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From 83c9f495ffe70c7dd280b41fdfd4881485a3bc28 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Mon, 26 Jun 2017 13:52:14 +0100
Subject: [PATCH] Prevent bounds check bypass through overflow in PSK identity
parsing
The check `if( *p + n > end )` in `ssl_parse_client_psk_identity` is
unsafe because `*p + n` might overflow, thus bypassing the check. As
`n` is a user-specified value up to 65K, this is relevant if the
library happens to be located in the last 65K of virtual memory.
This commit replaces the check by a safe version.
---
library/ssl_srv.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3223,7 +3223,7 @@ static int ssl_parse_client_psk_identity
/*
* Receive client pre-shared key identity name
*/
- if( *p + 2 > end )
+ if( end - *p < 2 )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
@@ -3232,7 +3232,7 @@ static int ssl_parse_client_psk_identity
n = ( (*p)[0] << 8 ) | (*p)[1];
*p += 2;
- if( n < 1 || n > 65535 || *p + n > end )
+ if( n < 1 || n > 65535 || n > (size_t) ( end - *p ) )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client key exchange message" ) );
return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE );
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