel bindings cached for possible auth usage.\n");
+}
+#endif
+
+tls_peerdn = state->peerdn;
+
+tls_sni = state->received_sni;
 }
 
 
 
+
 /*************************************************
 *            Setup up DH parameters              *
 *************************************************/
@@ -323,23 +372,30 @@ Returns:     OK/DEFER/FAIL
 */
 
 static int
-init_dh(host_item *host)
+init_server_dh(void)
 {
-int fd;
-int ret;
+int fd, rc;
+unsigned int dh_bits;
 gnutls_datum m;
-uschar filename[200];
+uschar filename[PATH_MAX];
+size_t sz;
+host_item *host = NULL; /* dummy for macros */
+const char * const dh_param_fn_ext = "normal"; /* change as dh_bits changes */
 
-/* Initialize the data structures for holding the parameters */
+DEBUG(D_tls) debug_printf("Initialising GnuTLS server params.\n");
 
-ret = gnutls_dh_params_init(&dh_params);
-if (ret < 0) return tls_error(US"init dh_params", host, gnutls_strerror(ret));
+rc = gnutls_dh_params_init(&dh_server_params);
+exim_gnutls_err_check(US"gnutls_dh_params_init");
 
-/* Set up the name of the cache file */
+/* If you change this, also change dh_param_fn_ext so that we can use a
+different filename and ensure we have sufficient bits. */
+dh_bits = gnutls_sec_param_to_pk_bits(GNUTLS_PK_DH, GNUTLS_SEC_PARAM_NORMAL);
+if (!dh_bits)
+  return tls_error(US"gnutls_sec_param_to_pk_bits() failed", NULL, NULL);
 
-if (!string_format(filename, sizeof(filename), "%s/gnutls-params",
-      spool_directory))
-  return tls_error(US"overlong filename", host, NULL);
+if (!string_format(filename, sizeof(filename),
+      "%s/gnutls-params-%s", spool_directory, dh_param_fn_ext))
+  return tls_error(US"overlong filename", NULL, NULL);
 
 /* Open the cache file for reading and if successful, read it and set up the
 parameters. */
@@ -348,27 +404,50 @@ fd = Uopen(filename, O_RDONLY, 0);
 if (fd >= 0)
   {
   struct stat statbuf;
-  if (fstat(fd, &statbuf) < 0)
+  FILE *fp;
+  int saved_errno;
+
+  if (fstat(fd, &statbuf) < 0)  /* EIO */
+    {
+    saved_errno = errno;
+    (void)close(fd);
+    return tls_error(US"TLS cache stat failed", strerror(saved_errno), NULL);
+    }
+  if (!S_ISREG(statbuf.st_mode))
     {
     (void)close(fd);
-    return tls_error(US"TLS cache stat failed", host, strerror(errno));
+    return tls_error(US"TLS cache not a file", NULL, NULL);
+    }
+  fp = fdopen(fd, "rb");
+  if (!fp)
+    {
+    saved_errno = errno;
+    (void)close(fd);
+    return tls_error(US"fdopen(TLS cache stat fd) failed",
+        strerror(saved_errno), NULL);
     }
 
   m.size = statbuf.st_size;
   m.data = malloc(m.size);
   if (m.data == NULL)
-    return tls_error(US"memory allocation failed", host, strerror(errno));
-  errno = 0;
-  if (read(fd, m.data, m.size) != m.size)
-    return tls_error(US"TLS cache read failed", host, strerror(errno));
-  (void)close(fd);
-
-  ret = gnutls_dh_params_import_pkcs3(dh_params, &m, GNUTLS_X509_FMT_PEM);
-  if (ret < 0)
-    return tls_error(US"DH params import", host, gnutls_strerror(ret));
-  DEBUG(D_tls) debug_printf("read D-H parameters from file\n");
+    {
+    fclose(fp);
+    return tls_error(US"malloc failed", strerror(errno), NULL);
+    }
+  sz = fread(m.data, m.size, 1, fp);
+  if (!sz)
+    {
+    saved_errno = errno;
+    fclose(fp);
+    free(m.data);
+    return tls_error(US"fread failed", strerror(saved_errno), NULL);
+    }
+  fclose(fp);
 
+  rc = gnutls_dh_params_import_pkcs3(dh_server_params, &m, GNUTLS_X509_FMT_PEM);
   free(m.data);
+  exim_gnutls_err_check(US"gnutls_dh_params_import_pkcs3");
+  DEBUG(D_tls) debug_printf("read D-H parameters from file \"%s\"\n", filename);
   }
 
 /* If the file does not exist, fall through to compute new data and cache it.
@@ -376,13 +455,13 @@ If there was any other opening error, it is serious. */
 
 else if (errno == ENOENT)
   {
-  ret = -1;
+  rc = -1;
   DEBUG(D_tls)
-    debug_printf("parameter cache file %s does not exist\n", filename);
+    debug_printf("D-H parameter cache file \"%s\" does not exist\n", filename);
   }
 else
-  return tls_error(string_open_failed(errno, "%s for reading", filename),
-    host, NULL);
+  return tls_error(string_open_failed(errno, "\"%s\" for reading", filename),
+      NULL, NULL);
 
 /* If ret < 0, either the cache file does not exist, or the data it contains
 is not useful. One particular case of this is when upgrading from an older
@@ -390,59 +469,72 @@ release of Exim in which the data was stored in a different format. We don't
 try to be clever and support both formats; we just regenerate new data in this
 case. */
 
-if (ret < 0)
+if (rc < 0)
   {
-  uschar tempfilename[sizeof(filename) + 10];
+  uschar *temp_fn;
 
-  DEBUG(D_tls) debug_printf("generating %d bit Diffie-Hellman key...\n",
-    DH_BITS);
-  ret = gnutls_dh_params_generate2(dh_params, DH_BITS);
-  if (ret < 0) return tls_error(US"D-H key generation", host, gnutls_strerror(ret));
+  if ((PATH_MAX - Ustrlen(filename)) < 10)
+    return tls_error(US"Filename too long to generate replacement",
+        CS filename, NULL);
 
-  /* Write the parameters to a file in the spool directory so that we
-  can use them from other Exim processes. */
-
-  sprintf(CS tempfilename, "%s-%d", filename, (int)getpid());
-  fd = Uopen(tempfilename, O_WRONLY|O_CREAT, 0400);
+  temp_fn = string_copy(US "%s.XXXXXXX");
+  fd = mkstemp(CS temp_fn); /* modifies temp_fn */
   if (fd < 0)
-    return tls_error(string_open_failed(errno, "%s for writing", filename),
-      host, NULL);
+    return tls_error(US"Unable to open temp file", strerror(errno), NULL);
   (void)fchown(fd, exim_uid, exim_gid);   /* Probably not necessary */
 
-  /* export the parameters in a format that can be generated using GNUTLS'
-   * certtool or other programs.
-   *
-   * The commands for certtool are:
-   * $ certtool --generate-dh-params --bits 1024 > params
-   */
-
-  m.size = PARAM_SIZE;
+  DEBUG(D_tls) debug_printf("generating %d bits Diffie-Hellman key ...\n", dh_bits);
+  rc = gnutls_dh_params_generate2(dh_server_params, dh_bits);
+  exim_gnutls_err_check(US"gnutls_dh_params_generate2");
+
+  /* gnutls_dh_params_export_pkcs3() will tell us the exact size, every time,
+  and I confirmed that a NULL call to get the size first is how the GnuTLS
+  sample apps handle this. */
+
+  sz = 0;
+  m.data = NULL;
+  rc = gnutls_dh_params_export_pkcs3(dh_server_params, GNUTLS_X509_FMT_PEM,
+      m.data, &sz);
+  if (rc != GNUTLS_E_SHORT_MEMORY_BUFFER)
+    exim_gnutls_err_check(US"gnutls_dh_params_export_pkcs3(NULL) sizing");
+  m.size = sz;
   m.data = malloc(m.size);
   if (m.data == NULL)
-    return tls_error(US"memory allocation failed", host, strerror(errno));
-
-  m.size = PARAM_SIZE;
-  ret = gnutls_dh_params_export_pkcs3(dh_params, GNUTLS_X509_FMT_PEM, m.data,
-    &m.size);
-  if (ret < 0)
-    return tls_error(US"DH params export", host, gnutls_strerror(ret));
-
-  m.size = Ustrlen(m.data);
-  errno = 0;
-  if (write(fd, m.data, m.size) != m.size || write(fd, "\n", 1) != 1)
-    return tls_error(US"TLS cache write failed", host, strerror(errno));
+    return tls_error(US"memory allocation failed", strerror(errno), NULL);
+  rc = gnutls_dh_params_export_pkcs3(dh_server_params, GNUTLS_X509_FMT_PEM,
+      m.data, &sz);
+  if (rc != GNUTLS_E_SUCCESS)
+    {
+    free(m.data);
+    exim_gnutls_err_check(US"gnutls_dh_params_export_pkcs3() real");
+    }
 
+  sz = write_to_fd_buf(fd, m.data, (size_t) m.size);
+  if (sz != m.size)
+    {
+    free(m.data);
+    return tls_error(US"TLS cache write D-H params failed",
+        strerror(errno), NULL);
+    }
   free(m.data);
-  (void)close(fd);
+  sz = write_to_fd_buf(fd, US"\n", 1);
+  if (sz != 1)
+    return tls_error(US"TLS cache write D-H params final newline failed",
+        strerror(errno), NULL);
+
+  rc = close(fd);
+  if (rc)
+    return tls_error(US"TLS cache write close() failed",
+        strerror(errno), NULL);
 
