[v5.15] possible deadlock in nr_del_node

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 16fdf2c7111b Linux 5.15.181
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=114f7774580000
kernel config: https://syzkaller.appspot.com/x/.config?x=78ce1ad3d91bc375
dashboard link: https://syzkaller.appspot.com/bug?extid=66b03f76f8433672c99b
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cbc22554cbd8/disk-16fdf2c7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d03dacaa22f5/vmlinux-16fdf2c7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b3dc7f1264c1/Image-16fdf2c7.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+66b03f...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): bpq0: link becomes ready
======================================================
WARNING: possible circular locking dependency detected
5.15.181-syzkaller #0 Not tainted
------------------------------------------------------
syz.1.31/4297 is trying to acquire lock:
ffff8000163aa5f8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff8000163aa5f8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffff8000163aa5f8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_del_node+0x368/0x8ec net/netrom/nr_route.c:342

but task is already holding lock:
ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: nr_del_node+0xc0/0x8ec net/netrom/nr_route.c:335

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{2:2}:
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x114/0x1b4 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_node_lock include/net/netrom.h:151 [inline]
nr_del_node+0xc0/0x8ec net/netrom/nr_route.c:335
nr_rt_ioctl+0x92c/0xe2c net/netrom/nr_route.c:678
nr_ioctl+0x1c4/0x51c net/netrom/af_netrom.c:1253
sock_do_ioctl+0xf8/0x240 net/socket.c:1140
sock_ioctl+0x5c8/0x87c net/socket.c:1257
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #1 (nr_node_list_lock){+...}-{2:2}:
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x114/0x1b4 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_rt_device_down+0xb4/0x690 net/netrom/nr_route.c:517
nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
call_netdevice_notifiers_info net/core/dev.c:2049 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
call_netdevice_notifiers net/core/dev.c:2075 [inline]
__dev_notify_flags+0x250/0x46c net/core/dev.c:-1
dev_change_flags+0xc8/0x154 net/core/dev.c:8929
dev_ifsioc+0x504/0xef4 net/core/dev_ioctl.c:324
dev_ioctl+0x4d0/0xc94 net/core/dev_ioctl.c:587
sock_do_ioctl+0x18c/0x240 net/socket.c:1154
sock_ioctl+0x5c8/0x87c net/socket.c:1257
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (nr_neigh_list_lock){+...}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2928/0x651c kernel/locking/lockdep.c:5012
lock_acquire+0x1f4/0x620 kernel/locking/lockdep.c:5623
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x114/0x1b4 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]
nr_del_node+0x368/0x8ec net/netrom/nr_route.c:342
nr_rt_ioctl+0x92c/0xe2c net/netrom/nr_route.c:678
nr_ioctl+0x1c4/0x51c net/netrom/af_netrom.c:1253
sock_do_ioctl+0xf8/0x240 net/socket.c:1140
sock_ioctl+0x5c8/0x87c net/socket.c:1257
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:
nr_neigh_list_lock --> nr_node_list_lock --> &nr_node->node_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&nr_node->node_lock);
lock(nr_node_list_lock);
lock(&nr_node->node_lock);
lock(nr_neigh_list_lock);

*** DEADLOCK ***

2 locks held by syz.1.31/4297:
#0: ffff8000163aa658 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
#0: ffff8000163aa658 (nr_node_list_lock){+...}-{2:2}, at: nr_del_node+0x60/0x8ec net/netrom/nr_route.c:334
#1: ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
#1: ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
#1: ffff0000c89d4270 (&nr_node->node_lock){+...}-{2:2}, at: nr_del_node+0xc0/0x8ec net/netrom/nr_route.c:335

stack backtrace:
CPU: 0 PID: 4297 Comm: syz.1.31 Not tainted 5.15.181-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
Call trace:
dump_backtrace+0x0/0x43c arch/arm64/kernel/stacktrace.c:152
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
__dump_stack+0x30/0x40 lib/dump_stack.c:88
dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106
dump_stack+0x1c/0x5c lib/dump_stack.c:113
print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2011
check_noncircular+0x240/0x2d4 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2928/0x651c kernel/locking/lockdep.c:5012
lock_acquire+0x1f4/0x620 kernel/locking/lockdep.c:5623
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x114/0x1b4 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]
nr_del_node+0x368/0x8ec net/netrom/nr_route.c:342
nr_rt_ioctl+0x92c/0xe2c net/netrom/nr_route.c:678
nr_ioctl+0x1c4/0x51c net/netrom/af_netrom.c:1253
sock_do_ioctl+0xf8/0x240 net/socket.c:1140
sock_ioctl+0x5c8/0x87c net/socket.c:1257
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: c79648372d02 Linux 5.15.189
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16398034580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f3b1215b3cf4119f
dashboard link: https://syzkaller.appspot.com/bug?extid=66b03f76f8433672c99b
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=131da8a2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=161e48a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/fa511d2a8893/disk-c7964837.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f14b6c77bbb9/vmlinux-c7964837.xz
kernel image: https://storage.googleapis.com/syzbot-assets/388987ba15c6/bzImage-c7964837.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+66b03f...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected

