netdev - Re: [PATCH net-next] tcp: fix tcp_send_syn

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Date:   Wed, 18 Oct 2017 14:40:02 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix tcp_send_syn_data()

On Wed, Oct 18, 2017 at 2:20 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> syn_data was allocated by sk_stream_alloc_skb(), meaning
> its destructor and _skb_refdst fields are mangled.
>
> We need to call tcp_skb_tsorted_anchor_cleanup() before
> calling kfree_skb() or kernel crashes.
>
> Bug was reported by syzkaller bot.
>
> Fixes: e2080072ed2d ("tcp: new list for sent but unacked skbs for RACK recovery")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>

Thanks for the fix!
> ---
>  net/ipv4/tcp_output.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 53dc1267c85e668d9a6d5d60d24e6101f7a9c56b..988733f289c8c43f3ed88a9ae1b7f272ab8de1a2 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3383,6 +3383,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
>                 int copied = copy_from_iter(skb_put(syn_data, space), space,
>                                             &fo->data->msg_iter);
>                 if (unlikely(!copied)) {
> +                       tcp_skb_tsorted_anchor_cleanup(syn_data);
>                         kfree_skb(syn_data);
>                         goto fallback;
>                 }
>
>