X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/e7a0bf3f71cd20b710a24f6cd9e0ab685d67d75f..c6a290f4d8df3734b3cdc2232b4334ff8386c1da:/src/src/tls-openssl.c

diff --git a/src/src/tls-openssl.c b/src/src/tls-openssl.c
index 906c98cef..4bc92bd05 100644
--- a/src/src/tls-openssl.c
+++ b/src/src/tls-openssl.c
@@ -3,7 +3,7 @@
 *************************************************/
 
 /* Copyright (c) University of Cambridge 1995 - 2019 */
-/* Copyright (c) The Exim Maintainers 2020 */
+/* Copyright (c) The Exim Maintainers 2020 - 2021 */
 /* See the file NOTICE for conditions of use and distribution. */
 
 /* Portions Copyright (c) The OpenSSL Project 1999 */
@@ -80,6 +80,7 @@ change this guard and punt the issue for a while longer. */
 #  ifndef DISABLE_OCSP
 #   define EXIM_HAVE_OCSP
 #  endif
+#  define EXIM_HAVE_ALPN /* fail ret from hshake-cb is ignored by LibreSSL */
 # else
 #  define EXIM_NEED_OPENSSL_INIT
 # endif
@@ -89,6 +90,10 @@ change this guard and punt the issue for a while longer. */
 # endif
 #endif
 
+#if LIBRESSL_VERSION_NUMBER >= 0x3040000fL
+# define EXIM_HAVE_OPENSSL_CIPHER_GET_ID
+#endif
+
 #if !defined(LIBRESSL_VERSION_NUMBER) \
     || LIBRESSL_VERSION_NUMBER >= 0x20010000L
 # if !defined(OPENSSL_NO_ECDH)
@@ -227,12 +232,16 @@ static exim_openssl_option exim_openssl_options[] = {
   { US"no_tlsv1", SSL_OP_NO_TLSv1 },
 #endif
 #ifdef SSL_OP_NO_TLSv1_1
-#if SSL_OP_NO_TLSv1_1 == 0x00000400L
+# if OPENSSL_VERSION_NUMBER < 0x30000000L
+#  if SSL_OP_NO_TLSv1_1 == 0x00000400L
   /* Error in chosen value in 1.0.1a; see first item in CHANGES for 1.0.1b */
-#warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
-#else
+#   warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
+#   define NO_SSL_OP_NO_TLSv1_1
+#  endif
+# endif
+# ifndef NO_SSL_OP_NO_TLSv1_1
   { US"no_tlsv1_1", SSL_OP_NO_TLSv1_1 },
-#endif
+# endif
 #endif
 #ifdef SSL_OP_NO_TLSv1_2
   { US"no_tlsv1_2", SSL_OP_NO_TLSv1_2 },
@@ -306,6 +315,9 @@ builtin_macro_create(US"_TLS_BAD_MULTICERT_IN_OURCERT");
 builtin_macro_create(US"_HAVE_TLS_OCSP");
 builtin_macro_create(US"_HAVE_TLS_OCSP_LIST");
 # endif
+# ifdef EXIM_HAVE_ALPN
+builtin_macro_create(US"_HAVE_TLS_ALPN");
+# endif
 }
 #else
 
@@ -358,6 +370,9 @@ typedef struct {
 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 static SSL_CTX *server_sni = NULL;
 #endif
+#ifdef EXIM_HAVE_ALPN
+static BOOL server_seen_alpn = FALSE;
+#endif
 
 static char ssl_errstring[256];
 
@@ -418,9 +433,6 @@ setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host,
     uschar ** errstr );
 
 /* Callbacks */
-#ifdef EXIM_HAVE_OPENSSL_TLSEXT
-static int tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg);
-#endif
 #ifndef DISABLE_OCSP
 static int tls_server_stapling_cb(SSL *s, void *arg);
 #endif
@@ -537,23 +549,27 @@ EVP_add_digest(EVP_sha256());
 *************************************************/
 
 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
+Server only.
 