5.15.189-syzkaller #0 Not tainted
------------------------------------------------------
syz.1.759/5160 is trying to acquire lock:
ffffffff8d36d418 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffffffff8d36d418 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffffffff8d36d418 (nr_neigh_list_lock){+...}-{2:2}, at: nr_del_node+0x512/0x8d0 net/netrom/nr_route.c:342

but task is already holding lock:

ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: nr_del_node+0x152/0x8d0 net/netrom/nr_route.c:335

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{2:2}:
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]

_raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178

spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_node_lock include/net/netrom.h:151 [inline]

nr_rt_device_down+0x126/0x710 net/netrom/nr_route.c:519
nr_device_event+0x133/0x140 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391

call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
call_netdevice_notifiers net/core/dev.c:2075 [inline]

__dev_notify_flags+0x178/0x2d0 net/core/dev.c:-1
dev_change_flags+0xe3/0x1a0 net/core/dev.c:8929
dev_ifsioc+0x147/0xe70 net/core/dev_ioctl.c:324
dev_ioctl+0x55f/0xe50 net/core/dev_ioctl.c:587
sock_do_ioctl+0x222/0x2f0 net/socket.c:1154
sock_ioctl+0x4ed/0x6e0 net/socket.c:1257

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]

__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (nr_node_list_lock){+...}-{2:2}:
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]

_raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_rt_device_down+0xa5/0x710 net/netrom/nr_route.c:517
nr_device_event+0x133/0x140 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391

call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
call_netdevice_notifiers net/core/dev.c:2075 [inline]

__dev_notify_flags+0x178/0x2d0 net/core/dev.c:-1
dev_change_flags+0xe3/0x1a0 net/core/dev.c:8929
dev_ifsioc+0x147/0xe70 net/core/dev_ioctl.c:324
dev_ioctl+0x55f/0xe50 net/core/dev_ioctl.c:587
sock_do_ioctl+0x222/0x2f0 net/socket.c:1154
sock_ioctl+0x4ed/0x6e0 net/socket.c:1257

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]

__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (nr_neigh_list_lock){+...}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]

__lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178

spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]

nr_del_node+0x512/0x8d0 net/netrom/nr_route.c:342
nr_rt_ioctl+0x982/0xce0 net/netrom/nr_route.c:678
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1140
sock_ioctl+0x4ed/0x6e0 net/socket.c:1257

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]

__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
nr_neigh_list_lock --> nr_node_list_lock --> &nr_node->node_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&nr_node->node_lock);
lock(nr_node_list_lock);
lock(&nr_node->node_lock);
lock(nr_neigh_list_lock);

*** DEADLOCK ***

2 locks held by syz.1.759/5160:
#0: ffffffff8d36d478 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
#0: ffffffff8d36d478 (nr_node_list_lock){+...}-{2:2}, at: nr_del_node+0xfc/0x8d0 net/netrom/nr_route.c:334
#1: ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
#1: ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
#1: ffff888024445870 (&nr_node->node_lock){+...}-{2:2}, at: nr_del_node+0x152/0x8d0 net/netrom/nr_route.c:335

stack backtrace:
CPU: 1 PID: 5160 Comm: syz.1.759 Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2133

check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]

__lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178

spin_lock_bh include/linux/spinlock.h:368 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]

nr_del_node+0x512/0x8d0 net/netrom/nr_route.c:342
nr_rt_ioctl+0x982/0xce0 net/netrom/nr_route.c:678
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1140
sock_ioctl+0x4ed/0x6e0 net/socket.c:1257

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]

__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f055ec269a9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda3395a58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f055ee4dfa0 RCX: 00007f055ec269a9
RDX: 0000200000000680 RSI: 000000000000890c RDI: 0000000000000005
RBP: 00007f055eca8d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f055ee4dfa0 R14: 00007f055ee4dfa0 R15: 0000000000000003
</TASK>


---
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