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.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index f137c3d..97d7a9e 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3436,7 +3436,7 @@
/*
* 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 );
@@ -3445,7 +3445,7 @@
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 );