 Arguments:
   sctx      The current SSL CTX (inbound or outbound)
   dhparam   DH parameter file or fixed parameter identity string
-  host      connected host, if client; NULL if server
   errstr    error string pointer
 
 Returns:    TRUE if OK (nothing to set up, or setup worked)
 */
 
 static BOOL
-init_dh(SSL_CTX *sctx, uschar *dhparam, const host_item *host, uschar ** errstr)
+init_dh(SSL_CTX * sctx, uschar * dhparam, uschar ** errstr)
 {
-BIO *bio;
-DH *dh;
-uschar *dhexpanded;
-const char *pem;
+BIO * bio;
+#if OPENSSL_VERSION_NUMBER < 0x30000000L
+DH * dh;
+#else
+EVP_PKEY * pkey;
+#endif
+uschar * dhexpanded;
+const char * pem;
 int dh_bitsize;
 
 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded, errstr))
@@ -566,7 +582,7 @@ else if (dhexpanded[0] == '/')
   if (!(bio = BIO_new_file(CS dhexpanded, "r")))
     {
     tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
-          host, US strerror(errno), errstr);
+          NULL, US strerror(errno), errstr);
     return FALSE;
     }
   }
@@ -581,53 +597,80 @@ else
   if (!(pem = std_dh_prime_named(dhexpanded)))
     {
     tls_error(string_sprintf("Unknown standard DH prime \"%s\"", dhexpanded),
-        host, US strerror(errno), errstr);
+        NULL, US strerror(errno), errstr);
     return FALSE;
     }
   bio = BIO_new_mem_buf(CS pem, -1);
   }
 
-if (!(dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)))
+if (!(
+#if OPENSSL_VERSION_NUMBER < 0x30000000L
+      dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)
+#else
+      pkey = PEM_read_bio_Parameters_ex(bio, NULL, NULL, NULL)
+#endif
+   ) )
   {
   BIO_free(bio);
   tls_error(string_sprintf("Could not read tls_dhparams \"%s\"", dhexpanded),
-      host, NULL, errstr);
+      NULL, NULL, errstr);
   return FALSE;
   }
 
 /* note: our default limit of 2236 is not a multiple of 8; the limit comes from
- * an NSS limit, and the GnuTLS APIs handle bit-sizes fine, so we went with
- * 2236.  But older OpenSSL can only report in bytes (octets), not bits.
- * If someone wants to dance at the edge, then they can raise the limit or use
- * current libraries. */
-#ifdef EXIM_HAVE_OPENSSL_DH_BITS
+an NSS limit, and the GnuTLS APIs handle bit-sizes fine, so we went with 2236.
+But older OpenSSL can only report in bytes (octets), not bits.  If someone wants
+to dance at the edge, then they can raise the limit or use current libraries. */
+
+#if OPENSSL_VERSION_NUMBER < 0x30000000L
+# ifdef EXIM_HAVE_OPENSSL_DH_BITS
 /* Added in commit 26c79d5641d; `git describe --contains` says OpenSSL_1_1_0-pre1~1022
- * This predates OpenSSL_1_1_0 (before a, b, ...) so is in all 1.1.0 */
+This predates OpenSSL_1_1_0 (before a, b, ...) so is in all 1.1.0 */
 dh_bitsize = DH_bits(dh);
-#else
+# else
 dh_bitsize = 8 * DH_size(dh);
+# endif
+#else	/* 3.0.0 + */
+dh_bitsize = EVP_PKEY_get_bits(pkey);
 #endif
 
-/* Even if it is larger, we silently return success rather than cause things
- * to fail out, so that a too-large DH will not knock out all TLS; it's a
- * debatable choice. */
-if (dh_bitsize > tls_dh_max_bits)
+/* Even if it is larger, we silently return success rather than cause things to
+fail out, so that a too-large DH will not knock out all TLS; it's a debatable
+choice.  Likewise for a failing attempt to set one. */
+
+if (dh_bitsize <= tls_dh_max_bits)
   {
-  DEBUG(D_tls)
-    debug_printf("dhparams file %d bits, is > tls_dh_max_bits limit of %d\n",
-        dh_bitsize, tls_dh_max_bits);
+  if (
+#if OPENSSL_VERSION_NUMBER < 0x30000000L
+      SSL_CTX_set_tmp_dh(sctx, dh)
+#else
+      SSL_CTX_set0_tmp_dh_pkey(sctx, pkey)
+#endif
+      == 0)
+    {
+    ERR_error_string_n(ERR_get_error(), ssl_errstring, sizeof(ssl_errstring));
+    log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (D-H param setting '%s'): %s",
+	dhexpanded ? dhexpanded : US"default", ssl_errstring);
+#if OPENSSL_VERSION_NUMBER >= 0x30000000L
+    /* EVP_PKEY_free(pkey);  crashes */
+#endif
+    }
+  else
+    DEBUG(D_tls)
+      debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
+	dhexpanded ? dhexpanded : US"default", dh_bitsize);
   }
 else
-  {
-  SSL_CTX_set_tmp_dh(sctx, dh);
   DEBUG(D_tls)
-    debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
-      dhexpanded ? dhexpanded : US"default", dh_bitsize);
-  }
+    debug_printf("dhparams '%s' %d bits, is > tls_dh_max_bits limit of %d\n",
+	dhexpanded ? dhexpanded : US"default", dh_bitsize, tls_dh_max_bits);
 
