On Fri, Mar 3, 2017 at 7:01 PM, Eric Dumazet <eduma...@google.com> wrote:
> TX skbs do not necessarily hold a reference on skb->sk->sk_refcnt
> By the time TX completion happens, sk_refcnt might be already 0.
>
> sock_hold()/sock_put() would then corrupt critical state, like
> sk_wmem_alloc.
>
> Fixes: bf7fa551e0ce ("mac80211: Resolve sk_refcnt/sk_wmem_alloc issue in wifi
> ack path")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Cc: Alexander Duyck <alexander.h.du...@intel.com>
> Cc: Johannes Berg <johan...@sipsolutions.net>
> Cc: Soheil Hassas Yeganeh <soh...@google.com>
> Cc: Willem de Bruijn <will...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
> ---
> net/core/skbuff.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index
> f3557958e9bf147631a90b51fef0630920acd97b..e2f37a560ec43ccf60a71f190423bd265eccf594
> 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3893,7 +3893,7 @@ void skb_complete_wifi_ack(struct sk_buff *skb, bool
> acked)
> {
> struct sock *sk = skb->sk;
> struct sock_exterr_skb *serr;
> - int err;
> + int err = 1;
>
> skb->wifi_acked_valid = 1;
> skb->wifi_acked = acked;
> @@ -3903,14 +3903,15 @@ void skb_complete_wifi_ack(struct sk_buff *skb, bool
> acked)
> serr->ee.ee_errno = ENOMSG;
> serr->ee.ee_origin = SO_EE_ORIGIN_TXSTATUS;
>
> - /* take a reference to prevent skb_orphan() from freeing the socket */
> - sock_hold(sk);
> -
> - err = sock_queue_err_skb(sk, skb);
> + /* Take a reference to prevent skb_orphan() from freeing the socket,
> + * but only if the socket refcount is not zero.
> + */
> + if (likely(atomic_inc_not_zero(&sk->sk_refcnt))) {
> + err = sock_queue_err_skb(sk, skb);
> + sock_put(sk);
> + }
> if (err)
> kfree_skb(skb);
> -
> - sock_put(sk);
> }
> EXPORT_SYMBOL_GPL(skb_complete_wifi_ack);
>
> --
> 2.12.0.rc1.440.g5b76565f74-goog
>
Nice fix!
