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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