+#if OPENSSL_VERSION_NUMBER < 0x30000000L
 DH_free(dh);
-BIO_free(bio);
+#endif
+/* The EVP_PKEY ownership stays with the ctx; do not free it */
 
+BIO_free(bio);
 return TRUE;
 }
 
@@ -638,7 +681,7 @@ return TRUE;
 *               Initialize for ECDH              *
 *************************************************/
 
-/* Load parameters for ECDH encryption.
+/* Load parameters for ECDH encryption.  Server only.
 
 For now, we stick to NIST P-256 because: it's simple and easy to configure;
 it avoids any patent issues that might bite redistributors; despite events in
@@ -656,27 +699,22 @@ Patches welcome.
 
 Arguments:
   sctx      The current SSL CTX (inbound or outbound)
-  host      connected host, if client; NULL if server
   errstr    error string pointer
 
 Returns:    TRUE if OK (nothing to set up, or setup worked)
 */
 
 static BOOL
-init_ecdh(SSL_CTX * sctx, host_item * host, uschar ** errstr)
+init_ecdh(SSL_CTX * sctx, uschar ** errstr)
 {
 #ifdef OPENSSL_NO_ECDH
 return TRUE;
 #else
 
-EC_KEY * ecdh;
 uschar * exp_curve;
 int nid;
 BOOL rv;
 
-if (host)	/* No ECDH setup for clients, only for servers */
-  return TRUE;
-
 # ifndef EXIM_HAVE_ECDH
 DEBUG(D_tls)
   debug_printf("No OpenSSL API to define ECDH parameters, skipping\n");
@@ -723,25 +761,38 @@ if (  (nid = OBJ_sn2nid       (CCS exp_curve)) == NID_undef
    )
   {
   tls_error(string_sprintf("Unknown curve name tls_eccurve '%s'", exp_curve),
-    host, NULL, errstr);
+    NULL, NULL, errstr);
   return FALSE;
   }
 
-if (!(ecdh = EC_KEY_new_by_curve_name(nid)))
-  {
-  tls_error(US"Unable to create ec curve", host, NULL, errstr);
-  return FALSE;
-  }
+# if OPENSSL_VERSION_NUMBER < 0x30000000L
+ {
+  EC_KEY * ecdh;
+  if (!(ecdh = EC_KEY_new_by_curve_name(nid)))
+    {
+    tls_error(US"Unable to create ec curve", NULL, NULL, errstr);
+    return FALSE;
+    }
 
-/* The "tmp" in the name here refers to setting a temporary key
-not to the stability of the interface. */
+  /* The "tmp" in the name here refers to setting a temporary key
+  not to the stability of the interface. */
 
-if ((rv = SSL_CTX_set_tmp_ecdh(sctx, ecdh) == 0))
-  tls_error(string_sprintf("Error enabling '%s' curve", exp_curve), host, NULL, errstr);
+  if ((rv = SSL_CTX_set_tmp_ecdh(sctx, ecdh) == 0))
+    tls_error(string_sprintf("Error enabling '%s' curve", exp_curve), NULL, NULL, errstr);
+  else
+    DEBUG(D_tls) debug_printf("ECDH: enabled '%s' curve\n", exp_curve);
+  EC_KEY_free(ecdh);
+ }
+
+#else	/* v 3.0.0 + */
+
+if ((rv = SSL_CTX_set1_groups(sctx, &nid, 1)) == 0)
+  tls_error(string_sprintf("Error enabling '%s' group", exp_curve), NULL, NULL, errstr);
 else
-  DEBUG(D_tls) debug_printf("ECDH: enabled '%s' curve\n", exp_curve);
+  DEBUG(D_tls) debug_printf("ECDH: enabled '%s' group\n", exp_curve);
+
+#endif
 
