netdev - Re: [PATCH net] net: adjust skb->truesize in ___pskb

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Date:   Wed, 26 Apr 2017 19:08:40 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net: adjust skb->truesize in ___pskb_trim()

On Wed, Apr 26, 2017 at 6:07 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Andrey found a way to trigger the WARN_ON_ONCE(delta < len) in
> skb_try_coalesce() using syzkaller and a filter attached to a TCP
> socket.
>
> As we did recently in commit 158f323b9868 ("net: adjust skb->truesize in
> pskb_expand_head()") we can adjust skb->truesize from ___pskb_trim(),
> via a call to skb_condense().
>
> If all frags were freed, then skb->truesize can be recomputed.
>
> This call can be done if skb is not yet owned, or destructor is
> sock_edemux().

Hi Eric,

I still see the warning even with your patch.

Thanks!

>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/core/skbuff.c |    2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index f86bf69cfb8d8bc17262cdba5d9f57a4726cd476..f1d04592ace02f32efa6e05df89c9a5e0023157f 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1576,6 +1576,8 @@ int ___pskb_trim(struct sk_buff *skb, unsigned int len)
>                 skb_set_tail_pointer(skb, len);
>         }
>
> +       if (!skb->sk || skb->destructor == sock_edemux)
> +               skb_condense(skb);
>         return 0;
>  }
>  EXPORT_SYMBOL(___pskb_trim);
>
>