-  if (rename(CS tempfilename, CS filename) < 0)
-    return tls_error(string_sprintf("failed to rename %s as %s",
-      tempfilename, filename), host, strerror(errno));
+  if (Urename(temp_fn, filename) < 0)
+    return tls_error(string_sprintf("failed to rename \"%s\" as \"%s\"",
+          temp_fn, filename), strerror(errno), NULL);
 
-  DEBUG(D_tls) debug_printf("wrote D-H parameters to file %s\n", filename);
+  DEBUG(D_tls) debug_printf("wrote D-H parameters to file \"%s\"\n", filename);
   }
 
-DEBUG(D_tls) debug_printf("initialized D-H parameters\n");
+DEBUG(D_tls) debug_printf("initialized server D-H parameters\n");
 return OK;
 }
 
@@ -450,90 +542,116 @@ return OK;
 
 
 /*************************************************
-*            Initialize for GnuTLS               *
+*       Variables re-expanded post-SNI           *
 *************************************************/
 
-/* Called from both server and client code. In the case of a server, errors
-before actual TLS negotiation return DEFER.
+/* Called from both server and client code, via tls_init(), and also from
+the SNI callback after receiving an SNI, if tls_certificate includes "tls_sni".
+
+We can tell the two apart by state->received_sni being non-NULL in callback.
+
+The callback should not call us unless state->trigger_sni_changes is true,
+which we are responsible for setting on the first pass through.
 
 Arguments:
-  host            connected host, if client; NULL if server
-  certificate     certificate file
-  privatekey      private key file
-  cas             CA certs file
-  crl             CRL file
+  state           exim_gnutls_state_st *
 
 Returns:          OK/DEFER/FAIL
 */
 
 static int
-tls_init(host_item *host, uschar *certificate, uschar *privatekey, uschar *cas,
-  uschar *crl)
+tls_expand_session_files(exim_gnutls_state_st *state)
 {
 int rc;
-uschar *cert_expanded, *key_expanded, *cas_expanded, *crl_expanded;
-
-client_host = host;
+const host_item *host = state->host;  /* macro should be reconsidered? */
+uschar *saved_tls_certificate = NULL;
+uschar *saved_tls_privatekey = NULL;
+uschar *saved_tls_verify_certificates = NULL;
+uschar *saved_tls_crl = NULL;
+int cert_count;
+
+/* We check for tls_sni *before* expansion. */
+if (!state->host)
+  {
+  if (!state->received_sni)
+    {
+    if (Ustrstr(state->tls_certificate, US"tls_sni"))
+      {
+      DEBUG(D_tls) debug_printf("We will re-expand TLS session files if we receive SNI.\n");
+      state->trigger_sni_changes = TRUE;
+      }
+    }
+  else
+    {
+    saved_tls_certificate = state->exp_tls_certificate;
+    saved_tls_privatekey = state->exp_tls_privatekey;
+    saved_tls_verify_certificates = state->exp_tls_verify_certificates;
+    saved_tls_crl = state->exp_tls_crl;
+    }
+  }
 
-rc = gnutls_global_init();
-if (rc < 0) return tls_error(US"tls-init", host, gnutls_strerror(rc));
+/* remember: expand_check_tlsvar() is expand_check() but fiddling with
+state members, assuming consistent naming; and expand_check() returns
+false if expansion failed, unless expansion was forced to fail. */
 
-/* Create D-H parameters, or read them from the cache file. This function does
-its own SMTP error messaging. */
+/* check if we at least have a certificate, before doing expensive
+D-H generation. */
 
-rc = init_dh(host);
-if (rc != OK) return rc;
+if (!expand_check_tlsvar(tls_certificate))
+  return DEFER;
 
-/* Create the credentials structure */
+/* certificate is mandatory in server, optional in client */
 
-rc = gnutls_certificate_allocate_credentials(&x509_cred);
-if (rc < 0)
-  return tls_error(US"certificate_allocate_credentials",
-    host, gnutls_strerror(rc));
-
-/* This stuff must be done for each session, because different certificates
-may be required for different sessions. */
+if ((state->exp_tls_certificate == NULL) ||
+    (*state->exp_tls_certificate == '\0'))
+  {
+  if (state->host == NULL)
+    return tls_error(US"no TLS server certificate is specified", NULL, NULL);
+  else
+    DEBUG(D_tls) debug_printf("TLS: no client certificate specified; okay\n");
+  }
 
-if (!expand_check(certificate, US"tls_certificate", &cert_expanded))
+if (state->tls_privatekey && !expand_check_tlsvar(tls_privatekey))
   return DEFER;
 
-key_expanded = NULL;
-if (privatekey != NULL)
+/* tls_privatekey is optional, defaulting to same file as certificate */
+
+if (state->tls_privatekey == NULL || *state->tls_privatekey == '\0')
   {
-  if (!expand_check(privatekey, US"tls_privatekey", &key_expanded))
-    return DEFER;
+  state->tls_privatekey = state->tls_certificate;
+  state->exp_tls_privatekey = state->exp_tls_certificate;
   }
 
-/* If expansion was forced to fail, key_expanded will be NULL. If the result of
-the expansion is an empty string, ignore it also, and assume that the private
-key is in the same file as the certificate. */
-
-if (key_expanded == NULL || *key_expanded == 0)
-  key_expanded = cert_expanded;
 
-/* Set the certificate and private keys */
-
-if (cert_expanded != NULL)
+if (state->exp_tls_certificate && *state->exp_tls_certificate)
   {
+  BOOL setit = TRUE;
   DEBUG(D_tls) debug_printf("certificate file = %s\nkey file = %s\n",
-    cert_expanded, key_expanded);
-  rc = gnutls_certificate_set_x509_key_file(x509_cred, CS cert_expanded,
-    CS key_expanded, GNUTLS_X509_FMT_PEM);
-  if (rc < 0)
+      state->exp_tls_certificate, state->exp_tls_privatekey);
+
+  if (state->received_sni)
     {
-    uschar *msg = string_sprintf("cert/key setup: cert=%s key=%s",
-      cert_expanded, key_expanded);
-    return tls_error(msg, host, gnutls_strerror(rc));
+    if ((Ustrcmp(state->exp_tls_certificate, saved_tls_certificate) == 0) &&
+        (Ustrcmp(state->exp_tls_privatekey, saved_tls_privatekey) == 0))
+      {
+      DEBUG(D_tls) debug_printf("cert and key unchanged with SNI.\n");
+      setit = FALSE;
+      }
+    else
+      {
+      DEBUG(D_tls) debug_printf("SNI changed cert/key pair.\n");
+      }
     }
-  }
 
-/* A certificate is mandatory in a server, but not in a client */
-
-else
-  {
-  if (host == NULL)
-    return tls_error(US"no TLS server certificate is specified", NULL, NULL);
-  DEBUG(D_tls) debug_printf("no TLS client certificate is specified\n");
+  if (setit)
+    {
+    rc = gnutls_certificate_set_x509_key_file(state->x509_cred,
+        CS state->exp_tls_certificate, CS state->exp_tls_privatekey,
+        GNUTLS_X509_FMT_PEM);
+    exim_gnutls_err_check(
+        string_sprintf("cert/key setup: cert=%s key=%s",
+          state->exp_tls_certificate, state->exp_tls_privatekey));
+    }
   }
 
 /* Set the trusted CAs file if one is provided, and then add the CRL if one is
@@ -542,359 +660,516 @@ error message is provided. However, if we just refrain from setting anything up
 in that case, certificate verification fails, which seems to be the correct
 behaviour. */
 
-if (cas != NULL)
+if (state->tls_verify_certificates && *state->tls_verify_certificates)
   {
   struct stat statbuf;
+  BOOL setit_vc = TRUE, setit_crl = TRUE;
 
-  if (!expand_check(cas, US"tls_verify_certificates", &cas_expanded))
+  if (!expand_check_tlsvar(tls_verify_certificates))
     return DEFER;
+  if (state->tls_crl && *state->tls_crl)
+    if (!expand_check_tlsvar(tls_crl))
+      return DEFER;
 
-  if (stat(CS cas_expanded, &statbuf) < 0)
+  if (state->received_sni)
+    {
+    if (Ustrcmp(state->exp_tls_verify_certificates, saved_tls_verify_certificates) == 0)
+      setit_vc = FALSE;
+    if (Ustrcmp(state->exp_tls_crl, saved_tls_crl) == 0)
+      setit_crl = FALSE;
+    }
+
+  /* nb: early exit; change if add more expansions to this function */
+  if (!(setit_vc || setit_crl))
+    return OK;
+
+  if (Ustat(state->exp_tls_verify_certificates, &statbuf) < 0)
     {
     log_write(0, LOG_MAIN|LOG_PANIC, "could not stat %s "
-      "(tls_verify_certificates): %s", cas_expanded, strerror(errno));
+        "(tls_verify_certificates): %s", state->exp_tls_verify_certificates,
+        strerror(errno));
+    return DEFER;
+    }
+
+  if (!S_ISREG(statbuf.st_mode))
+    {
+    DEBUG(D_tls)
+      debug_printf("verify certificates path is not a file: \"%s\"\n%s\n",
+          state->exp_tls_verify_certificates,
+          S_ISDIR(statbuf.st_mode)
+            ? " it's a directory, that's OpenSSL, this is GnuTLS"
+            : " (not a directory either)");
+    log_write(0, LOG_MAIN|LOG_PANIC,
+        "tls_verify_certificates \"%s\" is not a file",
+        state->exp_tls_verify_certificates);
     return DEFER;
     }
 
