* Rewrite support for specific SSL encryption protocols, including

	a. Add a new variable: encryption-protocol-range, which can be
	   used to specify the minimum and maximum versions of the TLS
	   protocol that Alpine will attempt to use to encrypt its
	   communication with the server.
	b. Add support for the Server Name Identification (SNI) extension
	   needed for TLSv1.3.
	c. Remove the DTLS code. It was not being used.

1 files changed, 99 insertions, 69 deletions

diff --git a/imap/src/osdep/unix/ssl_unix.c b/imap/src/osdep/unix/ssl_unix.c
index efbe8392..11454cbd 100644
--- a/imap/src/osdep/unix/ssl_unix.c
+++ b/imap/src/osdep/unix/ssl_unix.c
@@ -33,42 +33,10 @@
 #include <bio.h>
 #include <crypto.h>
 #include <rand.h>
-#ifndef TLS_client_method
-#ifdef TLSv1_2_client_method
-#define TLS_client_method TLSv1_2_client_method
-#elif defined(TLSv1_1_client_method)
-#define TLS_client_method TLSv1_1_client_method
-#else 
-#define TLS_client_method TLSv1_client_method
-#endif /* TLSv1_2_client_method */
-#endif /* TLS_client_method */
 #ifdef OPENSSL_1_1_0
 #include <rsa.h>
 #include <bn.h>
-#ifdef TLSv1_client_method
-#undef TLSv1_client_method
-#endif /* TLSv1_client_method */
-#ifdef TLSv1_1_client_method
-#undef TLSv1_1_client_method
-#endif /* TLSv1_1_client_method */
-#ifdef TLSv1_2_client_method
-#undef TLSv1_2_client_method
-#endif /* TLSv1_2_client_method */
-#ifdef DTLSv1_client_method
-#undef DTLSv1_client_method
-#endif /* DTLSv1_client_method */
-#ifdef DTLSv1_2_client_method
-#undef DTLSv1_2_client_method
-#endif /* DTLSv1_2_client_method */
-#define TLSv1_client_method   TLS_client_method
-#define TLSv1_1_client_method TLS_client_method
-#define TLSv1_2_client_method TLS_client_method
-#define DTLSv1_client_method  DTLS_client_method
-#define DTLSv1_2_client_method DTLS_client_method
 #endif /* OPENSSL_1_1_0 */
-#ifndef DTLSv1_2_client_method
-#define DTLSv1_2_client_method DTLSv1_client_method
-#endif /* DTLSv1_2_client_method */
 #undef STRING
 #undef crypt
 
@@ -105,7 +73,8 @@ typedef struct ssl_stream {
 #include "sslio.h"
 
 /* Function prototypes */
-const SSL_METHOD *ssl_connect_mthd(int flag);
+int ssl_disable_mask(int ssl_version, int direction);
+const SSL_METHOD *ssl_connect_mthd(int flag, int *min, int *max);
 static SSLSTREAM *ssl_start(TCPSTREAM *tstream,char *host,unsigned long flags);
 static char *ssl_start_work (SSLSTREAM *stream,char *host,unsigned long flags);
 static int ssl_open_verify (int ok,X509_STORE_CTX *ctx);
@@ -205,50 +174,95 @@ SSLSTREAM *ssl_aopen (NETMBX *mb,char *service,char *usrbuf)
   return NIL;			/* don't use this mechanism with SSL */
 }
 
