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Groups > linux.kernel > #1590845

Re: net: use-after-free in neigh_timer_handler/sock_wfree

From Cong Wang <xiyou.wangcong@gmail.com>
Newsgroups linux.kernel
Subject Re: net: use-after-free in neigh_timer_handler/sock_wfree
Date 2017-03-02 06:30 +0100
Message-ID <tgrtn-612-3@gated-at.bofh.it> (permalink)
References (1 earlier) <tgk8y-ze-17@gated-at.bofh.it> <tgkie-DA-11@gated-at.bofh.it> <tglxE-1Kg-9@gated-at.bofh.it> <tglHk-1Og-13@gated-at.bofh.it> <tglQZ-1Rz-7@gated-at.bofh.it>
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On Wed, Mar 1, 2017 at 3:15 PM, Eric Dumazet <edumazet@google.com> wrote:
> On Wed, Mar 1, 2017 at 3:09 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
>>
>> But I doubt skb_orphan() is the solution here, shouldn't we just
>> update sk->sk_wmem_alloc with skb->truesize changes?
>
> Is it worth it ? Apart from syszkaller I mean...
>
> We started with something that had a real impact on real workloads.
>
> 158f323b9868b59967ad96957c4ca388161be321 net: adjust skb->truesize in
> pskb_expand_head()
>
> Note that auditing the stack took me a while.

I don't know how sk refcnt could work correctly without making
sk_wmem_alloc correctly. We certainly could just call skb_orphan()
is we don't need skb->sk any more, probably like the frag case,
but for this case, the neigh one, the skb's sitting in neigh->arp_queue
are not going to be freed unless in failed case, therefore skb->sk
should not be orphaned so early.

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Thread

Re: net: use-after-free in neigh_timer_handler/sock_wfree Cong Wang <xiyou.wangcong@gmail.com> - 2017-03-01 22:40 +0100
  Re: net: use-after-free in neigh_timer_handler/sock_wfree Cong Wang <xiyou.wangcong@gmail.com> - 2017-03-01 22:50 +0100
    Re: net: use-after-free in neigh_timer_handler/sock_wfree Eric Dumazet <edumazet@google.com> - 2017-03-02 00:10 +0100
      Re: net: use-after-free in neigh_timer_handler/sock_wfree Cong Wang <xiyou.wangcong@gmail.com> - 2017-03-02 00:20 +0100
        Re: net: use-after-free in neigh_timer_handler/sock_wfree Eric Dumazet <edumazet@google.com> - 2017-03-02 00:30 +0100
          Re: net: use-after-free in neigh_timer_handler/sock_wfree Cong Wang <xiyou.wangcong@gmail.com> - 2017-03-02 06:30 +0100
            Re: net: use-after-free in neigh_timer_handler/sock_wfree Eric Dumazet <edumazet@google.com> - 2017-03-02 06:50 +0100

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