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Latest CBC padding check

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This commit is contained in:
Paul Bakker 2014-07-08 18:30:44 +02:00
parent bbc843f0b8
commit f73b718f17
1 changed files with 22 additions and 6 deletions
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28
library/ssl_tls.c
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@ -1455,17 +1455,33 @@ static int ssl_decrypt_buf( ssl_context *ssl )
* TLSv1+: always check the padding up to the first failure * TLSv1+: always check the padding up to the first failure
* and fake check up to 256 bytes of padding * and fake check up to 256 bytes of padding
*/ */
size_t pad_count = 0, fake_pad_count = 0; 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 - 1;
for( i = 1; i <= padlen; i++ ) /*
pad_count += ( ssl->in_msg[padding_idx + i] == padlen - 1 ); * Padding is guaranteed to be incorrect if:
* 1. padlen >= ssl->in_msglen
*
* 2. padding_idx >= SSL_MAX_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 < SSL_MAX_CONTENT_LEN +
ssl->transform_in->maclen );
for( ; i <= 256; i++ ) padding_idx *= correct;
fake_pad_count += ( ssl->in_msg[padding_idx + i] == padlen - 1 );
for( i = 1; i <= 256; i++ )
{
real_count &= ( i <= padlen );
pad_count += real_count *
( ssl->in_msg[padding_idx + i] == padlen - 1 );
}
correct &= ( pad_count == padlen ); /* Only 1 on correct padding */ correct &= ( pad_count == padlen ); /* Only 1 on correct padding */
correct &= ( pad_count + fake_pad_count < 512 ); /* Always 1 */
#if defined(POLARSSL_SSL_DEBUG_ALL) #if defined(POLARSSL_SSL_DEBUG_ALL)
if( padlen > 0 && correct == 0) if( padlen > 0 && correct == 0)