GnuTLS: simplify cert hostname checking

3 files changed, 36 insertions, 19 deletions

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index a93b39474..8fde6397c 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -27773,7 +27773,7 @@ session with a client, you must set either &%tls_verify_hosts%& or
 apply to all TLS connections. For any host that matches one of these options,
 Exim requests a certificate as part of the setup of the TLS session. The
 contents of the certificate are verified by comparing it with a list of
-expected certificates.
+expected trust-anchors or certificates.
 These may be the system default set (depending on library version),
 an explicit file or,
 depending on library version, a directory, identified by
@@ -27790,6 +27790,9 @@ openssl x509 -hash -noout -in /cert/file
 .endd
 where &_/cert/file_& contains a single certificate.
 
+There is no checking of names of the client against the certificate
+Subject Name or Subject Alternate Names.
+
 The difference between &%tls_verify_hosts%& and &%tls_try_verify_hosts%& is
 what happens if the client does not supply a certificate, or if the certificate
 does not match any of the certificates in the collection named by
@@ -27951,6 +27954,11 @@ The &%tls_verify_hosts%& and &%tls_try_verify_hosts%& options restrict
 certificate verification to the listed servers.  Verification either must
 or need not succeed respectively.
 
+The &%tls_verify_cert_hostnames%& option lists hosts for which additional
+checks are made: that the host name (the one in the DNS A record)
+is valid for the certificate.
+The option defaults to always checking.
+
 The &(smtp)& transport has two OCSP-related options:
 &%hosts_require_ocsp%&; a host-list for which a Certificate Status
 is requested and required for the connection to proceed.  The default
@@ -28256,7 +28264,7 @@ this is appropriate for a single system, using a self-signed certificate.
 DANE-TA usage is effectively declaring a specific CA to be used; this might be a private CA or a public,
 well-known one.
 A private CA at simplest is just a self-signed certificate (with certain
-attributes) which is used to sign cerver certificates, but running one securely
+attributes) which is used to sign server certificates, but running one securely
 does require careful arrangement.
 With DANE-TA, as implemented in Exim and commonly in other MTAs,
 the server TLS handshake must transmit the entire certificate chain from CA to server-certificate.
diff --git a/src/src/tls-gnu.c b/src/src/tls-gnu.c
index 9fcb50dfe..ff8064bab 100644
--- a/src/src/tls-gnu.c
+++ b/src/src/tls-gnu.c
@@ -124,7 +124,7 @@ typedef struct exim_gnutls_state {
   BOOL			peer_dane_verified;
   BOOL			trigger_sni_changes;
   BOOL			have_set_peerdn;
-  const struct host_item *host;
+  const struct host_item *host;		/* NULL if server */
   gnutls_x509_crt_t	peercert;
   uschar		*peerdn;
   uschar		*ciphersuite;
@@ -1757,23 +1757,23 @@ if (rc < 0 || verify & (GNUTLS_CERT_INVALID|GNUTLS_CERT_REVOKED))
 
 else
   {
-  if (state->exp_tls_verify_cert_hostnames)
+  /* Client side, check the server's certificate name versus the name on the
+  A-record for the connection we made.  What to do for server side - what name
+  to use for client?  We document that there is no such checking for server
+  side. */
+
+  if (  state->exp_tls_verify_cert_hostnames
+     && !gnutls_x509_crt_check_hostname(state->tlsp->peercert,
+		CS state->exp_tls_verify_cert_hostnames)
+     )
     {
-    int sep = 0;
-    const uschar * list = state->exp_tls_verify_cert_hostnames;
-    uschar * name;
-    while ((name = string_nextinlist(&list, &sep, NULL, 0)))
-      if (gnutls_x509_crt_check_hostname(state->tlsp->peercert, CS name))
-	break;
-    if (!name)
-      {
-      DEBUG(D_tls)
-	debug_printf("TLS certificate verification failed: cert name mismatch\n");
-      if (state->verify_requirement >= VERIFY_REQUIRED)
-	goto badcert;
-      return TRUE;
-      }
+    DEBUG(D_tls)
+      debug_printf("TLS certificate verification failed: cert name mismatch\n");
+    if (state->verify_requirement >= VERIFY_REQUIRED)
+      goto badcert;
+    return TRUE;
     }
+
   state->peer_cert_verified = TRUE;
   DEBUG(D_tls) debug_printf("TLS certificate verified: peerdn=\"%s\"\n",
       state->peerdn ? state->peerdn : US"<unset>");
@@ -2591,6 +2591,7 @@ else if (inbytes == 0)
 
 else if (inbytes < 0)
   {
+debug_printf("%s: err from gnutls_record_recv(\n", __FUNCTION__);
   record_io_error(state, (int) inbytes, US"recv", NULL);
   state->xfer_error = TRUE;
   return FALSE;
@@ -2718,7 +2719,11 @@ if (inbytes == 0)
   {
   DEBUG(D_tls) debug_printf("Got TLS_EOF\n");
   }
-else record_io_error(state, (int)inbytes, US"recv", NULL);
+else
+{
+debug_printf("%s: err from gnutls_record_recv(\n", __FUNCTION__);
+record_io_error(state, (int)inbytes, US"recv", NULL);
+}
 
 return -1;
 }
@@ -2765,6 +2770,7 @@ while (left > 0)
   DEBUG(D_tls) debug_printf("outbytes=" SSIZE_T_FMT "\n", outbytes);
   if (outbytes < 0)
     {
+debug_printf("%s: err from gnutls_record_send(\n", __FUNCTION__);
     record_io_error(state, outbytes, US"send", NULL);
     return -1;
     }
diff --git a/test/confs/2001 b/test/confs/2001
index 9ab4cc384..715da4bf6 100644
--- a/test/confs/2001
+++ b/test/confs/2001
@@ -27,6 +27,9 @@ tls_verify_hosts = *
 tls_verify_certificates = ${if eq {SERVER}{server}{DIR/aux-fixed/cert2}fail}
 
 
+# so we can decode in wireshark
+tls_require_ciphers = NORMAL:-KX-ALL:+RSA
+
 # ----- Routers -----
 
 begin routers