Fix a mem leak in NPN handling

If a server sent multiple NPN extensions in a single ClientHello then a
mem leak can occur. This will only happen where the client has requested
NPN in the first place. It does not occur during renegotiation. Therefore
the maximum that could be leaked in a single connection with a malicious
server is 64k (the maximum size of the ServerHello extensions section). As
this is client side, only occurs if NPN has been requested and does not
occur during renegotiation this is unlikely to be exploitable.

Issue reported by Shi Lei.

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

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index d7ccea260d5f83495872376a48dd62560a7cec4c..4733bff3a35b746aecce992f57fb2be17e178563 100644 (file)
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2394,6 +2394,11 @@ static int ssl_scan_serverhello_tlsext(SSL *s, PACKET *pkt, int *al)
                 *al = TLS1_AD_INTERNAL_ERROR;
                 return 0;
             }
+            /*
+             * Could be non-NULL if server has sent multiple NPN extensions in
+             * a single Serverhello
+             */
+            OPENSSL_free(s->next_proto_negotiated);
             s->next_proto_negotiated = OPENSSL_malloc(selected_len);
             if (s->next_proto_negotiated == NULL) {
                 *al = TLS1_AD_INTERNAL_ERROR;