From: 周多明 <duoming@zju.edu.cn>
To: netdev@vger.kernel.org
Cc: linux-x25@vger.kernel.org, linux-kernel@vger.kernel.org,
ms@dev.tdt.de, davem@davemloft.net, kuba@kernel.org,
pabeni@redhat.com, tanxin.ctf@gmail.com, linma@zju.edu.cn,
xiyuyang19@fudan.edu.cn
Subject: Re: [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect
Date: Sat, 26 Mar 2022 15:14:55 +0800 (GMT+08:00) [thread overview]
Message-ID: <4569327b.1ae29.17fc513fb2f.Coremail.duoming@zju.edu.cn> (raw)
In-Reply-To: <20220326065912.41077-1-duoming@zju.edu.cn>
I am sorry, this patch has a problem. I will send the correct version later.
> The previous commit 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when
> x25 disconnect") adds decrement of refcount of x25->neighbour and sets
> x25->neighbour to NULL in x25_disconnect(), but when the link layer is
> terminating, it could cause null-ptr-deref bugs in x25_sendmsg(),
> x25_recvmsg() and x25_connect(). One of the bugs is shown below.
>
> x25_link_terminated() | x25_recvmsg()
> x25_kill_by_neigh() | ...
> x25_disconnect() | lock_sock(sk)
> ... | ...
> x25->neighbour = NULL //(1) |
> ... | x25->neighbour->extended //(2)
>
> We set NULL to x25->neighbour in position (1) and dereference
> x25->neighbour in position (2), which could cause null-ptr-deref bug.
>
> This patch adds lock_sock(sk) in x25_disconnect() in order to synchronize
> with x25_sendmsg(), x25_recvmsg() and x25_connect(). What`s more, the sk
> held by lock_sock() is not NULL, because it is extracted from x25_list
> and uses x25_list_lock to synchronize.
>
> Fixes: 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect")
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> ---
> net/x25/x25_subr.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/x25/x25_subr.c b/net/x25/x25_subr.c
> index 0285aaa1e93..4e19752bdd0 100644
> --- a/net/x25/x25_subr.c
> +++ b/net/x25/x25_subr.c
> @@ -360,7 +360,9 @@ void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
> if (x25->neighbour) {
> read_lock_bh(&x25_list_lock);
> x25_neigh_put(x25->neighbour);
> + lock_sock(sk);
> x25->neighbour = NULL;
> + release_sock(sk);
> read_unlock_bh(&x25_list_lock);
> }
> }
> --
> 2.17.1
prev parent reply other threads:[~2022-03-26 7:14 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-26 6:59 [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect Duoming Zhou
2022-03-26 7:14 ` 周多明 [this message]
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