Re: [PATCH for-next] RDMA/rxe: Fix coding error in rxe_rcv_mcast_pkt

[Bob Pearson <rpearsonhpe@gmail.com>]

On 1/27/21 9:53 PM, Bob Pearson wrote:
> On 1/27/21 9:50 PM, Zhu Yanjun wrote:
>> On Thu, Jan 28, 2021 at 9:12 AM Bob Pearson <rpearsonhpe@gmail.com> wrote:
>>>
>>> rxe_rcv_mcast_pkt() in rxe_recv.c can leak SKBs in error path
>>> code. The loop over the QPs attached to a multicast group
>>> creates new cloned SKBs for all but the last QP in the list
>>> and passes the SKB and its clones to rxe_rcv_pkt() for further
>>> processing. Any QPs that do not pass some checks are skipped.
>>> If the last QP in the list fails the tests the SKB is leaked.
>>> This patch checks if the SKB for the last QP was used and if
>>> not frees it. Also removes a redundant loop invariant assignment.
>>>
>>> Fixes: 8700e3e7c4857 ("Soft RoCE driver")
>>> Fixes: 71abf20b28ff8 ("RDMA/rxe: Handle skb_clone() failure in rxe_recv.c")
>>> Signed-off-by: Bob Pearson <rpearson@hpe.com>
>>> ---
>>>  drivers/infiniband/sw/rxe/rxe_recv.c | 18 +++++++++++-------
>>>  1 file changed, 11 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
>>> index c9984a28eecc..57cc25e3b4ad 100644
>>> --- a/drivers/infiniband/sw/rxe/rxe_recv.c
>>> +++ b/drivers/infiniband/sw/rxe/rxe_recv.c
>>> @@ -252,7 +252,6 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
>>>
>>>         list_for_each_entry(mce, &mcg->qp_list, qp_list) {
>>>                 qp = mce->qp;
>>> -               pkt = SKB_TO_PKT(skb);
>>>
>>>                 /* validate qp for incoming packet */
>>>                 err = check_type_state(rxe, pkt, qp);
>>> @@ -264,12 +263,18 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
>>>                         continue;
>>>
>>>                 /* for all but the last qp create a new clone of the
>>> -                * skb and pass to the qp.
>>> +                * skb and pass to the qp. If an error occurs in the
>>> +                * checks for the last qp in the list we need to
>>> +                * free the skb since it hasn't been passed on to
>>> +                * rxe_rcv_pkt() which would free it later.
>>>                  */
>>> -               if (mce->qp_list.next != &mcg->qp_list)
>>> +               if (mce->qp_list.next != &mcg->qp_list) {
>>>                         per_qp_skb = skb_clone(skb, GFP_ATOMIC);
>>> -               else
>>> +               } else {
>>>                         per_qp_skb = skb;
>>> +                       /* show we have consumed the skb */
>>> +                       skb = NULL;
>>> +               }
>>>
>>>                 if (unlikely(!per_qp_skb))
>>>                         continue;
>>> @@ -284,10 +289,9 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
>>>
>>>         rxe_drop_ref(mcg);      /* drop ref from rxe_pool_get_key. */
>>>
>>> -       return;
>>> -
>>>  err1:
>>> -       kfree_skb(skb);
>>> +       if (skb)
>>> +               kfree_skb(skb);
>>
>> "if (skb)" is not needed here.
>>
>> The implemetation of kfree_skb:
>>
>> void kfree_skb(struct sk_buff *skb)
>> {
>> if (unlikely(!skb))
>> return;
>> if (likely(atomic_read(&skb->users) == 1))
>> smp_rmb();
>> else if (likely(!atomic_dec_and_test(&skb->users)))
>> return;
>> trace_kfree_skb(skb, __builtin_return_address(0));
>> __kfree_skb(skb);
>> }
>>
>> Zhu Yanjun
>>>  }
>>>
>>>  /**
>>> --
>>> 2.27.0
>>>
> Agreed but the reason I wrote that was to make it obvious why I set skb to NULL above. But as long as it is clear without it I can remove the test.
> 
Actually I should have written

if (unlikely(skb))
	kfree_skb(skb);