Revert "GnuTLS: lose DH-param setup, for recent library versions where no longer needed". Bug 2822

It seems the documentation lies and the params really are needed.

This reverts commits 041bf37266, 49132a3bb5c6

2 files changed, 15 insertions, 26 deletions

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index dcda2ff79..a8cd63b19 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -18429,12 +18429,7 @@ larger prime than requested.
 The value of this option is expanded and indicates the source of DH parameters
 to be used by Exim.
 
-This option is ignored for GnuTLS version 3.6.0 and later.
-The library manages parameter negotiation internally.
-
-&*Note: The Exim Maintainers strongly recommend,
-for other TLS library versions,
-using a filename with site-generated
+&*Note: The Exim Maintainers strongly recommend using a filename with site-generated
 local DH parameters*&, which has been supported across all versions of Exim.  The
 other specific constants available are a fallback so that even when
 "unconfigured", Exim can offer Perfect Forward Secrecy in older ciphersuites in TLS.
diff --git a/src/src/tls-gnu.c b/src/src/tls-gnu.c
index aea1bd8b2..7b67bb793 100644
--- a/src/src/tls-gnu.c
+++ b/src/src/tls-gnu.c
@@ -89,9 +89,6 @@ require current GnuTLS, then we'll drop support for the ancient libraries).
 #if GNUTLS_VERSION_NUMBER >= 0x030506 && !defined(DISABLE_OCSP)
 # define SUPPORT_SRV_OCSP_STACK
 #endif
-#if GNUTLS_VERSION_NUMBER >= 0x030600
-# define GNUTLS_AUTO_DHPARAMS
-#endif
 #if GNUTLS_VERSION_NUMBER >= 0x030603
 # define EXIM_HAVE_TLS1_3
 # define SUPPORT_GNUTLS_EXT_RAW_PARSE
@@ -265,13 +262,11 @@ static exim_gnutls_state_st state_server = {
   .fd_out =		-1,
 };
 
-#ifndef GNUTLS_AUTO_DHPARAMS
 /* 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 gnutls_dh_params_t dh_server_params = NULL;
-#endif
 
 static int ssl_session_timeout = 7200;	/* Two hours */
 
@@ -688,7 +683,6 @@ if (!state->host)
 
 
 
-#ifndef GNUTLS_AUTO_DHPARAMS
 /*************************************************
 *            Setup up DH parameters              *
 *************************************************/
@@ -711,7 +705,7 @@ init_server_dh(uschar ** errstr)
 {
 int fd, rc;
 unsigned int dh_bits;
-gnutls_datum_t m = {.data = NULL, .size = 0};
+gnutls_datum_t m;
 uschar filename_buf[PATH_MAX];
 uschar *filename = NULL;
 size_t sz;
@@ -724,6 +718,9 @@ DEBUG(D_tls) debug_printf("Initialising GnuTLS server params\n");
 if ((rc = gnutls_dh_params_init(&dh_server_params)))
   return tls_error_gnu(NULL, US"gnutls_dh_params_init", rc, errstr);
 
+m.data = NULL;
+m.size = 0;
+
 if (!expand_check(tls_dhparam, US"tls_dhparam", &exp_tls_dhparam, errstr))
   return DEFER;
 
@@ -873,12 +870,14 @@ if (rc < 0)
     return tls_error_sys(US"Unable to open temp file", errno, NULL, errstr);
   (void)exim_chown(temp_fn, exim_uid, exim_gid);   /* Probably not necessary */
 
-  /* GnuTLS overshoots!  If we ask for 2236, we might get 2237 or more.  But
-  there's no way to ask GnuTLS how many bits there really are.  We can ask
-  how many bits were used in a TLS session, but that's it!  The prime itself
-  is hidden behind too much abstraction.  So we ask for less, and proceed on
-  a wing and a prayer.  First attempt, subtracted 3 for 2233 and got 2240.  */
-
+  /* GnuTLS overshoots!
+   * If we ask for 2236, we might get 2237 or more.
+   * But there's no way to ask GnuTLS how many bits there really are.
+   * We can ask how many bits were used in a TLS session, but that's it!
+   * The prime itself is hidden behind too much abstraction.
+   * So we ask for less, and proceed on a wing and a prayer.
+   * First attempt, subtracted 3 for 2233 and got 2240.
+   */
   if (dh_bits >= EXIM_CLIENT_DH_MIN_BITS + 10)
     {
     dh_bits_gen = dh_bits - 10;
@@ -941,7 +940,6 @@ if (rc < 0)
 DEBUG(D_tls) debug_printf("initialized server D-H parameters\n");
 return OK;
 }
-#endif
 
 
 
@@ -1952,7 +1950,6 @@ tls_set_remaining_x509(exim_gnutls_state_st *state, uschar ** errstr)
 int rc;
 const host_item *host = state->host;  /* macro should be reconsidered? */
 
-#ifndef GNUTLS_AUTO_DHPARAMS
 /* 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. */
@@ -1962,13 +1959,10 @@ if (!state->host)
   if (!dh_server_params)
     if ((rc = init_server_dh(errstr)) != OK) return rc;
 
-  /* Unnecessary & discouraged with 3.6.0 or later */
+  /* Unnecessary & discouraged with 3.6.0 or later, according to docs.  But without it,
+  no DHE- ciphers are advertised. */
   gnutls_certificate_set_dh_params(state->lib_state.x509_cred, dh_server_params);
   }
-#else
-DEBUG(D_tls) if (tls_dhparam)
-  debug_printf("Ignoring tls_dhparam (recent version GnuTLS)\n");
-#endif
 
 /* Link the credentials to the session. */