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

TODO-RELEASE

@@ -7,3 +7,5 @@
 # If any interfaces have been added since the last public release: c:r:a + 1.
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what		description / commit summary line
+libgtp		queue.h		struct qmsg_t got a new field: entry
+libgtp		pdp.h		struct pdp_t got a new field: qmsg_list_req

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;
 }

gtp/pdp.c

@@ -31,6 +31,7 @@
 #include "pdp.h"
 #include "gtp.h"
 #include "lookupa.h"
+#include "queue.h"
 
 /* ***********************************************************
  * Functions related to PDP storage
@@ -156,7 +157,7 @@ int gtp_pdp_newpdp(struct gsn_t *gsn, struct pdp_t **pdp, uint64_t imsi, uint8_t
 			}
 			/* Default: Generate G-PDU sequence numbers on Tx */
 			(*pdp)->tx_gpdu_seq = true;
-
+			INIT_LLIST_HEAD(&(*pdp)->qmsg_list_req);
 			return 0;
 		}
 	}
@@ -165,7 +166,17 @@ int gtp_pdp_newpdp(struct gsn_t *gsn, struct pdp_t **pdp, uint64_t imsi, uint8_t
 
 int pdp_freepdp(struct pdp_t *pdp)
 {
+	struct qmsg_t *qmsg, *qmsg2;
 	struct pdp_t *pdpa = pdp->gsn->pdpa;
+	int rc;
+
+	/* Remove all enqueued messages belonging to this pdp from req tx transmit
+	   queue. queue_freemsg will call llist_del(). */
+	llist_for_each_entry_safe(qmsg, qmsg2, &pdp->qmsg_list_req, entry) {
+		if ((rc = queue_freemsg(pdp->gsn->queue_req, qmsg)))
+			LOGP(DLGTP, LOGL_ERROR,
+			     "Failed freeing qmsg from qmsg_list_req during pdp_freepdp()! %d\n", rc);
+	}
 
 	pdp_tiddel(pdp);
 

gtp/pdp.h

@@ -17,6 +17,7 @@
 #include <netinet/in.h>
 
 #include <osmocom/core/defs.h>
+#include <osmocom/core/linuxlist.h>
 
 struct gsn_t;
 
@@ -241,6 +242,8 @@ struct pdp_t {
 	struct gsn_t *gsn; /* Back pointer to GSN where this pdp ctx belongs to */
 
 	bool tx_gpdu_seq;		/* Transmit (true) or suppress G-PDU sequence numbers */
+
+	struct llist_head qmsg_list_req; /* list of req qmsg_t in retrans queue belonging this pdp ctx */
 };
 
 /* functions related to pdp_t management */

gtp/queue.c

@@ -172,6 +172,7 @@ int queue_newmsg(struct queue_t *queue, struct qmsg_t **qmsg,
 	} else {
 		*qmsg = &queue->qmsga[queue->next];
 		queue_seqset(queue, *qmsg, peer, seq);
+		INIT_LLIST_HEAD(&(*qmsg)->entry);
 		(*qmsg)->state = 1;	/* Space taken */
 		(*qmsg)->this = queue->next;
 		(*qmsg)->next = -1;	/* End of the queue */
@@ -206,6 +207,8 @@ int queue_freemsg(struct queue_t *queue, struct qmsg_t *qmsg)
 		return EOF;	/* Not in queue */
 	}
 
+	llist_del(&qmsg->entry);
+
 	queue_seqdel(queue, qmsg);
 
 	if (qmsg->next == -1)	/* Are we the last in queue? */

gtp/queue.h

@@ -17,6 +17,8 @@
 #ifndef _QUEUE_H
 #define _QUEUE_H
 
+#include <osmocom/core/linuxlist.h>
+
 #include "gtp.h"
 
 #define QUEUE_DEBUG 0		/* Print debug information */
@@ -39,6 +41,7 @@ struct qmsg_t {			/* Holder for queued packets */
 	int this;		/* Pointer to myself */
 	time_t timeout;		/* When do we retransmit this packet? */
 	int retrans;		/* How many times did we retransmit this? */
+	struct llist_head entry; /* Listed with other qmsg_t belonging to a pdp_t->qmsg_list_req */
 };
 
 struct queue_t {