* [syzbot] [kernfs?] possible deadlock in kernfs_iop_permission (2)
@ 2026-07-19 18:17 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-07-19 18:17 UTC (permalink / raw)
To: driver-core, gregkh, linux-kernel, netdev, syzkaller-bugs, tj
Hello,
syzbot found the following issue on:
HEAD commit: 3f1f75536668 net: openvswitch: reject oversized nested act..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=108e8789580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5c4196ba0e33631d
dashboard link: https://syzkaller.appspot.com/bug?extid=90c39e7098489ce1def1
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/38c0534858bd/disk-3f1f7553.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3140a6e2252d/vmlinux-3f1f7553.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f8a7156a6da0/bzImage-3f1f7553.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+90c39e7098489ce1def1@syzkaller.appspotmail.com
netlink: 'syz.3.10493': attribute type 1 has an invalid length.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.10493/14209 is trying to acquire lock:
ffff88801c294210 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_permission+0x7f/0x430 fs/kernfs/inode.c:288
but task is already holding lock:
ffffffff8e9e75f0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2535 [inline]
ffffffff8e9e75f0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_procs_write_start+0x539/0x900 kernel/cgroup/cgroup.c:3100
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #7 (cpu_hotplug_lock){++++}-{0:0}:
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
cpus_read_lock+0x42/0x160 kernel/cpu.c:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
nbd_reconnect_socket drivers/block/nbd.c:1379 [inline]
nbd_genl_reconfigure+0x1301/0x1e80 drivers/block/nbd.c:2468
genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
__sock_sendmsg net/socket.c:790 [inline]
____sys_sendmsg+0x54e/0x850 net/socket.c:2684
___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
__sys_sendmsg net/socket.c:2770 [inline]
__do_sys_sendmsg net/socket.c:2775 [inline]
__se_sys_sendmsg net/socket.c:2773 [inline]
__x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x373/0x1150 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2117
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
__blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #5 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
nbd_queue_rq+0xc1/0x1150 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2117
__blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
__blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #4 (set->srcu){.+.+}-{0:0}:
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xc9/0x2f0 kernel/rcu/srcutree.c:1481
elevator_switch+0x1e8/0x7b0 block/elevator.c:576
elevator_change+0x2fa/0x480 block/elevator.c:681
elevator_set_default+0x375/0x440 block/elevator.c:754
blk_register_queue+0x3f3/0x4e0 block/blk-sysfs.c:992
__add_disk+0x6cb/0xe30 block/genhd.c:528
add_disk_fwnode+0xfb/0x4b0 block/genhd.c:597
add_disk include/linux/blkdev.h:800 [inline]
nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2021
nbd_init+0x15f/0x1e0 drivers/block/nbd.c:2729
do_one_initcall+0x250/0x870 init/main.c:1347
do_initcall_level+0x10a/0x1a0 init/main.c:1409
do_initcalls+0x59/0xa0 init/main.c:1425
kernel_init_freeable+0x29d/0x3e0 init/main.c:1658
kernel_init+0x1d/0x1d0 init/main.c:1548
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #3 (&q->elevator_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
elevator_change+0x1af/0x480 block/elevator.c:679
elevator_set_none+0xb5/0x140 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5101 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5146 [inline]
blk_mq_update_nr_hw_queues+0x5ef/0x19f0 block/blk-mq.c:5211
nbd_start_device+0x189/0xb30 drivers/block/nbd.c:1526
nbd_genl_connect+0x1597/0x1c10 drivers/block/nbd.c:2276
genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
__sock_sendmsg net/socket.c:790 [inline]
____sys_sendmsg+0x54e/0x850 net/socket.c:2684
___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
__sys_sendmsg net/socket.c:2770 [inline]
__do_sys_sendmsg net/socket.c:2775 [inline]
__se_sys_sendmsg net/socket.c:2773 [inline]
__x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&q->q_usage_counter(io)#52){++++}-{0:0}:
blk_alloc_queue+0x544/0x690 block/blk-core.c:504
blk_mq_alloc_queue block/blk-mq.c:4420 [inline]
__blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4467
nbd_dev_add+0x494/0xb60 drivers/block/nbd.c:1991
nbd_init+0x15f/0x1e0 drivers/block/nbd.c:2729
do_one_initcall+0x250/0x870 init/main.c:1347
do_initcall_level+0x10a/0x1a0 init/main.c:1409
do_initcalls+0x59/0xa0 init/main.c:1425
kernel_init_freeable+0x29d/0x3e0 init/main.c:1658
kernel_init+0x1d/0x1d0 init/main.c:1548
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4329 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4343
might_alloc include/linux/sched/mm.h:317 [inline]
slab_pre_alloc_hook mm/slub.c:4565 [inline]
slab_alloc_node mm/slub.c:4925 [inline]
kmem_cache_alloc_noprof+0x64/0x5f0 mm/slub.c:4959
__kernfs_iattrs+0xdd/0x380 fs/kernfs/inode.c:36
kernfs_iattrs fs/kernfs/inode.c:60 [inline]
__kernfs_setattr fs/kernfs/inode.c:73 [inline]
kernfs_iop_setattr+0xe6/0x3f0 fs/kernfs/inode.c:127
notify_change+0xbba/0xea0 fs/attr.c:556
do_truncate+0x1c2/0x250 fs/open.c:68
handle_truncate fs/namei.c:4305 [inline]
do_open fs/namei.c:4704 [inline]
path_openat+0x2fed/0x3830 fs/namei.c:4863
do_file_open+0x23e/0x4a0 fs/namei.c:4892
do_sys_openat2+0x115/0x200 fs/open.c:1368
do_sys_open fs/open.c:1374 [inline]
__do_sys_openat fs/open.c:1390 [inline]
__se_sys_openat fs/open.c:1385 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1385
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
down_read+0x4a/0x330 kernel/locking/rwsem.c:1574
kernfs_iop_permission+0x7f/0x430 fs/kernfs/inode.c:288
do_inode_permission fs/namei.c:583 [inline]
inode_permission+0x3de/0x5f0 fs/namei.c:653
cgroup_may_write kernel/cgroup/cgroup.c:5325 [inline]
cgroup_procs_write_permission kernel/cgroup/cgroup.c:5345 [inline]
cgroup_attach_permissions+0x28e/0x9f0 kernel/cgroup/cgroup.c:5368
__cgroup_procs_write+0x24b/0x320 kernel/cgroup/cgroup.c:5411
cgroup_threads_write+0x24/0x50 kernel/cgroup/cgroup.c:5441
cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4316
kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x612/0xba0 fs/read_write.c:687
ksys_write+0x150/0x270 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&root->kernfs_iattr_rwsem --> &nsock->tx_lock --> cpu_hotplug_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(cpu_hotplug_lock);
lock(&nsock->tx_lock);
lock(cpu_hotplug_lock);
rlock(&root->kernfs_iattr_rwsem);
*** DEADLOCK ***
4 locks held by syz.3.10493/14209:
#0: ffff8880355be450 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2733 [inline]
#0: ffff8880355be450 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
#1: ffff888029df8c80 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540 fs/kernfs/file.c:336
#2: ffffffff8eb99560 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_lock include/linux/cgroup.h:456 [inline]
#2: ffffffff8eb99560 (cgroup_mutex){+.+.}-{4:4}, at: cgroup_kn_lock_live+0x13c/0x230 kernel/cgroup/cgroup.c:1717
#3: ffffffff8e9e75f0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock kernel/cgroup/cgroup.c:2535 [inline]
#3: ffffffff8e9e75f0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_procs_write_start+0x539/0x900 kernel/cgroup/cgroup.c:3100
stack backtrace:
CPU: 0 UID: 0 PID: 14209 Comm: syz.3.10493 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
down_read+0x4a/0x330 kernel/locking/rwsem.c:1574
kernfs_iop_permission+0x7f/0x430 fs/kernfs/inode.c:288
do_inode_permission fs/namei.c:583 [inline]
inode_permission+0x3de/0x5f0 fs/namei.c:653
cgroup_may_write kernel/cgroup/cgroup.c:5325 [inline]
cgroup_procs_write_permission kernel/cgroup/cgroup.c:5345 [inline]
cgroup_attach_permissions+0x28e/0x9f0 kernel/cgroup/cgroup.c:5368
__cgroup_procs_write+0x24b/0x320 kernel/cgroup/cgroup.c:5411
cgroup_threads_write+0x24/0x50 kernel/cgroup/cgroup.c:5441
cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4316
kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x612/0xba0 fs/read_write.c:687
ksys_write+0x150/0x270 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3c8819de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3c890ee028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f3c88425fa0 RCX: 00007f3c8819de59
RDX: 0000000000000012 RSI: 0000200000000c40 RDI: 000000000000000b
RBP: 00007f3c88233e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3c88426038 R14: 00007f3c88425fa0 R15: 00007fffbdb3ac08
</TASK>
---
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2026-07-19 18:17 [syzbot] [kernfs?] possible deadlock in kernfs_iop_permission (2) syzbot
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