netdev - Re: [PATCH net] udp: on peeking bad csum, drop packets even if not at head

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Date:   Mon, 21 Aug 2017 21:11:13 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] udp: on peeking bad csum, drop packets even if not at head

On Mon, Aug 21, 2017 at 8:12 PM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> On Mon, Aug 21, 2017 at 6:40 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Mon, 2017-08-21 at 17:39 -0400, Willem de Bruijn wrote:
>>> From: Willem de Bruijn <willemb@...gle.com>
>>>
>>> When peeking, if a bad csum is discovered, the skb is unlinked from
>>> the queue with __sk_queue_drop_skb and the peek operation restarted.
>>>
>>> __sk_queue_drop_skb only drops packets that match the queue head. With
>>> sk_peek_off, the skb need not be at head, causing the call to fail and
>>> the same skb to be found again on restart.
>>>
>>> Walk the queue to find the correct skb. Limit the walk to sk_peek_off,
>>> to bound cycle cost to at most twice the original skb_queue_walk in
>>> __skb_try_recv_from_queue.
>>>
>>> The operation may race with updates to sk_peek_off. As the operation
>>> is retried, it will eventually succeed.
>>>
>>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>>
>> You forgot the Fixes: tag, that such a bug fix deserves.
>
> Indeed, sorry. I'm looking into that now. It should be the patch that
> introduced peeking at offset, but need to verify.

It is. Fixes: 627d2d6b5500 ("udp: enable MSG_PEEK at non-zero offset")