res_pjsip: Prevent access of NULL channels.

It is possible to receive incoming requests or responses after the channel
on an ast_sip_session has been destroyed and NULLed out. Handlers of these
sorts of requests or responses need to be prepared for the possibility
that the channel is NULL or else they could cause a crash.

While several places have been amended to deal with NULL channels, there
were still a couple of places that needed updating.

res_pjsip_dtmf_info.c: When handling incoming INFO requests, we need to
return early if there is no channel on the session.

res_pjsip_session.c: When handling a 302 response, we need to stop the
redirecting attempt if there is no channel on the session.

ASTERISK-25148 #close
reported by Mark Michelson

Change-Id: Id1a75ffc3d0eaa168b0b28188fb54d6cf9fc47a9

1 files changed, 7 insertions, 1 deletions

diff --git a/res/res_pjsip_dtmf_info.c b/res/res_pjsip_dtmf_info.c
index b0a6649a0..7b52250c8 100644
--- a/res/res_pjsip_dtmf_info.c
+++ b/res/res_pjsip_dtmf_info.c
@@ -89,7 +89,13 @@ static int dtmf_info_incoming_request(struct ast_sip_session *session, struct pj
 	char event = '\0';
 	unsigned int duration = 100;
 
-	char is_dtmf = is_media_type(rdata, "dtmf");
+	char is_dtmf;
+
+	if (!session->channel) {
+		return 0;
+	}
+
+	is_dtmf = is_media_type(rdata, "dtmf");
 
 	if (!is_dtmf && !is_media_type(rdata, "dtmf-relay")) {
 		return 0;