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

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Message-Id: <20171022.015200.2223977227108729125.davem@davemloft.net>
Date:   Sun, 22 Oct 2017 01:52:00 +0100 (WEST)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, willemb@...gle.com
Subject: Re: [PATCH net] sock: correct sk_wmem_queued accounting on efault
 in tcp zerocopy

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Thu, 19 Oct 2017 12:40:39 -0400

> 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>

Applied.