Commit 32cc2479 authored by Dr. Stephen Henson's avatar Dr. Stephen Henson
Browse files

Fix IV check and padding removal. 

Fix the calculation that checks there is enough room in a record
after removing padding and optional explicit IV. (by Steve)

For AEAD remove the correct number of padding bytes (by Andy)
parent f306b87d

ssl/s3_cbc.c

+12 −21
Original line number Diff line number Diff line
@@ -139,31 +139,22 @@ int tls1_cbc_remove_padding(const SSL* s, 
			    unsigned mac_size)

	{

	unsigned padding_length, good, to_check, i;

	const char has_explicit_iv =

		s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION;

	const unsigned overhead = 1 /* padding length byte */ +

				  mac_size +

				  (has_explicit_iv ? block_size : 0);



	/* These lengths are all public so we can test them in non-constant

	 * time. */

	if (overhead > rec->length)

		return 0;



	/* We can always safely skip the explicit IV. We check at the beginning

	 * of this function that the record has at least enough space for the

	 * IV, MAC and padding length byte. (These can be checked in

	 * non-constant time because it's all public information.) So, if the

	 * padding was invalid, then we didn't change |rec->length| and this is

	 * safe. If the padding was valid then we know that we have at least

	 * overhead+padding_length bytes of space and so this is still safe

	 * because overhead accounts for the explicit IV. */

	if (has_explicit_iv)

	const unsigned overhead = 1 /* padding length byte */ + mac_size;

	/* Check if version requires explicit IV */

	if (s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION)

		{

		/* These lengths are all public so we can test them in

		 * non-constant time.

		 */

		if (overhead + block_size > rec->length)

			return 0;

		/* We can now safely skip explicit IV */

		rec->data += block_size;

		rec->input += block_size;

		rec->length -= block_size;

		}

	else if (overhead > rec->length)

		return 0;



	padding_length = rec->data[rec->length-1];
@@ -190,7 +181,7 @@ int tls1_cbc_remove_padding(const SSL* s, 
	if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER)

		{

		/* padding is already verified */

		rec->length -= padding_length;

		rec->length -= padding_length + 1;

		return 1;

		}