   DEBUG(D_tls) debug_printf("verify certificates = %s size=" OFF_T_FMT "\n",
-    cas_expanded, statbuf.st_size);
+          state->exp_tls_verify_certificates, statbuf.st_size);
 
-  /* If the cert file is empty, there's no point in loading the CRL file. */
+  /* If the CA cert file is empty, there's no point in loading the CRL file,
+  as we aren't verifying, so checking for revocation is pointless. */
 
   if (statbuf.st_size > 0)
     {
-    rc = gnutls_certificate_set_x509_trust_file(x509_cred, CS cas_expanded,
-      GNUTLS_X509_FMT_PEM);
-    if (rc < 0) return tls_error(US"setup_certs", host, gnutls_strerror(rc));
-
-    if (crl != NULL && *crl != 0)
+    if (setit_vc)
       {
-      if (!expand_check(crl, US"tls_crl", &crl_expanded))
-        return DEFER;
-      DEBUG(D_tls) debug_printf("loading CRL file = %s\n", crl_expanded);
-      rc = gnutls_certificate_set_x509_crl_file(x509_cred, CS crl_expanded,
-        GNUTLS_X509_FMT_PEM);
-      if (rc < 0) return tls_error(US"CRL setup", host, gnutls_strerror(rc));
+      cert_count = gnutls_certificate_set_x509_trust_file(state->x509_cred,
+          CS state->exp_tls_verify_certificates, GNUTLS_X509_FMT_PEM);
+      if (cert_count < 0)
+        {
+        rc = cert_count;
+        exim_gnutls_err_check(US"gnutls_certificate_set_x509_trust_file");
+        }
+      DEBUG(D_tls) debug_printf("Added %d certificate authorities.\n", cert_count);
       }
-    }
-  }
 
-/* Associate the parameters with the x509 credentials structure. */
-
-gnutls_certificate_set_dh_params(x509_cred, dh_params);
+    if (setit_crl && state->tls_crl && *state->tls_crl)
+      {
+      if (state->exp_tls_crl && *state->exp_tls_crl)
+        {
+        DEBUG(D_tls) debug_printf("loading CRL file = %s\n", state->exp_tls_crl);
+        rc = gnutls_certificate_set_x509_crl_file(state->x509_cred,
+            CS state->exp_tls_crl, GNUTLS_X509_FMT_PEM);
+        exim_gnutls_err_check(US"gnutls_certificate_set_x509_crl_file");
+        }
+      }
+    } /* statbuf.st_size */
+  } /* tls_verify_certificates */
 
-DEBUG(D_tls) debug_printf("initialized certificate stuff\n");
 return OK;
+/* also above, during verify_certificates/crl, during SNI, if unchanged */
 }
 
 
 
 
 /*************************************************
-*           Remove from a priority list          *
+*            Initialize for GnuTLS               *
 *************************************************/
 
-/* Cautiously written so that it will remove duplicates if present.
+/* Called from both server and client code. In the case of a server, errors
+before actual TLS negotiation return DEFER.
 
 Arguments:
-  list         a zero-terminated list
-  remove_list  a zero-terminated list to be removed
+  host            connected host, if client; NULL if server
+  certificate     certificate file
+  privatekey      private key file
+  sni             TLS SNI to send, sometimes when client; else NULL
+  cas             CA certs file
+  crl             CRL file
+  require_ciphers tls_require_ciphers setting
 
-Returns:       nothing
+Returns:          OK/DEFER/FAIL
 */
 
-static void
-remove_priority(int *list, int *remove_list)
+static int
+tls_init(
+    const host_item *host,
+    const uschar *certificate,
+    const uschar *privatekey,
+    const uschar *sni,
+    const uschar *cas,
+    const uschar *crl,
+    const uschar *require_ciphers,
+    exim_gnutls_state_st **caller_state)
 {
-for (; *remove_list != 0; remove_list++)
+exim_gnutls_state_st *state;
+int rc;
+size_t sz;
+const char *errpos;
+uschar *p;
+BOOL want_default_priorities;
+
+if (!exim_gnutls_base_init_done)
   {
-  int *p = list;
-  while (*p != 0)
+  DEBUG(D_tls) debug_printf("GnuTLS global init required.\n");
+
+  rc = gnutls_global_init();
+  exim_gnutls_err_check(US"gnutls_global_init");
+
+#if EXIM_GNUTLS_LIBRARY_LOG_LEVEL >= 0
+  DEBUG(D_tls)
     {
-    if (*p == *remove_list)
-      {
-      int *pp = p;
-      do { pp[0] = pp[1]; pp++; } while (*pp != 0);
-      }
-    else p++;
+    gnutls_global_set_log_function(exim_gnutls_logger_cb);
+    /* arbitrarily chosen level; bump upto 9 for more */
+    gnutls_global_set_log_level(EXIM_GNUTLS_LIBRARY_LOG_LEVEL);
     }
+#endif
+
+  exim_gnutls_base_init_done = TRUE;
   }
-}
 
+if (host)
+  {
+  state = &state_client;
+  memcpy(state, &exim_gnutls_state_init, sizeof(exim_gnutls_state_init));
+  DEBUG(D_tls) debug_printf("initialising GnuTLS client session\n");
+  rc = gnutls_init(&state->session, GNUTLS_CLIENT);
+  }
+else
+  {
+  state = &state_server;
+  memcpy(state, &exim_gnutls_state_init, sizeof(exim_gnutls_state_init));
+  DEBUG(D_tls) debug_printf("initialising GnuTLS server session\n");
+  rc = gnutls_init(&state->session, GNUTLS_SERVER);
+  }
+exim_gnutls_err_check(US"gnutls_init");
 
+state->host = host;
 
-/*************************************************
-*            Add to a priority list              *
-*************************************************/
+state->tls_certificate = certificate;
+state->tls_privatekey = privatekey;
+state->tls_sni = sni;
+state->tls_verify_certificates = cas;
+state->tls_crl = crl;
 
-/* Cautiously written to check the list size
+rc = gnutls_certificate_allocate_credentials(&state->x509_cred);
+exim_gnutls_err_check(US"gnutls_certificate_allocate_credentials");
 
-Arguments:
-  list         a zero-terminated list
-  list_max     maximum offset in the list
-  add_list     a zero-terminated list to be added
+/* This handles the variables that might get re-expanded after TLS SNI;
+that's tls_certificate, tls_privatekey, tls_verify_certificates, tls_crl */
 
-Returns:       TRUE if OK; FALSE if list overflows
-*/
+DEBUG(D_tls)
+  debug_printf("Expanding various TLS configuration options for session credentials.\n");
+rc = tls_expand_session_files(state);
+if (rc != OK) return rc;
 
-static BOOL
-add_priority(int *list, int list_max, int *add_list)
-{
-int next = 0;
-while (list[next] != 0) next++;
-while (*add_list != 0)
+/* Create D-H parameters, or read them from the cache file. This function does
+its own SMTP error messaging. This only happens for the server, TLS D-H ignores
+client-side params. */
+
+if (!host)
   {
-  if (next >= list_max) return FALSE;
-  list[next++] = *add_list++;
+  rc = init_server_dh();
+  if (rc != OK) return rc;
+  gnutls_certificate_set_dh_params(state->x509_cred, dh_server_params);
   }
-list[next] = 0;
-return TRUE;
-}
-
-
-
-/*************************************************
-*          Adjust a priority list                *
-*************************************************/
-
-/* This function is called to adjust the lists of cipher algorithms, MAC
-algorithms, key-exchange methods, and protocols.
 
-Arguments:
-  plist       the appropriate priority list
-  psize       the length of the list
-  s           the configuation string
-  index       the index of recognized strings
-  isize       the length of the index
+/* Link the credentials to the session. */
 
+rc = gnutls_credentials_set(state->session, GNUTLS_CRD_CERTIFICATE, state->x509_cred);
+exim_gnutls_err_check(US"gnutls_credentials_set");
 
-  which       text for an error message
+/* set SNI in client, only */
+if (host)
+  {
+  if (!expand_check_tlsvar(tls_sni))
+    return DEFER;
+  if (state->exp_tls_sni && *state->exp_tls_sni)
+    {
+    DEBUG(D_tls)
+      debug_printf("Setting TLS client SNI to \"%s\"\n", state->exp_tls_sni);
+    sz = Ustrlen(state->exp_tls_sni);
+    rc = gnutls_server_name_set(state->session,
+        GNUTLS_NAME_DNS, state->exp_tls_sni, sz);
+    exim_gnutls_err_check(US"gnutls_server_name_set");
+    }
+  }
+else if (state->tls_sni)
+  DEBUG(D_tls) debug_printf("*** PROBABLY A BUG *** " \
+      "have an SNI set for a client [%s]\n", state->tls_sni);
 
-Returns:      FALSE if the table overflows, else TRUE
-*/
+/* This is the priority string support,
+http://www.gnu.org/software/gnutls/manual/html_node/Priority-Strings.html
+and replaces gnutls_require_kx, gnutls_require_mac & gnutls_require_protocols.
+This was backwards incompatible, but means Exim no longer needs to track
+all algorithms and provide string forms for them. */
 
-static BOOL
-set_priority(int *plist, int psize, uschar *s, pri_item *index, int isize,
-   uschar *which)
-{
-int sep = 0;
-BOOL first = TRUE;
-uschar *t;
+want_default_priorities = TRUE;
 
