From: duoming@zju.edu.cn
To: Jakub Kicinski <kuba@kernel.org>
Cc: linux-hams@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, ralf@linux-mips.org,
davem@davemloft.net, edumazet@google.com, pabeni@redhat.com
Subject: Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh
Date: Sun, 3 Jul 2022 08:43:10 +0800 (GMT+08:00) [thread overview]
Message-ID: <194120ff.22ed2.181c182e706.Coremail.duoming@zju.edu.cn> (raw)
In-Reply-To: <20220702120108.32985427@kernel.org>
Hello,
On Sat, 2 Jul 2022 12:01:08 -0700 Jakub Kicinski wrote:
> On Sat, 2 Jul 2022 15:23:57 +0800 (GMT+08:00) duoming@zju.edu.cn wrote:
> > > On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:
> > > > When the link layer connection is broken, the rose->neighbour is
> > > > set to null. But rose->neighbour could be used by rose_connection()
> > > > and rose_release() later, because there is no synchronization among
> > > > them. As a result, the null-ptr-deref bugs will happen.
> > > >
> > > > One of the null-ptr-deref bugs is shown below:
> > > >
> > > > (thread 1) | (thread 2)
> > > > | rose_connect
> > > > rose_kill_by_neigh | lock_sock(sk)
> > > > spin_lock_bh(&rose_list_lock) | if (!rose->neighbour)
> > > > rose->neighbour = NULL;//(1) |
> > > > | rose->neighbour->use++;//(2)
> > >
> > > > if (rose->neighbour == neigh) {
> > >
> > > Why is it okay to perform this comparison without the socket lock,
> > > if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
> > > is not guaranteed to clear all the uses of a neighbor.
> >
> > I am sorry, the comparision should also be protected with socket lock.
> > The rose_kill_by_neigh() only clear the neighbor that is passed as
> > parameter of rose_kill_by_neigh().
>
> Don't think that's possible, you'd have to drop the neigh lock every
> time.
The neighbour is cleared in two situations.
(1) When the rose device is down, the rose_link_device_down() traverses
the rose_neigh_list and uses the rose_kill_by_neigh() to clear the
neighbors of the device.
void rose_link_device_down(struct net_device *dev)
{
struct rose_neigh *rose_neigh;
for (rose_neigh = rose_neigh_list; rose_neigh != NULL; rose_neigh = rose_neigh->next) {
if (rose_neigh->dev == dev) {
rose_del_route_by_neigh(rose_neigh);
rose_kill_by_neigh(rose_neigh);
}
}
}
https://elixir.bootlin.com/linux/v5.19-rc4/source/net/rose/rose_route.c#L839
(2) When the level 2 link has timed out, the rose_link_failed() calls rose_kill_by_neigh()
to clear the rose_neigh.
https://elixir.bootlin.com/linux/v5.19-rc4/source/net/rose/rose_route.c#L813
> > > > + sock_hold(s);
> > > > + spin_unlock_bh(&rose_list_lock);
> > > > + lock_sock(s);
> > > > rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> > > > rose->neighbour->use--;
> > >
> > > What protects the use counter?
> >
> > The use counter is protected by socket lock.
>
> Which one, the neigh object can be shared by multiple sockets, no?
The sk_for_each() traverses the rose_list and uses the lock of the socket that is extracted
from the rose_list to protect the use counter.
diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index bf2d986a6bc..6d5088b030a 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -165,14 +165,26 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
struct sock *s;
spin_lock_bh(&rose_list_lock);
+again:
sk_for_each(s, &rose_list) {
struct rose_sock *rose = rose_sk(s);
+ sock_hold(s);
+ spin_unlock_bh(&rose_list_lock);
+ lock_sock(s);
if (rose->neighbour == neigh) {
rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
rose->neighbour->use--;
rose->neighbour = NULL;
+ release_sock(s);
+ sock_put(s);
+ spin_lock_bh(&rose_list_lock);
+ goto again;
}
+ release_sock(s);
+ sock_put(s);
+ spin_lock_bh(&rose_list_lock);
+ goto again;
}
spin_unlock_bh(&rose_list_lock);
}
Best regards,
Duoming Zhou
prev parent reply other threads:[~2022-07-03 0:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-29 10:49 [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh Duoming Zhou
2022-07-02 2:41 ` Jakub Kicinski
2022-07-02 7:23 ` duoming
2022-07-02 19:01 ` Jakub Kicinski
2022-07-03 0:43 ` duoming [this message]
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