From f58c664e2bcf58cc62dd208eaeb98f1481e7d154 Mon Sep 17 00:00:00 2001
From: Ivan Grokhotkov <ivan@espressif.com>
Date: Thu, 19 Apr 2018 11:48:31 +0800
Subject: [PATCH] mbedtls: Add bounds check before signature length read

Part of the patch for CVE-2018-9988.
Cherry-picked from https://github.com/ARMmbed/mbedtls/commit/a1098f81c252b317ad34ea978aea2bc47760b215
Ref. https://github.com/espressif/esp-idf/issues/1860
---
 components/mbedtls/library/ssl_cli.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/components/mbedtls/library/ssl_cli.c b/components/mbedtls/library/ssl_cli.c
index c0ade43ad9..42363f0ead 100644
--- a/components/mbedtls/library/ssl_cli.c
+++ b/components/mbedtls/library/ssl_cli.c
@@ -2470,6 +2470,14 @@ static int ssl_parse_server_key_exchange( mbedtls_ssl_context *ssl )
         /*
          * Read signature
          */
+
+        if( p > end - 2 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server key exchange message" ) );
+            mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                            MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
+            return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_KEY_EXCHANGE );
+        }
         sig_len = ( p[0] << 8 ) | p[1];
         p += 2;