Merge remote-tracking branch 'restricted/pr/403' into development-restricted

* restricted/pr/403:
  Correct record header size in case of TLS
  Don't allocate space for DTLS header if DTLS is disabled
  Improve debugging output
  Adapt ChangeLog
  Add run-time check for handshake message size in ssl_write_record
  Add run-time check for record content size in ssl_encrypt_buf
  Add compile-time checks for size of record content and payload

ChangeLog

@@ -83,6 +83,8 @@ Bugfix
      Reported by Yolan Romailler.
    * Fix word size check in in pk.c to not depend on MBEDTLS_HAVE_INT64.
    * Fix incorrect unit in benchmark output. #850
+   * Add size-checks for record and handshake message content, securing
+     fragile yet non-exploitable code-paths.
 
 Changes
    * Extend cert_write example program by options to set the CRT version

include/mbedtls/ssl_internal.h

@@ -24,6 +24,7 @@
 #define MBEDTLS_SSL_INTERNAL_H
 
 #include "ssl.h"
+#include "cipher.h"
 
 #if defined(MBEDTLS_MD5_C)
 #include "md5.h"
@@ -138,13 +139,33 @@
 #define MBEDTLS_SSL_PADDING_ADD              0
 #endif
 
-#define MBEDTLS_SSL_BUFFER_LEN  ( MBEDTLS_SSL_MAX_CONTENT_LEN               \
-                        + MBEDTLS_SSL_COMPRESSION_ADD               \
-                        + 29 /* counter + header + IV */    \
-                        + MBEDTLS_SSL_MAC_ADD                       \
-                        + MBEDTLS_SSL_PADDING_ADD                   \
+#define MBEDTLS_SSL_PAYLOAD_LEN ( MBEDTLS_SSL_MAX_CONTENT_LEN    \
+                        + MBEDTLS_SSL_COMPRESSION_ADD            \
+                        + MBEDTLS_MAX_IV_LENGTH                  \
+                        + MBEDTLS_SSL_MAC_ADD                    \
+                        + MBEDTLS_SSL_PADDING_ADD                \
                         )
 
+/*
+ * Check that we obey the standard's message size bounds
+ */
+
+#if MBEDTLS_SSL_MAX_CONTENT_LEN > 16384
+#error Bad configuration - record content too large.
+#endif
+
+#if MBEDTLS_SSL_PAYLOAD_LEN > 16384 + 2048
+#error Bad configuration - protected record payload too large.
+#endif
+
+/* Note: Even though the TLS record header is only 5 bytes
+   long, we're internally using 8 bytes to store the
+   implicit sequence number. */
+#define MBEDTLS_SSL_HEADER_LEN 13
+
+#define MBEDTLS_SSL_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_PAYLOAD_LEN ) )
+
 /*
  * TLS extension flags (for extensions with outgoing ServerHello content
  * that need it (e.g. for RENEGOTIATION_INFO the server already knows because

library/ssl_tls.c

@@ -1268,6 +1268,14 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl )
     MBEDTLS_SSL_DEBUG_BUF( 4, "before encrypt: output payload",
                       ssl->out_msg, ssl->out_msglen );
 
+    if( ssl->out_msglen > MBEDTLS_SSL_MAX_CONTENT_LEN )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "Record content %u too large, maximum %d",
+                                    (unsigned) ssl->out_msglen,
+                                    MBEDTLS_SSL_MAX_CONTENT_LEN ) );
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+    }
+
     /*
      * Add MAC before if needed
      */
@@ -2733,6 +2741,15 @@ int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl )
         if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
         {
             /* Make room for the additional DTLS fields */
+            if( MBEDTLS_SSL_MAX_CONTENT_LEN - ssl->out_msglen < 8 )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "DTLS handshake message too large: "
+                              "size %u, maximum %u",
+                               (unsigned) ( ssl->in_hslen - 4 ),
+                               (unsigned) ( MBEDTLS_SSL_MAX_CONTENT_LEN - 12 ) ) );
+                return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+            }
+
             memmove( ssl->out_msg + 12, ssl->out_msg + 4, len - 4 );
             ssl->out_msglen += 8;
             len += 8;