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Message-ID: <511a3b91.ba09.181907e28b1.Coremail.duoming@zju.edu.cn>
Date: Thu, 23 Jun 2022 20:16:36 +0800 (GMT+08:00)
From: duoming@....edu.cn
To: "Paolo Abeni" <pabeni@...hat.com>
Cc: linux-hams@...r.kernel.org, ralf@...ux-mips.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 2/2] net: rose: fix null-ptr-deref caused by
rose_kill_by_neigh
Hello,
On Thu, 23 Jun 2022 11:30:04 +0200 Paolo Abeni 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)
> >
> > The rose->neighbour is set to null in position (1) and dereferenced
> > in position (2).
> >
> > The KASAN report triggered by POC is shown below:
> >
> > KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> > ...
> > RIP: 0010:rose_connect+0x6c2/0xf30
> > RSP: 0018:ffff88800ab47d60 EFLAGS: 00000206
> > RAX: 0000000000000005 RBX: 000000000000002a RCX: 0000000000000000
> > RDX: ffff88800ab38000 RSI: ffff88800ab47e48 RDI: ffff88800ab38309
> > RBP: dffffc0000000000 R08: 0000000000000000 R09: ffffed1001567062
> > R10: dfffe91001567063 R11: 1ffff11001567061 R12: 1ffff11000d17cd0
> > R13: ffff8880068be680 R14: 0000000000000002 R15: 1ffff11000d17cd0
> > ...
> > Call Trace:
> > <TASK>
> > ? __local_bh_enable_ip+0x54/0x80
> > ? selinux_netlbl_socket_connect+0x26/0x30
> > ? rose_bind+0x5b0/0x5b0
> > __sys_connect+0x216/0x280
> > __x64_sys_connect+0x71/0x80
> > do_syscall_64+0x43/0x90
> > entry_SYSCALL_64_after_hwframe+0x46/0xb0
> >
> > This patch adds lock_sock() in rose_kill_by_neigh() in order to
> > synchronize with rose_connect() and rose_release().
> >
> > Meanwhile, this patch adds sock_hold() protected by rose_list_lock
> > that could synchronize with rose_remove_socket() in order to mitigate
> > UAF bug caused by lock_sock() we add.
> >
> > What's more, there is no need using rose_neigh_list_lock to protect
> > rose_kill_by_neigh(). Because we have already used rose_neigh_list_lock
> > to protect the state change of rose_neigh in rose_link_failed(), which
> > is well synchronized.
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> > net/rose/af_rose.c | 5 +++++
> > net/rose/rose_route.c | 2 ++
> > 2 files changed, 7 insertions(+)
> >
> > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
> > index bf2d986a6bc..dece637e274 100644
> > --- a/net/rose/af_rose.c
> > +++ b/net/rose/af_rose.c
> > @@ -169,9 +169,14 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
> > struct rose_sock *rose = rose_sk(s);
> >
> > if (rose->neighbour == neigh) {
> > + sock_hold(s);
> > rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> > rose->neighbour->use--;
> > + spin_unlock_bh(&rose_list_lock);
>
> You can't release the lock protecting the list traversal, then re-
> acquire it and keep traversing using the same iterator. The list could
> be modified in-between.
I think release the lock and then reacquire it is ok. Because we have held the
refcount of sock and called rose_disconnect() to change the state of sock with
the protection of rose_list_lock which could synchronize with rose_destroy_socket().
If the sock is removed from the list by rose_destroy_socket(), there is
no rose->neighbour equals to neigh and the rose_kill_by_neigh() will return.
If there is a rose->neighbour equals to neigh, we held the refcount of sock
and called the rose_disconnect() to change the state of it with the protection
of rose_list_lock. Even if the sock could be removed from the rose_list by
rose_destroy_socket() during the time of unlocking, but the sock will not be
deallocated because we have held the refcount of sock. When we reacquire the
rose_list_lock, we only do sock_put() in order to deallocate the sock.
@@ -169,9 +169,15 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
struct rose_sock *rose = rose_sk(s);
if (rose->neighbour == neigh) {
+ sock_hold(s);
rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
rose->neighbour->use--;
+ spin_unlock_bh(&rose_list_lock);
+ lock_sock(s);
rose->neighbour = NULL;
+ release_sock(s);
+ spin_lock_bh(&rose_list_lock);
+ sock_put(s);
}
}
spin_unlock_bh(&rose_list_lock);
> Instead you could build a local list containing the relevant sockets
> (under the rose_list_lock protection), additionally acquiring a
> reference to each of them
>
> Then traverse such list outside the rose_list_lock, acquire the socket
> lock on each of them, do the neigh clearing and release the reference.
If we build a local list contain the relevant sockets and only acquire a reference
to each of them with the protection of rose_list_lock, the socket could be removed
by rose_destroy_socket() after we release the rose_list_lock. Then if we traverse
such list outside the rose_list_lock we could not find the socket, as a result,
the neigh clearing and the refcount releasing operations will not be executed.
Best regards,
Duoming Zhou
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