re: RDMA/rxe: Fix skb lifetime in rxe_rcv_mcast_pkt()

[Colin Ian King]

Hi,

Static analysis with Coverity has detected a potential issue with the
following commit:

commit e7ec96fc7932f48a6d6cdd05bf82004a1a04285b
Author: Bob Pearson <rpearsonhpe@xxxxxxxxx>
Date:   Thu Oct 8 15:36:52 2020 -0500

    RDMA/rxe: Fix skb lifetime in rxe_rcv_mcast_pkt()

The analysis is as follows:

   16. Condition mce->qp_list.next != &mcg->qp_list, taking true branch.

269                if (mce->qp_list.next != &mcg->qp_list)

   17. returned_null: skb_clone returns NULL (checked 153 out of 178 times).
   18. var_assigned: Assigning: per_qp_skb = NULL return value from
skb_clone.
   19. Falling through to end of if statement.
270                        per_qp_skb = skb_clone(skb, GFP_ATOMIC);
271                else
272                        per_qp_skb = skb;
273
274                per_qp_pkt = SKB_TO_PKT(per_qp_skb);
275                per_qp_pkt->qp = qp;
276                rxe_add_ref(qp);

Dereference null return value (NULL_RETURNS)
    20. dereference: Dereferencing a pointer that might be NULL
per_qp_skb when calling rxe_rcv_pkt.
277                rxe_rcv_pkt(per_qp_pkt, per_qp_skb);
278        }
279

It is possible for skb_clone to return NULL, so dereferencing the NULL
return pointer per_qp_skb is a potential issue.

Colin