possible deadlock in cleanup_net

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b36c9697 Add linux-next specific files for 20200828
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15185cc1900000
kernel config: https://syzkaller.appspot.com/x/.config?x=5e3cf99580b5542c
dashboard link: https://syzkaller.appspot.com/bug?extid=d5aa7e0385f6a5d0f4fd
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16e9c761900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1051768e900000

The issue was bisected to:

commit fdeba99b1e58ecd18c2940c453e19e4ef20ff591
Author: Hoang Huu Le <hoang...@dektech.com.au>
Date: Thu Aug 27 02:56:51 2020 +0000

tipc: fix use-after-free in tipc_bcast_get_mode

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=102cd7c5900000
final oops: https://syzkaller.appspot.com/x/report.txt?x=122cd7c5900000
console output: https://syzkaller.appspot.com/x/log.txt?x=142cd7c5900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5aa7e...@syzkaller.appspotmail.com
Fixes: fdeba99b1e58 ("tipc: fix use-after-free in tipc_bcast_get_mode")

======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc2-next-20200828-syzkaller #0 Not tainted
------------------------------------------------------
kworker/u4:6/349 is trying to acquire lock:
ffff8880aa063d38 ((wq_completion)events){+.+.}-{0:0}, at: flush_workqueue+0xe1/0x13e0 kernel/workqueue.c:2777

but task is already holding lock:
ffffffff8a879430 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x9b/0xb10 net/core/net_namespace.c:565

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (pernet_ops_rwsem){++++}-{3:3}:
down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
unregister_netdevice_notifier+0x1e/0x170 net/core/dev.c:1861
bcm_release+0x94/0x750 net/can/bcm.c:1474
__sock_release+0xcd/0x280 net/socket.c:596
sock_close+0x18/0x20 net/socket.c:1277
__fput+0x285/0x920 fs/file_table.c:281
task_work_run+0xdd/0x190 kernel/task_work.c:141
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop kernel/entry/common.c:140 [inline]
exit_to_user_mode_prepare+0x195/0x1c0 kernel/entry/common.c:167
syscall_exit_to_user_mode+0x59/0x2b0 kernel/entry/common.c:242
entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #2 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}:
down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
inode_lock include/linux/fs.h:779 [inline]
__sock_release+0x86/0x280 net/socket.c:595
sock_close+0x18/0x20 net/socket.c:1277
__fput+0x285/0x920 fs/file_table.c:281
delayed_fput+0x56/0x70 fs/file_table.c:309
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #1 ((delayed_fput_work).work){+.+.}-{0:0}:
process_one_work+0x8bb/0x1670 kernel/workqueue.c:2245
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #0 ((wq_completion)events){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a6b/0x5640 kernel/locking/lockdep.c:4426
lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
flush_workqueue+0x110/0x13e0 kernel/workqueue.c:2780
flush_scheduled_work include/linux/workqueue.h:597 [inline]
tipc_exit_net+0x47/0x2a0 net/tipc/core.c:116
ops_exit_list+0xb0/0x160 net/core/net_namespace.c:186
cleanup_net+0x4ea/0xb10 net/core/net_namespace.c:603
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

other info that might help us debug this:

Chain exists of:
(wq_completion)events --> &sb->s_type->i_mutex_key#13 --> pernet_ops_rwsem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(pernet_ops_rwsem);
lock(&sb->s_type->i_mutex_key#13);
lock(pernet_ops_rwsem);
lock((wq_completion)events);

*** DEADLOCK ***

3 locks held by kworker/u4:6/349:
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
#0: ffff8880a97b1138 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x82b/0x1670 kernel/workqueue.c:2240
#1: ffffc900020e7da8 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x85f/0x1670 kernel/workqueue.c:2244
#2: ffffffff8a879430 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x9b/0xb10 net/core/net_namespace.c:565

stack backtrace:
CPU: 1 PID: 349 Comm: kworker/u4:6 Not tainted 5.9.0-rc2-next-20200828-syzkaller #0
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:77 [inline]
dump_stack+0x18f/0x20d lib/dump_stack.c:118
check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a6b/0x5640 kernel/locking/lockdep.c:4426
lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
flush_workqueue+0x110/0x13e0 kernel/workqueue.c:2780
flush_scheduled_work include/linux/workqueue.h:597 [inline]
tipc_exit_net+0x47/0x2a0 net/tipc/core.c:116
ops_exit_list+0xb0/0x160 net/core/net_namespace.c:186
cleanup_net+0x4ea/0xb10 net/core/net_namespace.c:603
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415


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