libgtp: Remove packets in tx queue belonging pdp being freed

Doing so should avoid the crash seen in OS#3956, where a message is
received in osmo-sgsn gtp iface after having received a DeleteCtxAccept
message where pdp and associated cbp is freed. As a result, when new
confirmation arrives, it can still be matched against an old request and
be sent to upper layers providing an already freed cbp.

With this patch, since all queued messages belonging to that pdp are
dropped, confirmation won't find a match and be discarded in libgtp.

In order to be able to drop all req messages belonging to a pdp, a new list
is added to pdp_t and qmsg_t are added to that list when inserted into the per-gsn
req transmit queue. This way upon pdp free time it's simply a
matter of iterating over that list to remove all messages.

There's no need to do same for resp queue, and it'd be actually
counter-productive, because it wouldn't be possible to detect and
discard duplicates anymore after pdp ctx has been freed.

Related: OS#3956
Change-Id: Id86d0b241454d3ad49c64c28087fd2710fa2d17a

1 files changed, 5 insertions, 0 deletions

diff --git a/gtp/gtp.c b/gtp/gtp.c
index 94c3245..799f8a7 100644
--- a/gtp/gtp.c
+++ b/gtp/gtp.c
@@ -513,6 +513,8 @@ static int gtp_req(struct gsn_t *gsn, uint8_t version, struct pdp_t *pdp,
 		qmsg->cbp = cbp;
 		qmsg->type = ntoh8(packet->gtp0.h.type);
 		qmsg->fd = fd;
+		if (pdp) /* echo requests are not pdp-bound */
+			llist_add(&qmsg->entry, &pdp->qmsg_list_req);
 	}
 	gsn->seq_next++;	/* Count up this time */
 	return 0;
@@ -697,6 +699,9 @@ static int gtp_resp(uint8_t version, struct gsn_t *gsn, struct pdp_t *pdp,
 		qmsg->cbp = NULL;
 		qmsg->type = 0;
 		qmsg->fd = fd;
+		/* No need to add to pdp list here, because even on pdp ctx free
+		   we want to leave messages in queue_resp until timeout to
+		   detect duplicates */
 	}
 	return 0;
 }