-EC_KEY_free(ecdh);
 return !rv;
 
 # endif	/*EXIM_HAVE_ECDH*/
@@ -1650,15 +1701,19 @@ state_server.lib_state.lib_ctx = ctx;
 if (opt_unset_or_noexpand(tls_dhparam))
   {
   DEBUG(D_tls) debug_printf("TLS: preloading DH params for server\n");
-  if (init_dh(ctx, tls_dhparam, NULL, &dummy_errstr))
+  if (init_dh(ctx, tls_dhparam, &dummy_errstr))
     state_server.lib_state.dh = TRUE;
   }
+else
+  DEBUG(D_tls) debug_printf("TLS: not preloading DH params for server\n");
 if (opt_unset_or_noexpand(tls_eccurve))
   {
   DEBUG(D_tls) debug_printf("TLS: preloading ECDH curve for server\n");
-  if (init_ecdh(ctx, NULL, &dummy_errstr))
+  if (init_ecdh(ctx, &dummy_errstr))
     state_server.lib_state.ecdh = TRUE;
   }
+else
+  DEBUG(D_tls) debug_printf("TLS: not preloading ECDH curve for server\n");
 
 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
 /* If we can, preload the server-side cert, key and ocsp */
@@ -1770,19 +1825,6 @@ ob->tls_preload.lib_ctx = ctx;
 
 tpt_dummy_state.lib_state = ob->tls_preload;
 
-if (opt_unset_or_noexpand(tls_dhparam))
-  {
-  DEBUG(D_tls) debug_printf("TLS: preloading DH params for transport '%s'\n", t->name);
-  if (init_dh(ctx, tls_dhparam, NULL, &dummy_errstr))
-    ob->tls_preload.dh = TRUE;
-  }
-if (opt_unset_or_noexpand(tls_eccurve))
-  {
-  DEBUG(D_tls) debug_printf("TLS: preloading ECDH curve for transport '%s'\n", t->name);
-  if (init_ecdh(ctx, NULL, &dummy_errstr))
-    ob->tls_preload.ecdh = TRUE;
-  }
-
 #if defined(EXIM_HAVE_INOTIFY) || defined(EXIM_HAVE_KEVENT)
 if (  opt_set_and_noexpand(ob->tls_certificate)
    && opt_unset_or_noexpand(ob->tls_privatekey))
@@ -2092,8 +2134,8 @@ already exists.  Might even need this selfsame callback, for reneg? */
   SSL_CTX_set_tlsext_servername_arg(server_sni, state);
   }
 
-if (  !init_dh(server_sni, state->dhparam, NULL, &dummy_errstr)
-   || !init_ecdh(server_sni, NULL, &dummy_errstr)
+if (  !init_dh(server_sni, state->dhparam, &dummy_errstr)
+   || !init_ecdh(server_sni, &dummy_errstr)
    )
   goto bad;
 
@@ -2137,6 +2179,61 @@ bad: return SSL_TLSEXT_ERR_ALERT_FATAL;
 
 
 
+#ifdef EXIM_HAVE_ALPN
+/*************************************************
+*        Callback to handle ALPN                 *
+*************************************************/
+
+/* Called on server if tls_alpn nonblank after expansion,
+when client offers ALPN, after the SNI callback.
+If set and not matching the list then we dump the connection */
+
+static int
+tls_server_alpn_cb(SSL *ssl, const uschar ** out, uschar * outlen,
+  const uschar * in, unsigned int inlen, void * arg)
+{
+server_seen_alpn = TRUE;
+DEBUG(D_tls)
+  {
+  debug_printf("Received TLS ALPN offer:");
+  for (int pos = 0, siz; pos < inlen; pos += siz+1)
+    {
+    siz = in[pos];
+    if (pos + 1 + siz > inlen) siz = inlen - pos - 1;
+    debug_printf(" '%.*s'", siz, in + pos + 1);
+    }
+  debug_printf(".  Our list: '%s'\n", tls_alpn);
+  }
+
+/* Look for an acceptable ALPN */
+
+if (  inlen > 1		/* at least one name */
+   && in[0]+1 == inlen	/* filling the vector, so exactly one name */
+   )
+  {
+  const uschar * list = tls_alpn;
+  int sep = 0;
+  for (uschar * name; name = string_nextinlist(&list, &sep, NULL, 0); )
+    if (Ustrncmp(in+1, name, in[0]) == 0)
+      {
+      *out = in+1;			/* we checked for exactly one, so can just point to it */
+      *outlen = inlen;
+      return SSL_TLSEXT_ERR_OK;		/* use ALPN */
+      }
+  }
+
+/* More than one name from clilent, or name did not match our list. */
+
+/* This will be fatal to the TLS conn; would be nice to kill TCP also.
+Maybe as an option in future; for now leave control to the config (must-tls). */
+
+DEBUG(D_tls) debug_printf("TLS ALPN rejected\n");
+return SSL_TLSEXT_ERR_ALERT_FATAL;
+}
+#endif	/* EXIM_HAVE_ALPN */
+
+
+
 #ifndef DISABLE_OCSP
 