-while ((t = string_nextinlist(&s, &sep, big_buffer, big_buffer_size)) != NULL)
+if (state->tls_require_ciphers && *state->tls_require_ciphers)
   {
-  int i;
-  BOOL exclude = t[0] == '!';
-  if (first && !exclude) plist[0] = 0;
-  first = FALSE;
-  for (i = 0; i < isize; i++)
+  if (!expand_check_tlsvar(tls_require_ciphers))
+    return DEFER;
+  if (state->exp_tls_require_ciphers && *state->exp_tls_require_ciphers)
     {
-    uschar *ss = strstric(t, index[i].name, FALSE);
-    if (ss != NULL)
-      {
-      uschar *endss = ss + Ustrlen(index[i].name);
-      if ((ss == t || !isalnum(ss[-1])) && !isalnum(*endss))
-        {
-        if (exclude)
-          remove_priority(plist, index[i].values);
-        else
-          {
-          if (!add_priority(plist, psize, index[i].values))
-            {
-            log_write(0, LOG_MAIN|LOG_PANIC, "GnuTLS init failed: %s "
-              "priority table overflow", which);
-            return FALSE;
-            }
-          }
-        }
-      }
+    DEBUG(D_tls) debug_printf("GnuTLS session cipher/priority \"%s\"\n",
+        state->exp_tls_require_ciphers);
+
+    rc = gnutls_priority_init(&state->priority_cache,
+        CS state->exp_tls_require_ciphers, &errpos);
+    want_default_priorities = FALSE;
+    p = state->exp_tls_require_ciphers;
     }
   }
+if (want_default_priorities)
+  {
+  rc = gnutls_priority_init(&state->priority_cache,
+      exim_default_gnutls_priority, &errpos);
+  p = US exim_default_gnutls_priority;
+  }
 
-DEBUG(D_tls)
+exim_gnutls_err_check(string_sprintf(
+      "gnutls_priority_init(%s) failed at offset %ld, \"%.6s..\"",
+      p, errpos - CS p, errpos));
+
+rc = gnutls_priority_set(state->session, state->priority_cache);
+exim_gnutls_err_check(US"gnutls_priority_set");
+
+gnutls_db_set_cache_expiration(state->session, ssl_session_timeout);
+
+/* Reduce security in favour of increased compatibility, if the admin
+decides to make that trade-off. */
+if (gnutls_compat_mode)
   {
-  int *ptr = plist;
-  debug_printf("adjusted %s priorities:", which);
-  while (*ptr != 0) debug_printf(" %d", *ptr++);
-  debug_printf("\n");
+#if LIBGNUTLS_VERSION_NUMBER >= 0x020104
+  DEBUG(D_tls) debug_printf("lowering GnuTLS security, compatibility mode\n");
+  gnutls_session_enable_compatibility_mode(state->session);
+#else
+  DEBUG(D_tls) debug_printf("Unable to set gnutls_compat_mode - GnuTLS version too old\n");
+#endif
   }
 
-return TRUE;
+*caller_state = state;
+/* needs to happen before callbacks during handshake */
+current_global_tls_state = state;
+return OK;
 }
 
 
 
 
 /*************************************************
-*        Initialize a single GNUTLS session      *
+*            Extract peer information            *
 *************************************************/
 
-/* Set the algorithm, the db backend, whether to request certificates etc.
-
-TLS in Exim was first implemented using OpenSSL. This has a function to which
-you pass a list of cipher suites that are permitted/not permitted. GnuTLS works
-differently. It operates using priority lists for the different components of
-cipher suites.
-
-For compatibility of configuration, we scan a list of cipher suites and set
-priorities therefrom. However, at the moment, we pay attention only to the bulk
-cipher.
+/* Called from both server and client code.
+Only this is allowed to set state->peerdn and we use that to detect double-calls.
 
 Arguments:
-  side         one of GNUTLS_SERVER, GNUTLS_CLIENT
-  expciphers   expanded ciphers list or NULL
-  expmac       expanded MAC list or NULL
-  expkx        expanded key-exchange list or NULL
-  expproto     expanded protocol list or NULL
+  state           exim_gnutls_state_st *
 
-Returns:  a gnutls_session, or NULL if there is a problem
+Returns:          OK/DEFER/FAIL
 */
 
-static gnutls_session
-tls_session_init(int side, uschar *expciphers, uschar *expmac, uschar *expkx,
-  uschar *expproto)
+static int
+peer_status(exim_gnutls_state_st *state)
 {
-gnutls_session session;
+const gnutls_datum *cert_list;
+int rc;
+unsigned int cert_list_size = 0;
+gnutls_certificate_type_t ct;
+gnutls_x509_crt_t crt;
+uschar *dn_buf;
+size_t sz;
 
-gnutls_init(&session, side);
+if (state->peerdn)
+  return OK;
 
-/* Initialize the lists of permitted protocols, key-exchange methods, ciphers,
-and MACs. */
+state->peerdn = US"unknown";
 
-memcpy(cipher_priority, default_cipher_priority, sizeof(cipher_priority));
-memcpy(mac_priority, default_mac_priority, sizeof(mac_priority));
-memcpy(kx_priority, default_kx_priority, sizeof(kx_priority));
-memcpy(proto_priority, default_proto_priority, sizeof(proto_priority));
+cert_list = gnutls_certificate_get_peers(state->session, &cert_list_size);
 
-/* The names OpenSSL uses in tls_require_ciphers are of the form DES-CBC3-SHA,
-using hyphen separators. GnuTLS uses underscore separators. So that I can use
-either form for tls_require_ciphers in my tests, and also for general
-convenience, we turn hyphens into underscores before scanning the list. */
+if (cert_list == NULL || cert_list_size == 0)
+  {
+  state->peerdn = US"unknown (no certificate)";
+  DEBUG(D_tls) debug_printf("TLS: no certificate from peer (%p & %d)\n",
+      cert_list, cert_list_size);
+  if (state->verify_requirement == VERIFY_REQUIRED)
+    return tls_error(US"certificate verification failed",
+        "no certificate received from peer", state->host);
+  return OK;
+  }
 
-if (expciphers != NULL)
+ct = gnutls_certificate_type_get(state->session);
+if (ct != GNUTLS_CRT_X509)
   {
-  uschar *s = expciphers;
-  while (*s != 0) { if (*s == '-') *s = '_'; s++; }
+  const char *ctn = gnutls_certificate_type_get_name(ct);
+  state->peerdn = string_sprintf("unknown (type %s)", ctn);
+  DEBUG(D_tls)
+    debug_printf("TLS: peer cert not X.509 but instead \"%s\"\n", ctn);
+  if (state->verify_requirement == VERIFY_REQUIRED)
+    return tls_error(US"certificate verification not possible, unhandled type",
+        ctn, state->host);
+  return OK;
   }
 
-if ((expciphers != NULL &&
-      !set_priority(cipher_priority, sizeof(cipher_priority)/sizeof(int),
-        expciphers, cipher_index, sizeof(cipher_index)/sizeof(pri_item),
-        US"cipher")) ||
-    (expmac != NULL &&
-      !set_priority(mac_priority, sizeof(mac_priority)/sizeof(int),
-        expmac, mac_index, sizeof(mac_index)/sizeof(pri_item),
-        US"MAC")) ||
-    (expkx != NULL &&
-      !set_priority(kx_priority, sizeof(kx_priority)/sizeof(int),
-        expkx, kx_index, sizeof(kx_index)/sizeof(pri_item),
-        US"key-exchange")) ||
-    (expproto != NULL &&
-      !set_priority(proto_priority, sizeof(proto_priority)/sizeof(int),
-        expproto, proto_index, sizeof(proto_index)/sizeof(pri_item),
-        US"protocol")))
+#define exim_gnutls_peer_err(Label) do { \
+  if (rc != GNUTLS_E_SUCCESS) { \
+    DEBUG(D_tls) debug_printf("TLS: peer cert problem: %s: %s\n", (Label), gnutls_strerror(rc)); \
+    if (state->verify_requirement == VERIFY_REQUIRED) { return tls_error((Label), gnutls_strerror(rc), state->host); } \
+    return OK; } } while (0)
+
+rc = gnutls_x509_crt_init(&crt);
+exim_gnutls_peer_err(US"gnutls_x509_crt_init (crt)");
+
+rc = gnutls_x509_crt_import(crt, &cert_list[0], GNUTLS_X509_FMT_DER);
+exim_gnutls_peer_err(US"failed to import certificate [gnutls_x509_crt_import(cert 0)]");
+sz = 0;
+rc = gnutls_x509_crt_get_dn(crt, NULL, &sz);
+if (rc != GNUTLS_E_SHORT_MEMORY_BUFFER)
   {
-  gnutls_deinit(session);
-  return NULL;
+  exim_gnutls_peer_err(US"getting size for cert DN failed");
+  return FAIL; /* should not happen */
   }
+dn_buf = store_get_perm(sz);
+rc = gnutls_x509_crt_get_dn(crt, CS dn_buf, &sz);
+exim_gnutls_peer_err(US"failed to extract certificate DN [gnutls_x509_crt_get_dn(cert 0)]");
+state->peerdn = dn_buf;
+
+return OK;
+#undef exim_gnutls_peer_err
+}
 
-/* Define the various priorities */
 
-gnutls_cipher_set_priority(session, cipher_priority);
-gnutls_compression_set_priority(session, comp_priority);
-gnutls_kx_set_priority(session, kx_priority);
-gnutls_protocol_set_priority(session, proto_priority);
-gnutls_mac_set_priority(session, mac_priority);
 
-gnutls_cred_set(session, GNUTLS_CRD_CERTIFICATE, x509_cred);
 
-gnutls_dh_set_prime_bits(session, DH_BITS);
+/*************************************************
+*            Verify peer certificate             *
+*************************************************/
 
-/* Request or demand a certificate of the peer, as configured. This will
-happen only in a server. */
+/* Called from both server and client code.
+*Should* be using a callback registered with
+gnutls_certificate_set_verify_function() to fail the handshake if we dislike
+the peer information, but that's too new for some OSes.
 
