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Date:   Tue, 13 Feb 2018 19:52:01 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Girish Moodalbail <girish.moodalbail@...cle.com>
Cc:     syzbot 
        <bot+643ecad3f5bb49700e839363b608c4928f6db8f0@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>, linux-rdma@...r.kernel.org,
        netdev <netdev@...r.kernel.org>, rds-devel@....oracle.com,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in rds_tcp_dev_event

On Tue, Nov 14, 2017 at 4:30 AM, Girish Moodalbail
<girish.moodalbail@...cle.com> wrote:
> On 11/7/17 12:28 PM, syzbot wrote:
>>
>> Hello,
>>
>> syzkaller hit the following crash on
>> 287683d027a3ff83feb6c7044430c79881664ecf
>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>> compiler: gcc (GCC) 7.1.1 20170620
>> .config is attached
>> Raw console output is attached.
>>
>>
>>
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in rds_tcp_kill_sock net/rds/tcp.c:530 [inline]
>> BUG: KASAN: use-after-free in rds_tcp_dev_event+0xc01/0xc90
>> net/rds/tcp.c:568
>> Read of size 8 at addr ffff8801cd879200 by task kworker/u4:3/147
>>
>> CPU: 0 PID: 147 Comm: kworker/u4:3 Not tainted 4.14.0-rc7+ #156
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Workqueue: netns cleanup_net
>> Call Trace:
>>   __dump_stack lib/dump_stack.c:16 [inline]
>>   dump_stack+0x194/0x257 lib/dump_stack.c:52
>>   print_address_description+0x73/0x250 mm/kasan/report.c:252
>>   kasan_report_error mm/kasan/report.c:351 [inline]
>>   kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>   __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>   rds_tcp_kill_sock net/rds/tcp.c:530 [inline]
>>   rds_tcp_dev_event+0xc01/0xc90 net/rds/tcp.c:568
>
>
> The issue here is that we are trying to reference a network namespace
> (struct net *) that is long gone (i.e., L532 below -- c_net is the culprit).
>
>     528         spin_lock_irq(&rds_tcp_conn_lock);
>     529         list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list,
>                      t_tcp_node) {
>     530                 struct net *c_net = tc->t_cpath->cp_conn->c_net;
>     531
>     532                 if (net != c_net || !tc->t_sock)
>     533                         continue;
>     534                 if (!list_has_conn(&tmp_list, tc->t_cpath->cp_conn))
>     535                         list_move_tail(&tc->t_tcp_node, &tmp_list);
>     536         }
>     537         spin_unlock_irq(&rds_tcp_conn_lock);
>     538         list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node) {
>     539                 rds_tcp_conn_paths_destroy(tc->t_cpath->cp_conn);
>     540                 rds_conn_destroy(tc->t_cpath->cp_conn);
>     541         }
>
> When a network namespace is deleted, devices within that namespace are
> unregistered and removed one by one. RDS is notified about this event
> through rds_tcp_dev_event() callback. When the loopback device is removed
> from the namespace, the above RDS callback function destroys all the RDS
> connections in that namespace.
>
> The loop@...9 above walks through each of the rds_tcp connection in the
> global list (rds_tcp_conn_list) to see if that connection belongs to the
> namespace in question. It collects all such connections and destroys them
> (L538-540). However, it leaves behind some of the rds_tcp connections that
> shared the same underlying RDS connection (L534 and 535). These connections
> with pointer to stale network namespace are left behind in the global list.
> When the 2nd network namespace is deleted, we will hit the above stale
> pointer and hit UAF panic.
>
> I think we should move away from global list to a per-namespace list. The
> global list are used only in two places (both of which are per-namespace
> operations):
>
>  - to destroy all the RDS connections belonging to a namespace when the
>    network namespace is being deleted.
>  - to reset all the RDS connections  when socket parameters for a namespace
> are
>    modified using sysctl
>
> Thanks,
> ~Girish


This seems to be fixed with:

#syz fix: rds: tcp: correctly sequence cleanup on netns deletion.

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