Subject: Re: WARNING: suspicious RCU usage in tipc_l2_send_msg

From: syzbot <[email-masked]>
Date: Mon, 13 Jul 2020 01:05:18 -0700

syzbot has found a reproducer for the following crash on:

HEAD commit:    4437dd6e Merge tag 'io_uring-5.8-2020-07-12' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17b7869f100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=66ad203c2bb6d8b
dashboard link: https://syzkaller.appspot.com/bug?extid=47bbc6b678d317cccbe0
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10c005af100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

=============================
WARNING: suspicious RCU usage
5.8.0-rc4-syzkaller #0 Not tainted
-----------------------------
net/tipc/bearer.c:466 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
2 locks held by kworker/0:1/12:
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff88821adc9538 ((wq_completion)cryptd){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
 #1: ffffc90000d2fda8 ((work_completion)(&cpu_queue->work)){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244

stack backtrace:
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.8.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: cryptd cryptd_queue_worker
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 tipc_l2_send_msg+0x354/0x420 net/tipc/bearer.c:466
 tipc_aead_encrypt_done+0x204/0x3a0 net/tipc/crypto.c:761
 cryptd_aead_crypt+0xe8/0x1d0 crypto/cryptd.c:739
 cryptd_queue_worker+0x118/0x1b0 crypto/cryptd.c:181
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293