netdev - Re: [PATCH net] sock: correct sk_wmem_queued accounting on efault in tcp zerocopy

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Date:   Thu, 19 Oct 2017 09:45:14 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] sock: correct sk_wmem_queued accounting on efault in
 tcp zerocopy

On Thu, Oct 19, 2017 at 9:40 AM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> From: Willem de Bruijn <willemb@...gle.com>
>
> Syzkaller hits WARN_ON(sk->sk_wmem_queued) in sk_stream_kill_queues
> after triggering an EFAULT in __zerocopy_sg_from_iter.
>
> On this error, skb_zerocopy_stream_iter resets the skb to its state
> before the operation with __pskb_trim. It cannot kfree_skb like
> datagram callers, as the skb may have data from a previous send call.
>
> __pskb_trim calls skb_condense for unowned skbs, which adjusts their
> truesize. These tcp skbuffs are owned and their truesize must add up
> to sk_wmem_queued. But they match because their skb->sk is NULL until
> tcp_transmit_skb.
>
> Temporarily set skb->sk when calling __pskb_trim to signal that the
> skbuffs are owned and avoid the skb_condense path.
>
> Fixes: 52267790ef52 ("sock: add MSG_ZEROCOPY")
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks a lot Willem.