+typedef struct ssl_disable_s {
+  int   version;
+  int   disable_code;
+} SSL_DISABLE_S;
+        
+SSL_DISABLE_S ssl_disable[] = {
+    {SSL2_VERSION, SSL_OP_NO_SSLv2},
+    {SSL3_VERSION, SSL_OP_NO_SSLv3},
+    {TLS1_VERSION, SSL_OP_NO_TLSv1},
+    {TLS1_1_VERSION, SSL_OP_NO_TLSv1_1},
+    {TLS1_2_VERSION, SSL_OP_NO_TLSv1_2},
+#ifdef TLS1_3_VERSION
+    {TLS1_3_VERSION, SSL_OP_NO_TLSv1_3},
+#endif /* TLS1_3_VERSION */
+    {0, 0}
+};
+
+#define NUMBER_SSL_VERSIONS (sizeof(ssl_disable)/sizeof(ssl_disable[0]) - 1)
+
+/* returns the mask to disable a specific version.
+ * If version not found, returns 0.
+ * 
+ * Arguments: version, and direction.
+ * If direction is -1, returns mask to disable versions less than given version.
+ * If direction is +1, returns mask to disable versions bigger than given version.
+ */
+int ssl_disable_mask(int ssl_version, int direction)
+{
+  int rv = 0;
+  int i;
+  for(i = 0; ssl_disable[i].version != 0 
+		&& ssl_disable[i].version != ssl_version; i++);
+  if(i == 0 
+     || i == NUMBER_SSL_VERSIONS - 1 
+     || ssl_disable[i].version == 0) 
+    return rv;
+  i += direction; 	/* move in the direction */
+  for(; i >= 0 && i <= NUMBER_SSL_VERSIONS - 1; i += direction)
+     rv |= ssl_disable[i].disable_code;
+  return rv;
+}
+
+
 /* ssl_connect_mthd: returns a context pointer to the connection to
  * a ssl server
  */
-const SSL_METHOD *ssl_connect_mthd(int flag)
+const SSL_METHOD *ssl_connect_mthd(int flag, int *min, int *max)
 {
-  if (flag & NET_TRYTLS1)
-#ifndef OPENSSL_NO_TLS1_METHOD
-     return TLSv1_client_method();
+  char tmp[10000];
+  int client_request;
+  client_request = (flag & NET_TRYTLS1) ? TLS1_VERSION
+		 : (flag & NET_TRYTLS1_1) ? TLS1_1_VERSION
+		 : (flag & NET_TRYTLS1_2) ? TLS1_2_VERSION
+#ifdef TLS1_3_VERSION
+		 : (flag & NET_TRYTLS1_3) ? TLS1_3_VERSION
 #else
-     return TLS_client_method();
-#endif /* OPENSSL_NO_TLS1_METHOD */
-
-  else if(flag & NET_TRYTLS1_1)
-#ifndef OPENSSL_NO_TLS1_1_METHOD
+		 : (flag & NET_TRYTLS1_3) ? INT_MAX
+#endif
+		 : 0L;
+
+  *min = *(int *) mail_parameters(NULL, GET_ENCRYPTION_RANGE_MIN, NULL);
+  *max = *(int *) mail_parameters(NULL, GET_ENCRYPTION_RANGE_MAX, NULL);
+
+  /* 
+   * if no special request, negotiate the maximum the client is configured
+   * to negotiate
+   */
+  if(client_request == 0)
+    client_request = *max;
+
+  if(client_request < *min || client_request > *max)
+    return NIL;		/* out of range? bail out */
+
+#ifndef OPENSSL_1_1_0
+  if(client_request == SSL3_VERSION)
+     return SSLv3_client_method();
+  if(client_request == TLS1_VERSION)
+     return TLSv1_client_method();
+  else if(client_request == TLS1_1_VERSION)
      return TLSv1_1_client_method();
-#else
-     return TLS_client_method();
-#endif /* OPENSSL_NO_TLS1_1_METHOD */
-
-  else if(flag & NET_TRYTLS1_2)
-#ifndef OPENSSL_NO_TLS1_2_METHOD
+  else if(client_request == TLS1_2_VERSION)
      return TLSv1_2_client_method();
-#else
-     return TLS_client_method();
-#endif /* OPENSSL_NO_TLS1_2_METHOD */
-
-  else if(flag & NET_TRYTLS1_3)
+#ifdef TLS1_3_VERSION	/* this is only reachable if TLS1_3 support exists */
+  else if(client_request == TLS1_3_VERSION)
      return TLS_client_method();
+#endif /* TLS1_3_VERSION */
+#endif /* ifndef OPENSSL_1_1_0 */
 
-  else if(flag & NET_TRYDTLS1)
-#ifndef OPENSSL_NO_DTLS1_METHOD
-     return DTLSv1_client_method();
-#else
-     return DTLS_client_method();
-#endif /* OPENSSL_NO_DTLS1_METHOD */
-
-  else if(flag & NET_TRYDTLS1_2)
-#ifndef OPENSSL_NO_DTLS1_METHOD
-     return DTLSv1_2_client_method();
-#else
-     return DTLS_client_method();
-#endif /* OPENSSL_NO_DTLS1_METHOD */
-
-  else return SSLv23_client_method();
+  return SSLv23_client_method();
 }
 
 /* Start SSL/TLS negotiations
@@ -317,6 +331,7 @@ static char *ssl_start_work (SSLSTREAM *stream,char *host,unsigned long flags)
   BIO *bio;
   X509 *cert;
   unsigned long sl,tl;
+  int min, max;
   char *s,*t,*err,tmp[MAILTMPLEN], buf[256];
   sslcertificatequery_t scq =
     (sslcertificatequery_t) mail_parameters (NIL,GET_SSLCERTIFICATEQUERY,NIL);
@@ -326,9 +341,21 @@ static char *ssl_start_work (SSLSTREAM *stream,char *host,unsigned long flags)
     (sslclientkey_t) mail_parameters (NIL,GET_SSLCLIENTKEY,NIL);
   if (ssl_last_error) fs_give ((void **) &ssl_last_error);
   ssl_last_host = host;
-  if (!(stream->context = SSL_CTX_new (ssl_connect_mthd(flags))))
+  if (!(stream->context = SSL_CTX_new (ssl_connect_mthd(flags, &min, &max))))
     return "SSL context failed";
   SSL_CTX_set_options (stream->context,0);
+#ifdef OPENSSL_1_1_0
+  if(stream->context != NIL &&
+     ((min != 0 && SSL_CTX_set_min_proto_version(stream->context, min) == 0) ||
+      (max != 0 && SSL_CTX_set_max_proto_version(stream->context, max) == 0)))
+    return "SSL set protocol version Failed";
+#else
+  { int masklow, maskhigh;
+    masklow = ssl_disable_mask(min, -1);
+    maskhigh = ssl_disable_mask(max, 1);
+    SSL_CTX_set_options(stream->context, masklow|maskhigh);
+  }
+#endif /* OPENSSL_1_1_0 */
 				/* disable certificate validation? */
   if (flags & NET_NOVALIDATECERT)
     SSL_CTX_set_verify (stream->context,SSL_VERIFY_NONE,NIL);
@@ -363,6 +390,9 @@ static char *ssl_start_work (SSLSTREAM *stream,char *host,unsigned long flags)
 				/* create connection */
   if (!(stream->con = (SSL *) SSL_new (stream->context)))
     return "SSL connection failed";
+  if (host && !SSL_set_tlsext_host_name(stream->con, host)){
+    return "Server Name Identification (SNI) failed";
+  }
   bio = BIO_new_socket (stream->tcpstream->tcpsi,BIO_NOCLOSE);
   SSL_set_bio (stream->con,bio,bio);
   SSL_set_connect_state (stream->con);