 /*************************************************
@@ -2172,9 +2269,6 @@ if (!olist)
   const X509 * cert_sent = SSL_get_certificate(s);
   const ASN1_INTEGER * cert_serial = X509_get0_serialNumber(cert_sent);
   const BIGNUM * cert_bn = ASN1_INTEGER_to_BN(cert_serial, NULL);
-  const X509_NAME * cert_issuer = X509_get_issuer_name(cert_sent);
-  uschar * chash;
-  uint chash_len;
 
   for (; olist; olist = olist->next)
     {
@@ -2546,15 +2640,18 @@ will never be used because we use a new context every time. */
 /* Initialize with DH parameters if supplied */
 /* Initialize ECDH temp key parameter selection */
 
-if (state->lib_state.dh)
-  { DEBUG(D_tls) debug_printf("TLS: DH params were preloaded\n"); }
-else
-  if (!init_dh(ctx, state->dhparam, host, errstr)) return DEFER;
+if (!host)
+  {
+  if (state->lib_state.dh)
+    { DEBUG(D_tls) debug_printf("TLS: DH params were preloaded\n"); }
+  else
+    if (!init_dh(ctx, state->dhparam, errstr)) return DEFER;
 
-if (state->lib_state.ecdh)
-  { DEBUG(D_tls) debug_printf("TLS: ECDH curve was preloaded\n"); }
-else
-  if (!init_ecdh(ctx, host, errstr)) return DEFER;
+  if (state->lib_state.ecdh)
+    { DEBUG(D_tls) debug_printf("TLS: ECDH curve was preloaded\n"); }
+  else
+    if (!init_ecdh(ctx, errstr)) return DEFER;
+  }
 
 /* Set up certificate and key (and perhaps OCSP info) */
 
@@ -2604,6 +2701,21 @@ if (!host)		/* server */
   tls_certificate */
   SSL_CTX_set_tlsext_servername_callback(ctx, tls_servername_cb);
   SSL_CTX_set_tlsext_servername_arg(ctx, state);
+
+# ifdef EXIM_HAVE_ALPN
+  if (tls_alpn && *tls_alpn)
+    {
+    uschar * exp_alpn;
+    if (  expand_check(tls_alpn, US"tls_alpn", &exp_alpn, errstr)
+       && *exp_alpn && !isblank(*exp_alpn))
+      {
+      tls_alpn = exp_alpn;	/* subprocess so ok to overwrite */
+      SSL_CTX_set_alpn_select_cb(ctx, tls_server_alpn_cb, state);
+      }
+    else
+      tls_alpn = NULL;
+    }
+# endif
   }
 # ifndef DISABLE_OCSP
 else			/* client */
@@ -2760,18 +2872,22 @@ if (tlsp->peercert)
 /* Load certs from file, return TRUE on success */
 
 static BOOL
-chain_from_pem_file(const uschar * file, STACK_OF(X509) * verify_stack)
+chain_from_pem_file(const uschar * file, STACK_OF(X509) ** vp)
 {
 BIO * bp;
-X509 * x;
+STACK_OF(X509) * verify_stack = *vp;
 
