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Date:   Fri, 3 Mar 2017 19:43:08 -1000
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Johannes Berg <johannes@...solutions.net>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net 2/2] net: fix socket refcounting in skb_complete_tx_timestamp()

On Fri, Mar 3, 2017 at 7:01 PM, Eric Dumazet <edumazet@...gle.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 and lead to leaks or use after free.
>
> Fixes: 62bccb8cdb69 ("net-timestamp: Make the clone operation stand-alone from phy timestamping")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Alexander Duyck <alexander.h.duyck@...el.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> Cc: Soheil Hassas Yeganeh <soheil@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.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 e2f37a560ec43ccf60a71f190423bd265eccf594..cd4ba8c6b6091651403cf74de8c60ccf69aa3e7b 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3828,13 +3828,14 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
>         if (!skb_may_tx_timestamp(sk, false))
>                 return;
>
> -       /* take a reference to prevent skb_orphan() from freeing the socket */
> -       sock_hold(sk);
> -
> -       *skb_hwtstamps(skb) = *hwtstamps;
> -       __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND);
> -
> -       sock_put(sk);
> +       /* 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))) {
> +               *skb_hwtstamps(skb) = *hwtstamps;
> +               __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND);
> +               sock_put(sk);
> +       }
>  }
>  EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
>
> --
> 2.12.0.rc1.440.g5b76565f74-goog
>

Thanks for the fix!

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