[syzbot] WARNING: suspicious RCU usage in __dev_queue_xmit

[syzbot] WARNING: suspicious RCU usage in __dev_queue_xmit

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    4c375272fb0b Merge branch 'net-add-preliminary-netdev-refc..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=164749a9b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2b8e24e3a80e3875
dashboard link: https://syzkaller.appspot.com/bug?extid=e163f2ff7c3f7efd8203
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11493641b00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11ac6aceb00000

The issue was bisected to:

commit 42df6e1d221dddc0f2acf2be37e68d553ad65f96
Author: Lukas Wunner <lukas@wunner.de>
Date:   Fri Oct 8 20:06:03 2021 +0000

    netfilter: Introduce egress hook

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1236329db00000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1136329db00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1636329db00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e163f2ff7c3f7efd8203@syzkaller.appspotmail.com
Fixes: 42df6e1d221d ("netfilter: Introduce egress hook")

=============================
WARNING: suspicious RCU usage
5.16.0-rc3-syzkaller #0 Not tainted
-----------------------------
include/linux/netfilter_netdev.h:97 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by kworker/u4:2/49:
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:635 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:662 [inline]
 #0: ffff88814b0fe938 ((wq_completion)bat_events){+.+.}-{0:0}, at: process_one_work+0x896/0x1690 kernel/workqueue.c:2269
 #1: ffffc9000119fdb0 ((work_completion)(&(&forw_packet_aggr->delayed_work)->work)){+.+.}-{0:0}, at: process_one_work+0x8ca/0x1690 kernel/workqueue.c:2273
 #2: ffffffff8bb83b00 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x1e3/0x3640 net/core/dev.c:4036

stack backtrace:
CPU: 1 PID: 49 Comm: kworker/u4:2 Not tainted 5.16.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 nf_hook_egress include/linux/netfilter_netdev.h:97 [inline]
 __dev_queue_xmit+0x2eac/0x3640 net/core/dev.c:4053
 batadv_send_skb_packet+0x4a9/0x5f0 net/batman-adv/send.c:108
 batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:393 [inline]
 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:421 [inline]
 batadv_iv_send_outstanding_bat_ogm_packet+0x6d7/0x8e0 net/batman-adv/bat_iv_ogm.c:1701
 process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
 kthread+0x405/0x4f0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>


---
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Re: [syzbot] WARNING: suspicious RCU usage in __dev_queue_xmit

[Florian Westphal]

syzbot <syzbot+e163f2ff7c3f7efd8203@syzkaller.appspotmail.com> wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4c375272fb0b Merge branch 'net-add-preliminary-netdev-refc..
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=164749a9b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2b8e24e3a80e3875
> dashboard link: https://syzkaller.appspot.com/bug?extid=e163f2ff7c3f7efd8203
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11493641b00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11ac6aceb00000

> include/linux/netfilter_netdev.h:97 suspicious rcu_dereference_check() usage!

#syz fix: netfilter: egress: avoid a lockdep splat