Merge remote-tracking branch 'origin/pr/2390' into mbedtls-2.7

* origin/pr/2390:
  Correct length check for DTLS records from old epochs.

library/ssl_tls.c

@@ -3702,81 +3702,23 @@ static int ssl_parse_record_header( mbedtls_ssl_context *ssl )
         return( MBEDTLS_ERR_SSL_INVALID_RECORD );
     }
 
-    /* Check length against bounds of the current transform and version */
-    if( ssl->transform_in == NULL )
-    {
-        if( ssl->in_msglen < 1 ||
-            ssl->in_msglen > MBEDTLS_SSL_MAX_CONTENT_LEN )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
-            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
-        }
-    }
-    else
-    {
-        if( ssl->in_msglen < ssl->transform_in->minlen )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
-            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
-        }
-
-#if defined(MBEDTLS_SSL_PROTO_SSL3)
-        if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 &&
-            ssl->in_msglen > ssl->transform_in->minlen + MBEDTLS_SSL_MAX_CONTENT_LEN )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
-            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
-        }
-#endif
-#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
-    defined(MBEDTLS_SSL_PROTO_TLS1_2)
-        /*
-         * TLS encrypted messages can have up to 256 bytes of padding
-         */
-        if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 &&
-            ssl->in_msglen > ssl->transform_in->minlen +
-                             MBEDTLS_SSL_MAX_CONTENT_LEN + 256 )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
-            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
-        }
-#endif
-    }
-
     /*
-     * DTLS-related tests done last, because most of them may result in
-     * silently dropping the record (but not the whole datagram), and we only
-     * want to consider that after ensuring that the "basic" fields (type,
-     * version, length) are sane.
+     * DTLS-related tests.
+     * Check epoch before checking length constraint because
+     * the latter varies with the epoch. E.g., if a ChangeCipherSpec
+     * message gets duplicated before the corresponding Finished message,
+     * the second ChangeCipherSpec should be discarded because it belongs
+     * to an old epoch, but not because its length is shorter than
+     * the minimum record length for packets using the new record transform.
+     * Note that these two kinds of failures are handled differently,
+     * as an unexpected record is silently skipped but an invalid
+     * record leads to the entire datagram being dropped.
      */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
     {
         unsigned int rec_epoch = ( ssl->in_ctr[0] << 8 ) | ssl->in_ctr[1];
 
-        /* Drop unexpected ChangeCipherSpec messages */
-        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
-            ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
-            ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ChangeCipherSpec" ) );
-            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
-        }
-
-        /* Drop unexpected ApplicationData records,
-         * except at the beginning of renegotiations */
-        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_APPLICATION_DATA &&
-            ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER
-#if defined(MBEDTLS_SSL_RENEGOTIATION)
-            && ! ( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
-                   ssl->state == MBEDTLS_SSL_SERVER_HELLO )
-#endif
-            )
-        {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ApplicationData" ) );
-            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
-        }
-
         /* Check epoch (and sequence number) with DTLS */
         if( rec_epoch != ssl->in_epoch )
         {
@@ -3816,9 +3758,74 @@ static int ssl_parse_record_header( mbedtls_ssl_context *ssl )
             return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
         }
 #endif
+
+        /* Drop unexpected ChangeCipherSpec messages */
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
+            ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
+            ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ChangeCipherSpec" ) );
+            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
+        }
+
+        /* Drop unexpected ApplicationData records,
+         * except at the beginning of renegotiations */
+        if( ssl->in_msgtype == MBEDTLS_SSL_MSG_APPLICATION_DATA &&
+            ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+            && ! ( ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS &&
+                   ssl->state == MBEDTLS_SSL_SERVER_HELLO )
+#endif
+            )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ApplicationData" ) );
+            return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
+        }
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
+
+    /* Check length against bounds of the current transform and version */
+    if( ssl->transform_in == NULL )
+    {
+        if( ssl->in_msglen < 1 ||
+            ssl->in_msglen > MBEDTLS_SSL_MAX_CONTENT_LEN )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+    }
+    else
+    {
+        if( ssl->in_msglen < ssl->transform_in->minlen )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+        if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 &&
+            ssl->in_msglen > ssl->transform_in->minlen + MBEDTLS_SSL_MAX_CONTENT_LEN )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+#endif
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        /*
+         * TLS encrypted messages can have up to 256 bytes of padding
+         */
+        if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_1 &&
+            ssl->in_msglen > ssl->transform_in->minlen +
+                             MBEDTLS_SSL_MAX_CONTENT_LEN + 256 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+#endif
+    }
+
     return( 0 );
 }
 

tests/ssl-opt.sh

@@ -5137,8 +5137,8 @@ run_test    "DTLS proxy: duplicate every packet" \
             0 \
             -c "replayed record" \
             -s "replayed record" \
-            -c "discarding invalid record" \
-            -s "discarding invalid record" \
+            -c "record from another epoch" \
+            -s "record from another epoch" \
             -S "resend" \
             -s "Extra-header:" \
             -c "HTTP/1.0 200 OK"
@@ -5150,8 +5150,8 @@ run_test    "DTLS proxy: duplicate every packet, server anti-replay off" \
             0 \
             -c "replayed record" \
             -S "replayed record" \
-            -c "discarding invalid record" \
-            -s "discarding invalid record" \
+            -c "record from another epoch" \
+            -s "record from another epoch" \
             -c "resend" \
             -s "resend" \
             -s "Extra-header:" \
@@ -5212,8 +5212,6 @@ run_test    "DTLS proxy: delay ChangeCipherSpec" \
             0 \
             -c "record from another epoch" \
             -s "record from another epoch" \
-            -c "discarding invalid record" \
-            -s "discarding invalid record" \
             -s "Extra-header:" \
             -c "HTTP/1.0 200 OK"