RDMA/rxe: Fix seg fault in rxe_comp_queue_pkt

jira LE-1907
cve CVE-2024-38544
Rebuild_History Non-Buildable kernel-5.14.0-427.33.1.el9_4
commit-author Bob Pearson <rpearsonhpe@gmail.com>
commit 2b23b60

In rxe_comp_queue_pkt() an incoming response packet skb is enqueued to the
resp_pkts queue and then a decision is made whether to run the completer
task inline or schedule it. Finally the skb is dereferenced to bump a 'hw'
performance counter. This is wrong because if the completer task is
already running in a separate thread it may have already processed the skb
and freed it which can cause a seg fault.  This has been observed
infrequently in testing at high scale.

This patch fixes this by changing the order of enqueuing the packet until
after the counter is accessed.

Link: https://lore.kernel.org/r/20240329145513.35381-4-rpearsonhpe@gmail.com
	Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Fixes: 0b1e5b9 ("IB/rxe: Add port protocol stats")
	Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
(cherry picked from commit 2b23b60)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

drivers/infiniband/sw/rxe/rxe_comp.c

@@ -131,12 +131,12 @@ void rxe_comp_queue_pkt(struct rxe_qp *qp, struct sk_buff *skb)
 {
 	int must_sched;
 
-	skb_queue_tail(&qp->resp_pkts, skb);
-
-	must_sched = skb_queue_len(&qp->resp_pkts) > 1;
+	must_sched = skb_queue_len(&qp->resp_pkts) > 0;
 	if (must_sched != 0)
 		rxe_counter_inc(SKB_TO_PKT(skb)->rxe, RXE_CNT_COMPLETER_SCHED);
 
+	skb_queue_tail(&qp->resp_pkts, skb);
+
 	if (must_sched)
 		rxe_sched_task(&qp->comp.task);
 	else