RDMA/rxe: Fix seg fault in rxe_comp_queue_pkt

JIRA: https://issues.redhat.com/browse/RHEL-44248
CVE: CVE-2024-38544

commit 2b23b60
Author: Bob Pearson <rpearsonhpe@gmail.com>
Date:   Fri Mar 29 09:55:04 2024 -0500

    RDMA/rxe: Fix seg fault in rxe_comp_queue_pkt

    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>

Signed-off-by: Kamal Heib <kheib@redhat.com>

Author: Kamalheib

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