-if (verify_requirement != VERIFY_NONE)
-  gnutls_certificate_server_set_request(session,
-    (verify_requirement == VERIFY_OPTIONAL)?
-      GNUTLS_CERT_REQUEST : GNUTLS_CERT_REQUIRE);
+Arguments:
+  state           exim_gnutls_state_st *
+  error           where to put an error message
 
-gnutls_db_set_cache_expiration(session, ssl_session_timeout);
+Returns:
+  FALSE     if the session should be rejected
+  TRUE      if the cert is okay or we just don't care
+*/
 
-/* Reduce security in favour of increased compatibility, if the admin
-decides to make that trade-off. */
-if (gnutls_compat_mode)
+static BOOL
+verify_certificate(exim_gnutls_state_st *state, const char **error)
+{
+int rc;
+unsigned int verify;
+
+*error = NULL;
+
+rc = peer_status(state);
+if (rc != OK)
   {
-#if LIBGNUTLS_VERSION_NUMBER >= 0x020104
-  DEBUG(D_tls) debug_printf("lowering GnuTLS security, compatibility mode\n");
-  gnutls_session_enable_compatibility_mode(session);
-#else
-  DEBUG(D_tls) debug_printf("Unable to set gnutls_compat_mode - GnuTLS version too old\n");
-#endif
+  verify = GNUTLS_CERT_INVALID;
+  *error = "not supplied";
+  }
+else
+  {
+  rc = gnutls_certificate_verify_peers2(state->session, &verify);
   }
 
-DEBUG(D_tls) debug_printf("initialized GnuTLS session\n");
-return session;
-}
+/* Handle the result of verification. INVALID seems to be set as well
+as REVOKED, but leave the test for both. */
 
+if ((rc < 0) || (verify & (GNUTLS_CERT_INVALID|GNUTLS_CERT_REVOKED)) != 0)
+  {
+  state->peer_cert_verified = FALSE;
+  if (*error == NULL)
+    *error = ((verify & GNUTLS_CERT_REVOKED) != 0) ? "revoked" : "invalid";
 
+  DEBUG(D_tls)
+    debug_printf("TLS certificate verification failed (%s): peerdn=%s\n",
+        *error, state->peerdn);
 
-/*************************************************
-*           Get name of cipher in use            *
-*************************************************/
+  if (state->verify_requirement == VERIFY_REQUIRED)
+    {
+    gnutls_alert_send(state->session, GNUTLS_AL_FATAL, GNUTLS_A_BAD_CERTIFICATE);
+    return FALSE;
+    }
+  DEBUG(D_tls)
+    debug_printf("TLS verify failure overriden (host in tls_try_verify_hosts)\n");
+  }
+else
+  {
+  state->peer_cert_verified = TRUE;
+  DEBUG(D_tls) debug_printf("TLS certificate verified: peerdn=%s\n", state->peerdn);
+  }
 
-/* The answer is left in a static buffer, and tls_cipher is set to point
-to it.
+tls_peerdn = state->peerdn;
 
-Argument:   pointer to a GnuTLS session
-Returns:    nothing
-*/
+return TRUE;
+}
 
+
+
+
+/* ------------------------------------------------------------------------ */
+/* Callbacks */
+
+/* Logging function which can be registered with
+ *   gnutls_global_set_log_function()
+ *   gnutls_global_set_log_level() 0..9
+ */
 static void
-construct_cipher_name(gnutls_session session)
+exim_gnutls_logger_cb(int level, const char *message)
 {
-static uschar cipherbuf[256];
-uschar *ver;
-int c, kx, mac;
-#ifdef GNUTLS_CB_TLS_UNIQUE
-int rc;
-gnutls_datum_t channel;
-#endif
+  DEBUG(D_tls) debug_printf("GnuTLS<%d>: %s\n", level, message);
+}
 
-ver = string_copy(
-  US gnutls_protocol_get_name(gnutls_protocol_get_version(session)));
-if (Ustrncmp(ver, "TLS ", 4) == 0) ver[3] = '-';   /* Don't want space */
 
-c = gnutls_cipher_get(session);
-/* returns size in "bytes" */
-tls_bits = gnutls_cipher_get_key_size(c) * 8;
+/* Called after client hello, should handle SNI work.
+This will always set tls_sni (state->received_sni) if available,
+and may trigger presenting different certificates,
+if state->trigger_sni_changes is TRUE.
 
-mac = gnutls_mac_get(session);
-kx = gnutls_kx_get(session);
+Should be registered with
+  gnutls_handshake_set_post_client_hello_function()
 
-string_format(cipherbuf, sizeof(cipherbuf), "%s:%s:%u", ver,
-  gnutls_cipher_suite_get_name(kx, c, mac), tls_bits);
-tls_cipher = cipherbuf;
+"This callback must return 0 on success or a gnutls error code to terminate the
+handshake.".
 
-DEBUG(D_tls) debug_printf("cipher: %s\n", cipherbuf);
+For inability to get SNI information, we return 0.
+We only return non-zero if re-setup failed.
+*/
 
-if (tls_channelbinding_b64)
-  free(tls_channelbinding_b64);
-tls_channelbinding_b64 = NULL;
+static int
+exim_sni_handling_cb(gnutls_session_t session)
+{
+char sni_name[MAX_HOST_LEN];
+size_t data_len = MAX_HOST_LEN;
+exim_gnutls_state_st *state = current_global_tls_state;
+unsigned int sni_type;
+int rc, old_pool;
+
+rc = gnutls_server_name_get(session, sni_name, &data_len, &sni_type, 0);
+exim_gnutls_err_debugreturn0("gnutls_server_name_get()");
+if (sni_type != GNUTLS_NAME_DNS)
+  {
+  DEBUG(D_tls) debug_printf("TLS: ignoring SNI of unhandled type %u\n", sni_type);
+  return 0;
+  }
 
-#ifdef GNUTLS_CB_TLS_UNIQUE
-channel = { NULL, 0 };
-rc = gnutls_session_channel_binding(session, GNUTLS_CB_TLS_UNIQUE, &channel);
-if (rc) {
-  DEBUG(D_tls) debug_printf("Channel binding error: %s\n", gnutls_strerror(rc));
-} else {
-  tls_channelbinding_b64 = auth_b64encode(channel.data, (int)channel.size);
-  DEBUG(D_tls) debug_printf("Have channel bindings cached for possible auth usage.\n");
-}
-#endif
+/* We now have a UTF-8 string in sni_name */
+old_pool = store_pool;
+store_pool = POOL_PERM;
+state->received_sni = string_copyn(US sni_name, data_len);
+store_pool = old_pool;
+
+/* We set this one now so that variable expansions below will work */
+tls_sni = state->received_sni;
+
+DEBUG(D_tls) debug_printf("Received TLS SNI \"%s\"%s\n", sni_name,
+    state->trigger_sni_changes ? "" : " (unused for certificate selection)");
+
+if (!state->trigger_sni_changes)
+  return 0;
+
+rc = tls_expand_session_files(state);
+if (rc != OK)
+  {
+  /* If the setup of certs/etc failed before handshake, TLS would not have
+  been offered.  The best we can do now is abort. */
+  return GNUTLS_E_APPLICATION_ERROR_MIN;
+  }
+
+rc = gnutls_credentials_set(state->session, GNUTLS_CRD_CERTIFICATE, state->x509_cred);
+return (rc == GNUTLS_E_SUCCESS) ? 0 : rc;
 }
 
 
 
+
+/* ------------------------------------------------------------------------ */
+/* Exported functions */
+
+
+
+
 /*************************************************
 *       Start a TLS session in a server          *
 *************************************************/
@@ -905,9 +1180,6 @@ a TLS session.
 
