From: Eric Dumazet <edumazet@google.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
David Miller <davem@davemloft.net>,
netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
syzkaller <syzkaller@googlegroups.com>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
James Morris <jmorris@namei.org>
Subject: Re: net: use-after-free in neigh_timer_handler/sock_wfree
Date: Wed, 1 Mar 2017 13:54:26 -0800 [thread overview]
Message-ID: <CANn89iJyDtZxj0Qksi7P7-FpEW4MDP6HpJTcb9o_yRXJQtym_g@mail.gmail.com> (raw)
In-Reply-To: <CAM_iQpUdpjXS-yq8McZne+hobWv+pQS-Q0Fk4w0i0mXJQQ8fhQ@mail.gmail.com>
On Wed, Mar 1, 2017 at 1:43 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>
>> This one looks very similar to a previous one:
>> https://groups.google.com/forum/#!topic/syzkaller/BhyN5OFd7sQ
>>
>> Both happen on raw v6 sockets.
>>
>> For me, it seems the sk refcnt is not correct, skb should still hold
>> a refcnt so it should not be freed before kfree_skb() in a timer
>> handler...
>
> More precisely, after this commit:
>
> commit 2b85a34e911bf483c27cfdd124aeb1605145dc80
> Author: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu Jun 11 02:55:43 2009 -0700
>
> net: No more expensive sock_hold()/sock_put() on each tx
>
> we don't take (old) refcnt any more on TX path, sk_wmem_alloc
> is the new refcnt. ;)
So the bug is that skb->truesize is mangled by reassembly unit,
while sbk->sk is tracking sk_wmem_alloc changes in order
to decide when it is safe to free sk.
This is why we need to call skb_orphan(), as we did for IPv4 in
8282f27449bf15548
next prev parent reply other threads:[~2017-03-01 23:00 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-01 19:27 net: use-after-free in neigh_timer_handler/sock_wfree Dmitry Vyukov
2017-03-01 21:24 ` Cong Wang
2017-03-01 21:43 ` Cong Wang
2017-03-01 21:54 ` Eric Dumazet [this message]
2017-03-01 23:09 ` Cong Wang
2017-03-01 23:15 ` Eric Dumazet
2017-03-02 5:25 ` Cong Wang
2017-03-02 5:36 ` Eric Dumazet
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