-while (sk_X509_num(verify_stack) > 0)
-  X509_free(sk_X509_pop(verify_stack));
+if (verify_stack)
+  while (sk_X509_num(verify_stack) > 0)
+    X509_free(sk_X509_pop(verify_stack));
+else
+  verify_stack = sk_X509_new_null();
 
 if (!(bp = BIO_new_file(CS file, "r"))) return FALSE;
-while ((x = PEM_read_bio_X509(bp, NULL, 0, NULL)))
+for (X509 * x; x = PEM_read_bio_X509(bp, NULL, 0, NULL); )
   sk_X509_push(verify_stack, x);
 BIO_free(bp);
+*vp = verify_stack;
 return TRUE;
 }
 #endif
@@ -2826,6 +2942,13 @@ if (expcerts && *expcerts)
 	{ file = NULL; dir = expcerts; }
       else
 	{
+	STACK_OF(X509) * verify_stack =
+#ifndef DISABLE_OCSP
+	  !host ? state_server.verify_stack :
+#endif
+	  NULL;
+	STACK_OF(X509) ** vp = &verify_stack;
+
 	file = expcerts; dir = NULL;
 #ifndef DISABLE_OCSP
 	/* In the server if we will be offering an OCSP proof, load chain from
@@ -2834,11 +2957,10 @@ if (expcerts && *expcerts)
 /*XXX Glitch!   The file here is tls_verify_certs: the chain for verifying the client cert.
 This is inconsistent with the need to verify the OCSP proof of the server cert.
 */
-
 	if (  !host
 	   && statbuf.st_size > 0
 	   && state_server.u_ocsp.server.file
-	   && !chain_from_pem_file(file, state_server.verify_stack)
+	   && !chain_from_pem_file(file, vp)
 	   )
 	  {
 	  log_write(0, LOG_MAIN|LOG_PANIC,
@@ -3025,7 +3147,7 @@ else if (verify_check_host(&tls_try_verify_hosts) == OK)
 else
   goto skip_certs;
 
-  {
+ {
   uschar * expcerts;
   if (!expand_check(tls_verify_certificates, US"tls_verify_certificates",
 		    &expcerts, errstr))
@@ -3040,7 +3162,7 @@ else
 
   if (expcerts && *expcerts)
     setup_cert_verify(ctx, server_verify_optional, verify_callback_server);
-  }
+ }
 skip_certs: ;
 
 #ifndef DISABLE_TLS_RESUME
@@ -3167,6 +3289,33 @@ if (SSL_session_reused(ssl))
   }
 #endif
 
+#ifdef EXIM_HAVE_ALPN
+/* If require-alpn, check server_seen_alpn here.  Else abort TLS */
+if (!tls_alpn || !*tls_alpn)
+  { DEBUG(D_tls) debug_printf("TLS: was not watching for ALPN\n"); }
+else if (!server_seen_alpn)
+  if (verify_check_host(&hosts_require_alpn) == OK)
+    {
+    /* We'd like to send a definitive Alert but OpenSSL provides no facility */
+    SSL_shutdown(ssl);
+    tls_error(US"handshake", NULL, US"ALPN required but not negotiated", errstr);
+    return FAIL;
+    }
+  else
+    { DEBUG(D_tls) debug_printf("TLS: no ALPN presented in handshake\n"); }
+else DEBUG(D_tls)
+  {
+  const uschar * name;
+  unsigned len;
+  SSL_get0_alpn_selected(ssl, &name, &len);
+  if (len && name)
+    debug_printf("ALPN negotiated: '%.*s'\n", (int)*name, name+1);
+  else
+    debug_printf("ALPN: no protocol negotiated\n");
+  }
+#endif
+
+
 /* TLS has been set up. Record data for the connection,
 adjust the input functions to read via TLS, and initialize things. */
 
@@ -3235,10 +3384,10 @@ ssl_xfer_eof = ssl_xfer_error = FALSE;
 receive_getc = tls_getc;
 receive_getbuf = tls_getbuf;
 receive_get_cache = tls_get_cache;
+receive_hasc = tls_hasc;
 receive_ungetc = tls_ungetc;
 receive_feof = tls_feof;
 receive_ferror = tls_ferror;
-receive_smtp_buffered = tls_smtp_buffered;
 
 tls_in.active.sock = fileno(smtp_out);
 tls_in.active.tls_ctx = NULL;	/* not using explicit ctx for server-side */
@@ -3274,7 +3423,7 @@ else if (verify_check_given_host(CUSS &ob->tls_try_verify_hosts, host) == OK)
 else
   return OK;
 
