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

[Bob Pearson <rpearsonhpe@gmail.com>]

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.