 Arguments:
   require_ciphers  list of allowed ciphers or NULL
-  require_mac      list of allowed MACs or NULL
-  require_kx       list of allowed key_exchange methods or NULL
-  require_proto    list of allowed protocols or NULL
 
 Returns:           OK on success
                    DEFER for errors before the start of the negotiation
@@ -916,21 +1188,18 @@ Returns:           OK on success
 */
 
 int
-tls_server_start(uschar *require_ciphers, uschar *require_mac,
-  uschar *require_kx, uschar *require_proto)
+tls_server_start(const uschar *require_ciphers)
 {
 int rc;
 const char *error;
-uschar *expciphers = NULL;
-uschar *expmac = NULL;
-uschar *expkx = NULL;
-uschar *expproto = NULL;
+exim_gnutls_state_st *state = NULL;
 
 /* Check for previous activation */
+/* nb: this will not be TLS callout safe, needs reworking as part of that. */
 
 if (tls_active >= 0)
   {
-  tls_error("STARTTLS received after TLS started", NULL, "");
+  tls_error(US"STARTTLS received after TLS started", "", NULL);
   smtp_printf("554 Already in TLS\r\n");
   return FAIL;
   }
@@ -938,36 +1207,40 @@ if (tls_active >= 0)
 /* Initialize the library. If it fails, it will already have logged the error
 and sent an SMTP response. */
 
-DEBUG(D_tls) debug_printf("initializing GnuTLS as a server\n");
+DEBUG(D_tls) debug_printf("initialising GnuTLS as a server\n");
 
-rc = tls_init(NULL, tls_certificate, tls_privatekey, tls_verify_certificates,
-  tls_crl);
+rc = tls_init(NULL, tls_certificate, tls_privatekey,
+    NULL, tls_verify_certificates, tls_crl,
+    require_ciphers, &state);
 if (rc != OK) return rc;
 
-if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers) ||
-    !expand_check(require_mac, US"gnutls_require_mac", &expmac) ||
-    !expand_check(require_kx, US"gnutls_require_kx", &expkx) ||
-    !expand_check(require_proto, US"gnutls_require_proto", &expproto))
-  return FAIL;
-
 /* If this is a host for which certificate verification is mandatory or
 optional, set up appropriately. */
 
-tls_certificate_verified = FALSE;
-verify_requirement = VERIFY_NONE;
-
 if (verify_check_host(&tls_verify_hosts) == OK)
-  verify_requirement = VERIFY_REQUIRED;
+  {
+  DEBUG(D_tls) debug_printf("TLS: a client certificate will be required.\n");
+  state->verify_requirement = VERIFY_REQUIRED;
+  gnutls_certificate_server_set_request(state->session, GNUTLS_CERT_REQUIRE);
+  }
 else if (verify_check_host(&tls_try_verify_hosts) == OK)
-  verify_requirement = VERIFY_OPTIONAL;
+  {
+  DEBUG(D_tls) debug_printf("TLS: a client certificate will be requested but not required.\n");
+  state->verify_requirement = VERIFY_OPTIONAL;
+  gnutls_certificate_server_set_request(state->session, GNUTLS_CERT_REQUEST);
+  }
+else
+  {
+  DEBUG(D_tls) debug_printf("TLS: a client certificate will not be requested.\n");
+  state->verify_requirement = VERIFY_NONE;
+  gnutls_certificate_server_set_request(state->session, GNUTLS_CERT_IGNORE);
+  }
 
-/* Prepare for new connection */
+/* Register SNI handling; always, even if not in tls_certificate, so that the
+expansion variable $tls_sni is always available. */
 
-tls_session = tls_session_init(GNUTLS_SERVER, expciphers, expmac, expkx,
-  expproto);
-if (tls_session == NULL)
-  return tls_error(US"tls_session_init", NULL,
-    gnutls_strerror(GNUTLS_E_MEMORY_ERROR));
+gnutls_handshake_set_post_client_hello_function(state->session,
+    exim_sni_handling_cb);
 
 /* Set context and tell client to go ahead, except in the case of TLS startup
 on connection, where outputting anything now upsets the clients and tends to
@@ -984,19 +1257,24 @@ if (!tls_on_connect)
 /* Now negotiate the TLS session. We put our own timer on it, since it seems
 that the GnuTLS library doesn't. */
 
-gnutls_transport_set_ptr2(tls_session, (gnutls_transport_ptr)fileno(smtp_in),
-                                       (gnutls_transport_ptr)fileno(smtp_out));
+gnutls_transport_set_ptr2(state->session,
+    (gnutls_transport_ptr)fileno(smtp_in),
+    (gnutls_transport_ptr)fileno(smtp_out));
+state->fd_in = fileno(smtp_in);
+state->fd_out = fileno(smtp_out);
 
 sigalrm_seen = FALSE;
 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
-rc = gnutls_handshake(tls_session);
+do
+  {
+  rc = gnutls_handshake(state->session);
+  } while ((rc == GNUTLS_E_AGAIN) || (rc == GNUTLS_E_INTERRUPTED));
 alarm(0);
 
-if (rc < 0)
+if (rc != GNUTLS_E_SUCCESS)
   {
-  tls_error(US"gnutls_handshake", NULL,
-    sigalrm_seen ? "timed out" : gnutls_strerror(rc));
-
+  tls_error(US"gnutls_handshake",
+      sigalrm_seen ? "timed out" : gnutls_strerror(rc), NULL);
   /* It seems that, except in the case of a timeout, we have to close the
   connection right here; otherwise if the other end is running OpenSSL it hangs
   until the server times out. */
@@ -1012,21 +1290,39 @@ if (rc < 0)
 
 DEBUG(D_tls) debug_printf("gnutls_handshake was successful\n");
 
-if (verify_requirement != VERIFY_NONE &&
-     !verify_certificate(tls_session, &error))
+/* Verify after the fact */
+
+if (state->verify_requirement != VERIFY_NONE)
   {
-  tls_error(US"certificate verification failed", NULL, error);
-  return FAIL;
+  if (!verify_certificate(state, &error))
+    {
+    if (state->verify_requirement == VERIFY_OPTIONAL)
+      {
+      DEBUG(D_tls)
+        debug_printf("TLS: continuing on only because verification was optional, after: %s\n",
+            error);
+      }
+    else
+      {
+      tls_error(US"certificate verification failed", error, NULL);
+      return FAIL;
+      }
+    }
   }
 
-construct_cipher_name(tls_session);
+/* Figure out peer DN, and if authenticated, etc. */
+
+rc = peer_status(state);
+if (rc != OK) return rc;
+
+/* Sets various Exim expansion variables; always safe within server */
+
+extract_exim_vars_from_tls_state(state);
 
 /* TLS has been set up. Adjust the input functions to read via TLS,
 and initialize appropriately. */
 
-ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
-ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
-ssl_xfer_eof = ssl_xfer_error = 0;
+state->xfer_buffer = store_malloc(ssl_xfer_buffer_size);
 
 receive_getc = tls_getc;
 receive_ungetc = tls_ungetc;
@@ -1034,8 +1330,6 @@ receive_feof = tls_feof;
 receive_ferror = tls_ferror;
 receive_smtp_buffered = tls_smtp_buffered;
 
-tls_active = fileno(smtp_out);
-
 return OK;
 }
 
@@ -1052,16 +1346,13 @@ Arguments:
   fd                the fd of the connection
   host              connected host (for messages)
   addr              the first address (not used)
-  dhparam           DH parameter file
+  dhparam           DH parameter file (ignored, we're a client)
   certificate       certificate file
   privatekey        private key file
   sni               TLS SNI to send to remote host
   verify_certs      file for certificate verify
   verify_crl        CRL for verify
   require_ciphers   list of allowed ciphers or NULL
-  require_mac       list of allowed MACs or NULL
-  require_kx        list of allowed key_exchange methods or NULL
-  require_proto     list of allowed protocols or NULL
   timeout           startup timeout
 
 Returns:            OK/DEFER/FAIL (because using common functions),
@@ -1069,114 +1360,116 @@ Returns:            OK/DEFER/FAIL (because using common functions),
 */
 
 int
-tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam,
-  uschar *certificate, uschar *privatekey, uschar *sni ARG_UNUSED,
-  uschar *verify_certs, uschar *verify_crl,
-  uschar *require_ciphers, uschar *require_mac,
-  uschar *require_kx, uschar *require_proto, int timeout)
+tls_client_start(int fd, host_item *host,
+    address_item *addr ARG_UNUSED, uschar *dhparam ARG_UNUSED,
+    uschar *certificate, uschar *privatekey, uschar *sni,
+    uschar *verify_certs, uschar *verify_crl,
+    uschar *require_ciphers, int timeout)
 {
-const gnutls_datum *server_certs;
-uschar *expciphers = NULL;
-uschar *expmac = NULL;
-uschar *expkx = NULL;
-uschar *expproto = NULL;
-const char *error;
-unsigned int server_certs_size;
 int rc;
+const char *error;
+exim_gnutls_state_st *state = NULL;
 
-DEBUG(D_tls) debug_printf("initializing GnuTLS as a client\n");
+DEBUG(D_tls) debug_printf("initialising GnuTLS as a client on fd %d\n", fd);
 
-verify_requirement = (verify_certs == NULL)? VERIFY_NONE : VERIFY_REQUIRED;
-rc = tls_init(host, certificate, privatekey, verify_certs, verify_crl);
+rc = tls_init(host, certificate, privatekey,
+    sni, verify_certs, verify_crl, require_ciphers, &state);
 if (rc != OK) return rc;
 
-if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers) ||
-    !expand_check(require_mac, US"gnutls_require_mac", &expmac) ||
-    !expand_check(require_kx, US"gnutls_require_kx", &expkx) ||
-    !expand_check(require_proto, US"gnutls_require_proto", &expproto))
-  return FAIL;
-
-tls_session = tls_session_init(GNUTLS_CLIENT, expciphers, expmac, expkx,
-  expproto);
+gnutls_dh_set_prime_bits(state->session, EXIM_CLIENT_DH_MIN_BITS);
 
-if (tls_session == NULL)
-  return tls_error(US "tls_session_init", host,
-    gnutls_strerror(GNUTLS_E_MEMORY_ERROR));
+if (verify_certs == NULL)
+  {
+  DEBUG(D_tls) debug_printf("TLS: server certificate verification not required\n");
+  state->verify_requirement = VERIFY_NONE;
+  /* we still ask for it, to log it, etc */
+  gnutls_certificate_server_set_request(state->session, GNUTLS_CERT_REQUEST);
+  }
+else
+  {
+  DEBUG(D_tls) debug_printf("TLS: server certificate verification required\n");
+  state->verify_requirement = VERIFY_REQUIRED;
+  gnutls_certificate_server_set_request(state->session, GNUTLS_CERT_REQUIRE);
+  }
 
