* [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect
@ 2022-03-26 6:59 Duoming Zhou
2022-03-26 7:14 ` 周多明
0 siblings, 1 reply; 2+ messages in thread
From: Duoming Zhou @ 2022-03-26 6:59 UTC (permalink / raw)
To: netdev
Cc: linux-x25, linux-kernel, ms, davem, kuba, pabeni, tanxin.ctf,
linma, xiyuyang19, Duoming Zhou
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net] net/x25: Fix null-ptr-deref caused by x25_disconnect
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
0 siblings, 0 replies; 2+ messages in thread
From: 周多明 @ 2022-03-26 7:14 UTC (permalink / raw)
To: netdev
Cc: linux-x25, linux-kernel, ms, davem, kuba, pabeni, tanxin.ctf,
linma, xiyuyang19
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
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