From: Duoming Zhou <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, Duoming Zhou <duoming@zju.edu.cn>
Subject: [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect
Date: Sat, 26 Mar 2022 14:59:12 +0800 [thread overview]
Message-ID: <20220326065912.41077-1-duoming@zju.edu.cn> (raw)
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
next reply other threads:[~2022-03-26 6:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-26 6:59 Duoming Zhou [this message]
2022-03-26 7:14 ` [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect 周多明
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