-  {
+ {
   uschar * expcerts;
   if (!expand_check(ob->tls_verify_certificates, US"tls_verify_certificates",
 		    &expcerts, errstr))
@@ -3289,7 +3438,7 @@ else
 
   if (expcerts && *expcerts)
     setup_cert_verify(ctx, client_verify_optional, verify_callback_client);
-  }
+ }
 
 if (verify_check_given_host(CUSS &ob->tls_verify_cert_hostnames, host) == OK)
   {
@@ -3397,29 +3546,35 @@ if (tlsp->host_resumable)
 	  debug_printf("decoding session: %s\n", ssl_errstring);
 	  }
 	}
-#ifdef EXIM_HAVE_SESSION_TICKET
-      else if ( SSL_SESSION_get_ticket_lifetime_hint(ss) + dt->time_stamp
-	       < time(NULL))
+      else
 	{
-	DEBUG(D_tls) debug_printf("session expired\n");
-	dbfn_delete(dbm_file, key);
-	}
+	unsigned long lifetime =
+#ifdef EXIM_HAVE_SESSION_TICKET
+	  SSL_SESSION_get_ticket_lifetime_hint(ss);
+#else			/* Use, fairly arbitrilarily, what we as server would */
+	  f.running_in_test_harness ? 6 : ssl_session_timeout;
 #endif
-      else if (!SSL_set_session(ssl, ss))
-	{
-	DEBUG(D_tls)
+	if (lifetime + dt->time_stamp < time(NULL))
 	  {
-	  ERR_error_string_n(ERR_get_error(),
-	    ssl_errstring, sizeof(ssl_errstring));
-	  debug_printf("applying session to ssl: %s\n", ssl_errstring);
+	  DEBUG(D_tls) debug_printf("session expired\n");
+	  dbfn_delete(dbm_file, key);
+	  }
+	else if (!SSL_set_session(ssl, ss))
+	  {
+	  DEBUG(D_tls)
+	    {
+	    ERR_error_string_n(ERR_get_error(),
+	      ssl_errstring, sizeof(ssl_errstring));
+	    debug_printf("applying session to ssl: %s\n", ssl_errstring);
+	    }
+	  }
+	else
+	  {
+	  DEBUG(D_tls) debug_printf("good session\n");
+	  tlsp->resumption |= RESUME_CLIENT_SUGGESTED;
+	  tlsp->verify_override = dt->verify_override;
+	  tlsp->ocsp = dt->ocsp;
 	  }
-	}
-      else
-	{
-	DEBUG(D_tls) debug_printf("good session\n");
-	tlsp->resumption |= RESUME_CLIENT_SUGGESTED;
-	tlsp->verify_override = dt->verify_override;
-	tlsp->ocsp = dt->ocsp;
 	}
       }
     else
@@ -3528,6 +3683,47 @@ if (SSL_session_reused(exim_client_ctx->ssl))
 #endif	/* !DISABLE_TLS_RESUME */
 
 
+#ifdef EXIM_HAVE_ALPN
+/* Expand and convert an Exim list to an ALPN list.  False return for fail.
+NULL plist return for silent no-ALPN.
+*/
+
+static BOOL
+tls_alpn_plist(const uschar * tls_alpn, const uschar ** plist, unsigned * plen,
+  uschar ** errstr)
+{
+uschar * exp_alpn;
+
+if (!expand_check(tls_alpn, US"tls_alpn", &exp_alpn, errstr))
+  return FALSE;
+
+if (!exp_alpn)
+  {
+  DEBUG(D_tls) debug_printf("Setting TLS ALPN forced to fail, not sending\n");
+  *plist = NULL;
+  }
+else
+  {
+  /* The server implementation only accepts exactly one protocol name
+  but it's little extra code complexity in the client. */
+
+  const uschar * list = exp_alpn;
+  uschar * p = store_get(Ustrlen(exp_alpn), is_tainted(exp_alpn)), * s, * t;
+  int sep = 0;
+  uschar len;
+
+  for (t = p; s = string_nextinlist(&list, &sep, NULL, 0); t += len)
+    {
+    *t++ = len = (uschar) Ustrlen(s);
+    memcpy(t, s, len);
+    }
+  *plist = (*plen = t - p) ? p : NULL;
+  }
+return TRUE;
+}
+#endif	/* EXIM_HAVE_ALPN */
+
+
 /*************************************************
 *    Start a TLS session in a client             *
 *************************************************/
@@ -3713,6 +3909,28 @@ if (ob->tls_sni)
     }
   }
 
