1 files changed, 38 insertions, 38 deletions

diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index 9246ff2951..b2e5dc1882 100644
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -290,11 +290,9 @@ static int ssl3_get_record(SSL *s)
 	unsigned char *p;
 	unsigned char md[EVP_MAX_MD_SIZE];
 	short version;
-	int mac_size;
+	unsigned mac_size;
 	int clear=0;
 	size_t extra;
-	int decryption_failed_or_bad_record_mac = 0;
-	unsigned char *mac = NULL;
 
 	rr= &(s->s3->rrec);
 	sess=s->session;
@@ -405,17 +403,10 @@ fprintf(stderr, "Record type=%d, Length=%d\n", rr->type, rr->length);
 	rr->data=rr->input;
 
 	enc_err = s->method->ssl3_enc->enc(s,0);
-	if (enc_err <= 0)
+	if (enc_err == 0)
 		{
-		if (enc_err == 0)
-			/* SSLerr() and ssl3_send_alert() have been called */
-			goto err;
-
-		/* Otherwise enc_err == -1, which indicates bad padding
-		 * (rec->length has not been changed in this case).
-		 * To minimize information leaked via timing, we will perform
-		 * the MAC computation anyway. */
-		decryption_failed_or_bad_record_mac = 1;
+		/* SSLerr() and ssl3_send_alert() have been called */
+		goto err;
 		}
 
 #ifdef TLS_DEBUG
@@ -433,45 +424,54 @@ printf("\n");
 	if (!clear)
 		{
 		/* !clear => s->read_hash != NULL => mac_size != -1 */
+		unsigned char *mac = NULL;
+		unsigned char mac_tmp[EVP_MAX_MD_SIZE];
 		mac_size=EVP_MD_CTX_size(s->read_hash);
-		OPENSSL_assert(mac_size >= 0);
+		OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);
 
-		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+		/* orig_len is the length of the record before any padding was
+		 * removed. This is public information, as is the MAC in use,
+		 * therefore we can safely process the record in a different
+		 * amount of time if it's too short to possibly contain a MAC.
+		 */
+		if (rr->orig_len < mac_size ||
+		    /* CBC records must have a padding length byte too. */
+		    (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+		     rr->orig_len < mac_size+1))
 			{
-#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
-			al=SSL_AD_RECORD_OVERFLOW;
-			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_PRE_MAC_LENGTH_TOO_LONG);
+			al=SSL_AD_DECODE_ERROR;
+			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
 			goto f_err;
-#else
-			decryption_failed_or_bad_record_mac = 1;
-#endif			
 			}
-		/* check the MAC for rr->input (it's in mac_size bytes at the tail) */
-		if (rr->length >= (unsigned int)mac_size)
+
+		if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE)
 			{
+			/* We update the length so that the TLS header bytes
+			 * can be constructed correctly but we need to extract
+			 * the MAC in constant time from within the record,
+			 * without leaking the contents of the padding bytes.
+			 * */
+			mac = mac_tmp;
+			ssl3_cbc_copy_mac(mac_tmp, rr, mac_size);
 			rr->length -= mac_size;
-			mac = &rr->data[rr->length];
 			}
 		else
 			{
-			/* record (minus padding) is too short to contain a MAC */
-#if 0 /* OK only for stream ciphers */
-			al=SSL_AD_DECODE_ERROR;
-			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
-			goto f_err;
-#else
-			decryption_failed_or_bad_record_mac = 1;
-			rr->length = 0;
-#endif
+			/* In this case there's no padding, so |rec->orig_len|
+			 * equals |rec->length| and we checked that there's
+			 * enough bytes for |mac_size| above. */
+			rr->length -= mac_size;
+			mac = &rr->data[rr->length];
 			}
-		i=s->method->ssl3_enc->mac(s,md,0);
+
+		i=s->method->ssl3_enc->mac(s,md,0 /* not send */);
 		if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
-			{
-			decryption_failed_or_bad_record_mac = 1;
-			}
+			enc_err = -1;
+		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+			enc_err = -1;
 		}
 
-	if (decryption_failed_or_bad_record_mac)
+	if (enc_err < 0)
 		{
 		/* A separate 'decryption_failed' alert was introduced with TLS 1.0,
 		 * SSL 3.0 only has 'bad_record_mac'.  But unless a decryption