-gnutls_transport_set_ptr(tls_session, (gnutls_transport_ptr)fd);
+gnutls_transport_set_ptr(state->session, (gnutls_transport_ptr)fd);
+state->fd_in = fd;
+state->fd_out = fd;
 
 /* There doesn't seem to be a built-in timeout on connection. */
 
 sigalrm_seen = FALSE;
 alarm(timeout);
-rc = gnutls_handshake(tls_session);
+do
+  {
+  rc = gnutls_handshake(state->session);
+  } while ((rc == GNUTLS_E_AGAIN) || (rc == GNUTLS_E_INTERRUPTED));
 alarm(0);
 
-if (rc < 0)
-  return tls_error(US "gnutls_handshake", host,
-    sigalrm_seen ? "timed out" : gnutls_strerror(rc));
+DEBUG(D_tls) debug_printf("gnutls_handshake was successful\n");
 
-server_certs = gnutls_certificate_get_peers(tls_session, &server_certs_size);
+/* Verify late */
 
-if (server_certs != NULL)
-  {
-  uschar buff[1024];
-  gnutls_x509_crt gcert;
+if (state->verify_requirement != VERIFY_NONE &&
+    !verify_certificate(state, &error))
+  return tls_error(US"certificate verification failed", error, state->host);
 
-  gnutls_x509_crt_init(&gcert);
-  tls_peerdn = US"unknown";
+/* Figure out peer DN, and if authenticated, etc. */
 
-  if (gnutls_x509_crt_import(gcert, server_certs, GNUTLS_X509_FMT_DER) == 0)
-    {
-    size_t bufsize = sizeof(buff);
-    if (gnutls_x509_crt_get_dn(gcert, CS buff, &bufsize) >= 0)
-      tls_peerdn = string_copy_malloc(buff);
-    }
-  }
+rc = peer_status(state);
+if (rc != OK) return rc;
 
-/* Should we also verify the hostname here? */
+/* Sets various Exim expansion variables; always safe within server */
 
-if (verify_requirement != VERIFY_NONE &&
-      !verify_certificate(tls_session, &error))
-  return tls_error(US"certificate verification failed", host, error);
+extract_exim_vars_from_tls_state(state);
 
-construct_cipher_name(tls_session);    /* Sets tls_cipher */
-tls_active = fd;
 return OK;
 }
 
 
 
+
 /*************************************************
-*    Deal with logging errors during I/O         *
+*         Close down a TLS session               *
 *************************************************/
 
-/* We have to get the identity of the peer from saved data.
-
-Argument:
-  ec       the GnuTLS error code, or 0 if it's a local error
-  when     text identifying read or write
-  text     local error text when ec is 0
+/* This is also called from within a delivery subprocess forked from the
+daemon, to shut down the TLS library, without actually doing a shutdown (which
+would tamper with the TLS session in the parent process).
 
-Returns:   nothing
+Arguments:   TRUE if gnutls_bye is to be called
+Returns:     nothing
 */
 
-static void
-record_io_error(int ec, uschar *when, uschar *text)
+void
+tls_close(BOOL shutdown)
 {
-const char *msg;
+exim_gnutls_state_st *state = current_global_tls_state;
 
-if (ec == GNUTLS_E_FATAL_ALERT_RECEIVED)
-  msg = string_sprintf("%s: %s", gnutls_strerror(ec),
-    gnutls_alert_get_name(gnutls_alert_get(tls_session)));
-else
-  msg = gnutls_strerror(ec);
+if (tls_active < 0) return;  /* TLS was not active */
+
+if (shutdown)
+  {
+  DEBUG(D_tls) debug_printf("tls_close(): shutting down TLS\n");
+  gnutls_bye(state->session, GNUTLS_SHUT_WR);
+  }
+
+gnutls_deinit(state->session);
+
+memcpy(state, &exim_gnutls_state_init, sizeof(exim_gnutls_state_init));
+
+if ((state_server.session == NULL) && (state_client.session == NULL))
+  {
+  gnutls_global_deinit();
+  exim_gnutls_base_init_done = FALSE;
+  }
 
-tls_error(when, client_host, msg);
+tls_active = -1;
 }
 
 
 
+
 /*************************************************
 *            TLS version of getc                 *
 *************************************************/
@@ -1184,6 +1477,8 @@ tls_error(when, client_host, msg);
 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
 it refills the buffer via the GnuTLS reading function.
 
+This feeds DKIM and should be used for all message-body reads.
+
 Arguments:  none
 Returns:    the next character or EOF
 */
@@ -1191,15 +1486,16 @@ Returns:    the next character or EOF
 int
 tls_getc(void)
 {
-if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
+exim_gnutls_state_st *state = current_global_tls_state;
+if (state->xfer_buffer_lwm >= state->xfer_buffer_hwm)
   {
-  int inbytes;
+  ssize_t inbytes;
 
-  DEBUG(D_tls) debug_printf("Calling gnutls_record_recv(%lx, %lx, %u)\n",
-    (long) tls_session, (long) ssl_xfer_buffer, ssl_xfer_buffer_size);
+  DEBUG(D_tls) debug_printf("Calling gnutls_record_recv(%p, %p, %u)\n",
+    state->session, state->xfer_buffer, ssl_xfer_buffer_size);
 
   if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
-  inbytes = gnutls_record_recv(tls_session, CS ssl_xfer_buffer,
+  inbytes = gnutls_record_recv(state->session, state->xfer_buffer,
     ssl_xfer_buffer_size);
   alarm(0);
 
@@ -1217,9 +1513,12 @@ if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
     receive_ferror = smtp_ferror;
     receive_smtp_buffered = smtp_buffered;
 
-    gnutls_deinit(tls_session);
-    tls_session = NULL;
+    gnutls_deinit(state->session);
+    state->session = NULL;
     tls_active = -1;
+    tls_bits = 0;
+    tls_certificate_verified = FALSE;
+    tls_channelbinding_b64 = NULL;
     tls_cipher = NULL;
     tls_peerdn = NULL;
 
@@ -1230,30 +1529,31 @@ if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
 
   else if (inbytes < 0)
     {
-    record_io_error(inbytes, US"recv", NULL);
-    ssl_xfer_error = 1;
+    record_io_error(state, (int) inbytes, US"recv", NULL);
+    state->xfer_error = 1;
     return EOF;
     }
 #ifndef DISABLE_DKIM
-  dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
+  dkim_exim_verify_feed(state->xfer_buffer, inbytes);
 #endif
-  ssl_xfer_buffer_hwm = inbytes;
-  ssl_xfer_buffer_lwm = 0;
+  state->xfer_buffer_hwm = (int) inbytes;
+  state->xfer_buffer_lwm = 0;
   }
 
-
 /* Something in the buffer; return next uschar */
 
-return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
+return state->xfer_buffer[state->xfer_buffer_lwm++];
 }
 
 
 
+
 /*************************************************
 *          Read bytes from TLS channel           *
 *************************************************/
 
-/*
+/* This does not feed DKIM, so if the caller uses this for reading message body,
+then the caller must feed DKIM.
 Arguments:
   buff      buffer of data
   len       size of buffer
@@ -1265,24 +1565,36 @@ Returns:    the number of bytes read
 int
 tls_read(uschar *buff, size_t len)
 {
-int inbytes;
+exim_gnutls_state_st *state = current_global_tls_state;
+ssize_t inbytes;
 
-DEBUG(D_tls) debug_printf("Calling gnutls_record_recv(%lx, %lx, %u)\n",
-  (long) tls_session, (long) buff, len);
+if (len > INT_MAX)
+  len = INT_MAX;
 
-inbytes = gnutls_record_recv(tls_session, CS buff, len);
+if (state->xfer_buffer_lwm < state->xfer_buffer_hwm)
+  DEBUG(D_tls)
+    debug_printf("*** PROBABLY A BUG *** " \
+        "tls_read() called with data in the tls_getc() buffer, %d ignored\n",
+        state->xfer_buffer_hwm - state->xfer_buffer_lwm);
+
+DEBUG(D_tls)
+  debug_printf("Calling gnutls_record_recv(%p, %p, " SIZE_T_FMT ")\n",
+      state->session, buff, len);
+
+inbytes = gnutls_record_recv(state->session, buff, len);
 if (inbytes > 0) return inbytes;
 if (inbytes == 0)
   {
   DEBUG(D_tls) debug_printf("Got TLS_EOF\n");
   }
-else record_io_error(inbytes, US"recv", NULL);
+else record_io_error(state, (int)inbytes, US"recv", NULL);
 
 return -1;
 }
 
 
 
+
 /*************************************************
 *         Write bytes down TLS channel           *
 *************************************************/
@@ -1299,25 +1611,26 @@ Returns:    the number of bytes after a successful write,
 int
 tls_write(const uschar *buff, size_t len)
 {
-int outbytes;
-int left = len;
+ssize_t outbytes;
+size_t left = len;
+exim_gnutls_state_st *state = current_global_tls_state;
 
-DEBUG(D_tls) debug_printf("tls_do_write(%lx, %d)\n", (long) buff, left);
+DEBUG(D_tls) debug_printf("tls_do_write(%p, " SIZE_T_FMT ")\n", buff, left);
 while (left > 0)
   {
-  DEBUG(D_tls) debug_printf("gnutls_record_send(SSL, %lx, %d)\n", (long)buff,
-    left);
-  outbytes = gnutls_record_send(tls_session, CS buff, left);
+  DEBUG(D_tls) debug_printf("gnutls_record_send(SSL, %p, " SIZE_T_FMT ")\n",
+      buff, left);
+  outbytes = gnutls_record_send(state->session, buff, left);
 
