Added bounds checking for TLS extensions

IOTSSL-478 - Added checks to prevent buffer overflows.

library/ssl_cli.c

@@ -60,6 +60,7 @@ static void ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
                                     size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
     size_t hostname_len;
 
     *olen = 0;
@@ -72,6 +73,13 @@ static void ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
 
     hostname_len = strlen( ssl->hostname );
 
+    if( (size_t)(end - p) < hostname_len + 9 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small for hostname" ) );
+        return;
+    }
+
+
     /*
      * struct {
      *     NameType name_type;
@@ -115,6 +123,7 @@ static void ssl_write_renegotiation_ext( mbedtls_ssl_context *ssl,
                                          size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     *olen = 0;
 
@@ -123,6 +132,12 @@ static void ssl_write_renegotiation_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding renegotiation extension" ) );
 
+    if( (size_t)(end - p) < 5 + ssl->verify_data_len )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     /*
      * Secure renegotiation
      */
@@ -149,6 +164,7 @@ static void ssl_write_signature_algorithms_ext( mbedtls_ssl_context *ssl,
                                                 size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
     size_t sig_alg_len = 0;
     const int *md;
 #if defined(MBEDTLS_RSA_C) || defined(MBEDTLS_ECDSA_C)
@@ -162,9 +178,27 @@ static void ssl_write_signature_algorithms_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding signature_algorithms extension" ) );
 
+    for( md = ssl->conf->sig_hashes; *md != MBEDTLS_MD_NONE; md++ )
+    {
+#if defined(MBEDTLS_ECDSA_C)
+        sig_alg_len += 2;
+#endif
+#if defined(MBEDTLS_RSA_C)
+        sig_alg_len += 2;
+#endif
+    }
+
+    if( (size_t)(end - p) < sig_alg_len + 6 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     /*
      * Prepare signature_algorithms extension (TLS 1.2)
      */
+    sig_alg_len = 0;
+
     for( md = ssl->conf->sig_hashes; *md != MBEDTLS_MD_NONE; md++ )
     {
 #if defined(MBEDTLS_ECDSA_C)
@@ -214,6 +248,7 @@ static void ssl_write_supported_elliptic_curves_ext( mbedtls_ssl_context *ssl,
                                                      size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
     unsigned char *elliptic_curve_list = p + 6;
     size_t elliptic_curve_len = 0;
     const mbedtls_ecp_curve_info *info;
@@ -227,6 +262,25 @@ static void ssl_write_supported_elliptic_curves_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_elliptic_curves extension" ) );
 
+#if defined(MBEDTLS_ECP_C)
+    for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
+    {
+        info = mbedtls_ecp_curve_info_from_grp_id( *grp_id );
+#else
+    for( info = mbedtls_ecp_curve_list(); info->grp_id != MBEDTLS_ECP_DP_NONE; info++ )
+    {
+#endif
+        elliptic_curve_len += 2;
+    }
+
+    if( (size_t)(end - p) < 6 + elliptic_curve_len )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
+    elliptic_curve_len = 0;
+
 #if defined(MBEDTLS_ECP_C)
     for( grp_id = ssl->conf->curve_list; *grp_id != MBEDTLS_ECP_DP_NONE; grp_id++ )
     {
@@ -260,12 +314,18 @@ static void ssl_write_supported_point_formats_ext( mbedtls_ssl_context *ssl,
                                                    size_t *olen )
 {
     unsigned char *p = buf;
-    ((void) ssl);
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     *olen = 0;
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported_point_formats extension" ) );
 
+    if( (size_t)(end - p) < 6 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS      ) & 0xFF );
 
@@ -285,6 +345,7 @@ static void ssl_write_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                                size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     if( ssl->conf->mfl_code == MBEDTLS_SSL_MAX_FRAG_LEN_NONE ) {
         *olen = 0;
@@ -293,6 +354,12 @@ static void ssl_write_max_fragment_length_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding max_fragment_length extension" ) );
 
+    if( (size_t)(end - p) < 5 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_MAX_FRAGMENT_LENGTH      ) & 0xFF );
 
@@ -310,6 +377,7 @@ static void ssl_write_truncated_hmac_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf, size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED )
     {
@@ -319,6 +387,12 @@ static void ssl_write_truncated_hmac_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding truncated_hmac extension" ) );
 
+    if( (size_t)(end - p) < 4 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
 
@@ -334,6 +408,7 @@ static void ssl_write_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                        unsigned char *buf, size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     if( ssl->conf->encrypt_then_mac == MBEDTLS_SSL_ETM_DISABLED ||
         ssl->conf->max_minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
@@ -345,6 +420,12 @@ static void ssl_write_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding encrypt_then_mac "
                         "extension" ) );
 
+    if( (size_t)(end - p) < 4 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC      ) & 0xFF );
 
@@ -360,6 +441,7 @@ static void ssl_write_extended_ms_ext( mbedtls_ssl_context *ssl,
                                        unsigned char *buf, size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
 
     if( ssl->conf->extended_ms == MBEDTLS_SSL_EXTENDED_MS_DISABLED ||
         ssl->conf->max_minor_ver == MBEDTLS_SSL_MINOR_VERSION_0 )
@@ -371,6 +453,12 @@ static void ssl_write_extended_ms_ext( mbedtls_ssl_context *ssl,
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding extended_master_secret "
                         "extension" ) );
 
+    if( (size_t)(end - p) < 4 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET      ) & 0xFF );
 
@@ -386,6 +474,7 @@ static void ssl_write_session_ticket_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf, size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
     size_t tlen = ssl->session_negotiate->ticket_len;
 
     if( ssl->conf->session_tickets == MBEDTLS_SSL_SESSION_TICKETS_DISABLED )
@@ -396,6 +485,12 @@ static void ssl_write_session_ticket_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding session ticket extension" ) );
 
+    if( (size_t)(end - p) < 4 + tlen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_SESSION_TICKET      ) & 0xFF );
 
@@ -404,8 +499,7 @@ static void ssl_write_session_ticket_ext( mbedtls_ssl_context *ssl,
 
     *olen = 4;
 
-    if( ssl->session_negotiate->ticket == NULL ||
+    if( ssl->session_negotiate->ticket == NULL || tlen == 0 )
-        ssl->session_negotiate->ticket_len == 0 )
     {
         return;
     }
@@ -423,6 +517,8 @@ static void ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                                 unsigned char *buf, size_t *olen )
 {
     unsigned char *p = buf;
+    const unsigned char *end = ssl->out_msg + MBEDTLS_SSL_MAX_CONTENT_LEN;
+    size_t alpnlen = 0;
     const char **cur;
 
     if( ssl->conf->alpn_list == NULL )
@@ -433,6 +529,15 @@ static void ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
 
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding alpn extension" ) );
 
+    for( cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
+        alpnlen +=   *p = (unsigned char)( strlen( *cur ) & 0xFF );
+
+    if( (size_t)(end - p) < 6 + alpnlen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small" ) );
+        return;
+    }
+
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN >> 8 ) & 0xFF );
     *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_ALPN      ) & 0xFF );