Fix a hang with SSL_peek()

If while calling SSL_peek() we read an empty record then we go into an
infinite loop, continually trying to read data from the empty record and
never making any progress. This could be exploited by a malicious peer in
a Denial Of Service attack.

CVE-2016-6305

GitHub Issue #1563

Reviewed-by: Rich Salz <rsalz@openssl.org>

diff --git a/ssl/record/rec_layer_s3.c b/ssl/record/rec_layer_s3.c
index abde9d4a73447da0142ae4d4d04facfe55db79bc..0775095b9a317e30c94928258776d3fa12992dfd 100644 (file)
--- a/ssl/record/rec_layer_s3.c
+++ b/ssl/record/rec_layer_s3.c
@@ -1133,7 +1133,11 @@ int ssl3_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
 
             memcpy(buf, &(rr->data[rr->off]), n);
             buf += n;
-            if (!peek) {
+            if (peek) {
+                /* Mark any zero length record as consumed CVE-2016-6305 */
+                if (SSL3_RECORD_get_length(rr) == 0)
+                    SSL3_RECORD_set_read(rr);
+            } else {
                 SSL3_RECORD_sub_length(rr, n);
                 SSL3_RECORD_add_off(rr, n);
                 if (SSL3_RECORD_get_length(rr) == 0) {