CBC mode: Allow zero-length message fragments (100% padding)
Fixes
@@ -1979,28 +1979,28 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
* and fake check up to 256 bytes of padding
*/
size_t pad_count = 0, real_count = 1;
- size_t padding_idx = ssl->in_msglen - padlen - 1;
+ size_t padding_idx = ssl->in_msglen - padlen;
size_t i;
/*
* Padding is guaranteed to be incorrect if:
- * 1. padlen >= ssl->in_msglen
+ * 1. padlen > ssl->in_msglen
*
- * 2. padding_idx >= MBEDTLS_SSL_IN_CONTENT_LEN +
+ * 2. padding_idx > MBEDTLS_SSL_IN_CONTENT_LEN +
* ssl->transform_in->maclen
*
* In both cases we reset padding_idx to a safe value (0) to
* prevent out-of-buffer reads.
*/
- correct &= ( ssl->in_msglen >= padlen + 1 );
- correct &= ( padding_idx < MBEDTLS_SSL_IN_CONTENT_LEN +
+ correct &= ( padlen <= ssl->in_msglen );
+ correct &= ( padding_idx <= MBEDTLS_SSL_IN_CONTENT_LEN +
ssl->transform_in->maclen );
padding_idx *= correct;
- for( i = 1; i <= 256; i++ )
+ for( i = 0; i < 256; i++ )
{
- real_count &= ( i <= padlen );
+ real_count &= ( i < padlen );
pad_count += real_count *
( ssl->in_msg[padding_idx + i] == padlen - 1 );
}