-  DEBUG(D_tls) debug_printf("outbytes=%d\n", outbytes);
+  DEBUG(D_tls) debug_printf("outbytes=" SSIZE_T_FMT "\n", outbytes);
   if (outbytes < 0)
     {
-    record_io_error(outbytes, US"send", NULL);
+    record_io_error(state, outbytes, US"send", NULL);
     return -1;
     }
   if (outbytes == 0)
     {
-    record_io_error(0, US"send", US"TLS channel closed on write");
+    record_io_error(state, 0, US"send", US"TLS channel closed on write");
     return -1;
     }
 
@@ -1325,39 +1638,71 @@ while (left > 0)
   buff += outbytes;
   }
 
-return len;
+if (len > INT_MAX)
+  {
+  DEBUG(D_tls)
+    debug_printf("Whoops!  Wrote more bytes (" SIZE_T_FMT ") than INT_MAX\n",
+        len);
+  len = INT_MAX;
+  }
+
+return (int) len;
 }
 
 
 
+
 /*************************************************
-*         Close down a TLS session               *
+*            Random number generation            *
 *************************************************/
 
-/* This is also called from within a delivery subprocess forked from the
-daemon, to shut down the TLS library, without actually doing a shutdown (which
-would tamper with the TLS session in the parent process).
+/* Pseudo-random number generation.  The result is not expected to be
+cryptographically strong but not so weak that someone will shoot themselves
+in the foot using it as a nonce in input in some email header scheme or
+whatever weirdness they'll twist this into.  The result should handle fork()
+and avoid repeating sequences.  OpenSSL handles that for us.
 
-Arguments:   TRUE if gnutls_bye is to be called
-Returns:     nothing
+Arguments:
+  max       range maximum
+Returns     a random number in range [0, max-1]
 */
 
-void
-tls_close(BOOL shutdown)
+int
+vaguely_random_number(int max)
 {
-if (tls_active < 0) return;  /* TLS was not active */
-
-if (shutdown)
+unsigned int r;
+int i, needed_len;
+uschar *p;
+uschar smallbuf[sizeof(r)];
+
+if (max <= 1)
+  return 0;
+
+needed_len = sizeof(r);
+/* Don't take 8 times more entropy than needed if int is 8 octets and we were
+ * asked for a number less than 10. */
+for (r = max, i = 0; r; ++i)
+  r >>= 1;
+i = (i + 7) / 8;
+if (i < needed_len)
+  needed_len = i;
+
+i = gnutls_rnd(GNUTLS_RND_NONCE, smallbuf, needed_len);
+if (i < 0)
   {
-  DEBUG(D_tls) debug_printf("tls_close(): shutting down TLS\n");
-  gnutls_bye(tls_session, GNUTLS_SHUT_WR);
+  DEBUG(D_all) debug_printf("gnutls_rnd() failed, using fallback.\n");
+  return vaguely_random_number_fallback(max);
+  }
+r = 0;
+for (p = smallbuf; needed_len; --needed_len, ++p)
+  {
+  r *= 256;
+  r += *p;
   }
 
-gnutls_deinit(tls_session);
-tls_session = NULL;
-gnutls_global_deinit();
-
-tls_active = -1;
+/* We don't particularly care about weighted results; if someone wants
+ * smooth distribution and cares enough then they should submit a patch then. */
+return r % max;
 }
 
 
diff --git a/src/src/tls-openssl.c b/src/src/tls-openssl.c
index e609670ee..316fd5a90 100644
--- a/src/src/tls-openssl.c
+++ b/src/src/tls-openssl.c
@@ -779,11 +779,6 @@ a TLS session.
 
 Arguments:
   require_ciphers   allowed ciphers
-  ------------------------------------------------------
-  require_mac      list of allowed MACs                 ) Not used
-  require_kx       list of allowed key_exchange methods )   for
-  require_proto    list of allowed protocols            ) OpenSSL
-  ------------------------------------------------------
 
 Returns:            OK on success
                     DEFER for errors before the start of the negotiation
@@ -792,8 +787,7 @@ Returns:            OK on success
 */
 
 int
-tls_server_start(uschar *require_ciphers, uschar *require_mac,
-  uschar *require_kx, uschar *require_proto)
+tls_server_start(const uschar *require_ciphers)
 {
 int rc;
 uschar *expciphers;
@@ -819,8 +813,9 @@ if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
   return FAIL;
 
 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
-are separated by underscores. So that I can use either form in my tests, and
-also for general convenience, we turn underscores into hyphens here. */
+were historically separated by underscores. So that I can use either form in my
+tests, and also for general convenience, we turn underscores into hyphens here.
+*/
 
 if (expciphers != NULL)
   {
@@ -954,11 +949,6 @@ Argument:
   verify_certs     file for certificate verify
   crl              file containing CRL
   require_ciphers  list of allowed ciphers
-  ------------------------------------------------------
-  require_mac      list of allowed MACs                 ) Not used
-  require_kx       list of allowed key_exchange methods )   for
-  require_proto    list of allowed protocols            ) OpenSSL
-  ------------------------------------------------------
   timeout          startup timeout
 
 Returns:           OK on success
@@ -970,8 +960,7 @@ int
 tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam,
   uschar *certificate, uschar *privatekey, uschar *sni,
   uschar *verify_certs, uschar *crl,
-  uschar *require_ciphers, uschar *require_mac, uschar *require_kx,
-  uschar *require_proto, int timeout)
+  uschar *require_ciphers, int timeout)
 {
 static uschar txt[256];
 uschar *expciphers;
@@ -1292,7 +1281,7 @@ fprintf(f, "Library version: OpenSSL: Compile: %s\n"
 
 
 /*************************************************
-*        Pseudo-random number generation         *
+*            Random number generation            *
 *************************************************/
 
 /* Pseudo-random number generation.  The result is not expected to be
@@ -1307,7 +1296,7 @@ Returns     a random number in range [0, max-1]
 */
 
 int
-pseudo_random_number(int max)
+vaguely_random_number(int max)
 {
 unsigned int r;
 int i, needed_len;
@@ -1343,7 +1332,14 @@ if (i < needed_len)
   needed_len = i;
 
 /* We do not care if crypto-strong */
-(void) RAND_pseudo_bytes(smallbuf, needed_len);
+i = RAND_pseudo_bytes(smallbuf, needed_len);
+if (i < 0)
+  {
+  DEBUG(D_all)
+    debug_printf("OpenSSL RAND_pseudo_bytes() not supported by RAND method, using fallback.\n");
+  return vaguely_random_number_fallback(max);
+  }
+
 r = 0;
 for (p = smallbuf; needed_len; --needed_len, ++p)
   {
diff --git a/src/src/tls.c b/src/src/tls.c
index d975a2c89..f0eba37f8 100644
--- a/src/src/tls.c
+++ b/src/src/tls.c
@@ -34,7 +34,7 @@ functions and the common functions below. */
 
 
 static uschar *ssl_xfer_buffer = NULL;
-static int ssl_xfer_buffer_size = 4096;
+static const int ssl_xfer_buffer_size = 4096;
 static int ssl_xfer_buffer_lwm = 0;
 static int ssl_xfer_buffer_hwm = 0;
 static int ssl_xfer_eof = 0;
@@ -59,11 +59,11 @@ Returns:    TRUE if OK; result may still be NULL after forced failure
 */
 
 static BOOL
-expand_check(uschar *s, uschar *name, uschar **result)
+expand_check(const uschar *s, const uschar *name, uschar **result)
 {
 if (s == NULL) *result = NULL; else
   {
-  *result = expand_string(s);
+  *result = expand_string(US s); /* need to clean up const some more */
   if (*result == NULL && !expand_string_forcedfail)
     {
     log_write(0, LOG_MAIN|LOG_PANIC, "expansion of %s failed: %s", name,
diff --git a/src/src/transports/smtp.c b/src/src/transports/smtp.c
index 6ec94d5da..b01322662 100644
--- a/src/src/transports/smtp.c
+++ b/src/src/transports/smtp.c
@@ -62,6 +62,9 @@ optionlist smtp_transport_options[] = {
   { "gethostbyname",        opt_bool,
       (void *)offsetof(smtp_transport_options_block, gethostbyname) },
 #ifdef SUPPORT_TLS
+  /* These are no longer honoured, as of Exim 4.78; for now, we silently
+  ignore; a later release will warn, and a later-still release will remove
+  these options, so that using them becomes an error. */
   { "gnutls_require_kx",    opt_stringptr,
       (void *)offsetof(smtp_transport_options_block, gnutls_require_kx) },
   { "gnutls_require_mac",   opt_stringptr,
@@ -1133,9 +1136,6 @@ if (tls_offered && !suppress_tls &&
       ob->tls_verify_certificates,
       ob->tls_crl,
       ob->tls_require_ciphers,
-      ob->gnutls_require_mac,
-      ob->gnutls_require_kx,
-      ob->gnutls_require_proto,
       ob->command_timeout);
 
     /* TLS negotiation failed; give an error. From outside, this function may
author	Phil Pennock <pdp@exim.org>	2012-05-16 12:15:26 -0400
committer	Phil Pennock <pdp@exim.org>	2012-05-16 12:15:26 -0400
commit	17c761988f30054827a9951761d93ffeeaad0cb7 (patch)
tree	10d8b048f0c7059c28a2ad5e4257a19e46d47267 /src
parent	f675bf30a2ce6242cfc7c3e3997ec5d68a1fca7a (diff)