From: duoming@zju.edu.cn
To: linux-hams@vger.kernel.org, pabeni@redhat.com
Cc: ralf@linux-mips.org, davem@davemloft.net, edumazet@google.com,
kuba@kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net v5] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh
Date: Sun, 10 Jul 2022 21:52:06 +0800 (GMT+08:00) [thread overview]
Message-ID: <56319300.38660.181e861b71b.Coremail.duoming@zju.edu.cn> (raw)
Hello,
On Tue, 05 Jul 2022 10:43:44 +0200 pabeni@redhat.com wrote:
> On Sat, 2022-07-02 at 15:57 +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)
> >
> > 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@zju.edu.cn>
> > ---
> > Changes in v5:
> > - v5: Use socket lock to protect comparison in rose_kill_by_neigh.
> >
> > net/rose/af_rose.c | 12 ++++++++++++
> > net/rose/rose_route.c | 2 ++
> > 2 files changed, 14 insertions(+)
> >
> > 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--;
I am sorry for the delay.
> Note that the code can held different socket lock while updating
> 'neighbour->use'. That really means that such updates can really race
> each other, with bad results.
Thank you for your time and suggestions! I agree with you and I will improve
this patch.
> I think the only safe way out is using an atomic_t for 'neighbour->use'
> (likely a refcount_t would be a better option).
I will use refcount_t to manage the 'neighbour->use'.
> All the above deserves a separate patch IMHO.
>
> > rose->neighbour = NULL;
> > + release_sock(s);
> > + sock_put(s);
> > + spin_lock_bh(&rose_list_lock);
> > + goto again;
>
> This chunk is dup of the following lines, it could be dropped...
>
> > }
> > + release_sock(s);
> > + sock_put(s);
> > + spin_lock_bh(&rose_list_lock);
> > + goto again;
>
> ... if this would be correct, which apparently is not.
>
> What happens when 'rose->neighbour' is different from 'neigh' for first
> socket in rose_list?
I understand. If the 'rose->neighbour' is different from 'neigh' for the first socket
in the rose_list, the code will goto again and re-search the list. This will cause
infinite loop. I will improve this.
Best regards,
Duoming Zhou
next reply other threads:[~2022-07-10 13:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-10 13:52 duoming [this message]
2022-07-11 17:49 ` [PATCH net v5] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh Jakub Kicinski
2022-07-12 0:08 ` duoming
-- strict thread matches above, loose matches on Subject: below --
2022-07-02 7:57 Duoming Zhou
2022-07-05 8:43 ` Paolo Abeni
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