+if (ob->tls_alpn)
+#ifdef EXIM_HAVE_ALPN
+  {
+  const uschar * plist;
+  unsigned plen;
+
+  if (!tls_alpn_plist(ob->tls_alpn, &plist, &plen, errstr))
+    return FALSE;
+  if (plist)
+    if (SSL_set_alpn_protos(exim_client_ctx->ssl, plist, plen) != 0)
+      {
+      tls_error(US"alpn init", host, NULL, errstr);
+      return FALSE;
+      }
+    else
+      DEBUG(D_tls) debug_printf("Setting TLS ALPN '%s'\n", ob->tls_alpn);
+  }
+#else
+  log_write(0, LOG_MAIN, "ALPN unusable with this OpenSSL library version; ignoring \"%s\"\n",
+          ob->tls_alpn);
+#endif
+
 #ifdef SUPPORT_DANE
 if (conn_args->dane)
   if (dane_tlsa_load(exim_client_ctx->ssl, host, &conn_args->tlsa_dnsa, errstr) != OK)
@@ -3792,6 +4010,24 @@ DEBUG(D_tls)
 tls_client_resume_posthandshake(exim_client_ctx, tlsp);
 #endif
 
+#ifdef EXIM_HAVE_ALPN
+if (ob->tls_alpn)	/* We requested. See what was negotiated. */
+  {
+  const uschar * name;
+  unsigned len;
+
+  SSL_get0_alpn_selected(exim_client_ctx->ssl, &name, &len);
+  if (len > 0)
+    { DEBUG(D_tls) debug_printf("ALPN negotiated %u: '%.*s'\n", len, (int)*name, name+1); }
+  else if (verify_check_given_host(CUSS &ob->hosts_require_alpn, host) == OK)
+    {
+    /* Would like to send a relevant fatal Alert, but OpenSSL has no API */
+    tls_error(US"handshake", host, US"ALPN required but not negotiated", errstr);
+    return FALSE;
+    }
+  }
+#endif
+
 #ifdef SSL_get_extms_support
 tlsp->ext_master_secret = SSL_get_extms_support(exim_client_ctx->ssl) == 1;
 #endif
@@ -3924,6 +4160,12 @@ if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
 }
 
+BOOL
+tls_hasc(void)
+{
+return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm;
+}
+
 uschar *
 tls_getbuf(unsigned * len)
 {
@@ -3948,10 +4190,13 @@ return buf;
 
 
 void
-tls_get_cache(void)
+tls_get_cache(unsigned lim)
 {
 #ifndef DISABLE_DKIM
 int n = ssl_xfer_buffer_hwm - ssl_xfer_buffer_lwm;
+debug_printf("tls_get_cache\n");
+if (n > lim)
+  n = lim;
 if (n > 0)
   dkim_exim_verify_feed(ssl_xfer_buffer+ssl_xfer_buffer_lwm, n);
 #endif
@@ -3959,7 +4204,7 @@ if (n > 0)
 
 
 BOOL
-tls_could_read(void)
+tls_could_getc(void)
 {
 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm
     || SSL_pending(state_server.lib_state.lib_ssl) > 0;
@@ -4210,10 +4455,10 @@ if (!o_ctx)		/* server side */
   receive_getc =	smtp_getc;
   receive_getbuf =	smtp_getbuf;
   receive_get_cache =	smtp_get_cache;
+  receive_hasc =	smtp_hasc;
   receive_ungetc =	smtp_ungetc;
   receive_feof =	smtp_feof;
   receive_ferror =	smtp_ferror;
-  receive_smtp_buffered = smtp_buffered;
   tls_in.active.tls_ctx = NULL;
   tls_in.sni = NULL;
   /* Leave bits, peercert, cipher, peerdn, certificate_verified set, for logging */
@@ -4464,7 +4709,6 @@ tls_openssl_options_parse(uschar *option_spec, long *results)
 {
 long result, item;
 uschar * exp, * end;
-uschar keep_c;
 BOOL adding, item_parsed;
 
 /* Server: send no (<= TLS1.2) session tickets */
@@ -4506,11 +4750,8 @@ for (uschar * s = exp; *s; /**/)
     return FALSE;
     }
   adding = *s++ == '+';
-  for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
-  keep_c = *end;
-  *end = '\0';
-  item_parsed = tls_openssl_one_option_parse(s, &item);
-  *end = keep_c;
+  for (end = s; *end && !isspace(*end); ) end++;
+  item_parsed = tls_openssl_one_option_parse(string_copyn(s, end-s), &item);
   if (!item_parsed)
     {
     DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"\n", s);