[v6.1] possible deadlock in nr_rt_device_down

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 563edd786f0a Linux 6.1.122
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=109dd818580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b70d05b26edc7515
dashboard link: https://syzkaller.appspot.com/bug?extid=473934ecefcd67e643fb
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1076fac4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9f111015ce9f/disk-563edd78.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/821c260b7642/vmlinux-563edd78.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9fba8f114c58/bzImage-563edd78.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+473934...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.1.122-syzkaller #0 Tainted: G W
------------------------------------------------------
syz.2.2929/10365 is trying to acquire lock:
ffffffff8e6531d8 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e6531d8 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517

but task is already holding lock:
ffffffff8e653178 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e653178 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x24/0x7b0 net/netrom/nr_route.c:514

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_neigh_list_lock){+...}-{2:2}:
lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]
nr_del_node+0x365/0x6a0 net/netrom/nr_route.c:342
nr_rt_ioctl+0x9f6/0xfb0 net/netrom/nr_route.c:678
sock_do_ioctl+0x152/0x450 net/socket.c:1204
sock_ioctl+0x47f/0x770 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&nr_node->node_lock){+...}-{2:2}:
lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_node_lock include/net/netrom.h:152 [inline]
nr_del_node+0xbc/0x6a0 net/netrom/nr_route.c:335
nr_rt_ioctl+0x9f6/0xfb0 net/netrom/nr_route.c:678
sock_do_ioctl+0x152/0x450 net/socket.c:1204
sock_ioctl+0x47f/0x770 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (nr_node_list_lock){+...}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain+0x1661/0x5950 kernel/locking/lockdep.c:3825
__lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5049
lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517
nr_device_event+0x12b/0x140 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd0/0x170 kernel/notifier.c:455
__dev_notify_flags+0x304/0x610
dev_change_flags+0xe7/0x190 net/core/dev.c:8669
dev_ifsioc+0x177/0x1160 net/core/dev_ioctl.c:327
dev_ioctl+0x508/0xf70 net/core/dev_ioctl.c:588
sock_do_ioctl+0x26b/0x450 net/socket.c:1218
sock_ioctl+0x47f/0x770 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

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

Possible unsafe locking scenario:

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

*** DEADLOCK ***

2 locks held by syz.2.2929/10365:
#0: ffffffff8e50b368 (rtnl_mutex){+.+.}-{3:3}, at: dev_ioctl+0x4f5/0xf70 net/core/dev_ioctl.c:587
#1: ffffffff8e653178 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
#1: ffffffff8e653178 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x24/0x7b0 net/netrom/nr_route.c:514

stack backtrace:
CPU: 0 PID: 10365 Comm: syz.2.2929 Tainted: G W 6.1.122-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
check_noncircular+0x2fa/0x3b0 kernel/locking/lockdep.c:2170
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]
validate_chain+0x1661/0x5950 kernel/locking/lockdep.c:3825
__lock_acquire+0x125b/0x1f80 kernel/locking/lockdep.c:5049
lock_acquire+0x1f8/0x5a0 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_rt_device_down+0xb1/0x7b0 net/netrom/nr_route.c:517
nr_device_event+0x12b/0x140 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd0/0x170 kernel/notifier.c:455
__dev_notify_flags+0x304/0x610
dev_change_flags+0xe7/0x190 net/core/dev.c:8669
dev_ifsioc+0x177/0x1160 net/core/dev_ioctl.c:327
dev_ioctl+0x508/0xf70 net/core/dev_ioctl.c:588
sock_do_ioctl+0x26b/0x450 net/socket.c:1218
sock_ioctl+0x47f/0x770 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f75f7385d29
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:00007f75f8150038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f75f7575fa0 RCX: 00007f75f7385d29
RDX: 0000000020000000 RSI: 0000000000008914 RDI: 0000000000000007
RBP: 00007f75f7401b08 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f75f7575fa0 R15: 00007ffd5b4a5a28
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 325285d9fc86 Linux 6.1.139
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10ec3f68580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6eabc7582f938815
dashboard link: https://syzkaller.appspot.com/bug?extid=473934ecefcd67e643fb
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e29e70580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=164de1f4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f41a9aa4057b/disk-325285d9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/23de5fec8c6f/vmlinux-325285d9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/99bc243c7c24/Image-325285d9.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+473934...@syzkaller.appspotmail.com

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

6.1.139-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor304/4336 is trying to acquire lock:
ffff80001781da18 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff80001781da18 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xb4/0x660 net/netrom/nr_route.c:517

but task is already holding lock:

ffff80001781d9b8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff80001781d9b8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x38/0x660 net/netrom/nr_route.c:514

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_neigh_list_lock){+...}-{2:2}:

__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x54/0x6c kernel/locking/spinlock.c:178

spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_remove_neigh net/netrom/nr_route.c:307 [inline]

nr_del_node+0x35c/0x878 net/netrom/nr_route.c:342
nr_rt_ioctl+0x820/0xb80 net/netrom/nr_route.c:678
nr_ioctl+0x1c4/0x4e4 net/netrom/af_netrom.c:1254
sock_do_ioctl+0xf8/0x240 net/socket.c:1204
sock_ioctl+0x5c4/0x840 net/socket.c:1321

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]

__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (&nr_node->node_lock){+...}-{2:2}:

__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x54/0x6c kernel/locking/spinlock.c:178

spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_node_lock include/net/netrom.h:152 [inline]

nr_del_node+0xbc/0x878 net/netrom/nr_route.c:335
nr_rt_ioctl+0x820/0xb80 net/netrom/nr_route.c:678
nr_ioctl+0x1c4/0x4e4 net/netrom/af_netrom.c:1254
sock_do_ioctl+0xf8/0x240 net/socket.c:1204
sock_ioctl+0x5c4/0x840 net/socket.c:1321

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]

__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #0 (nr_node_list_lock){+...}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]

validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x293c/0x6544 kernel/locking/lockdep.c:5049
lock_acquire+0x20c/0x644 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x54/0x6c kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_rt_device_down+0xb4/0x660 net/netrom/nr_route.c:517
nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
call_netdevice_notifiers_info net/core/dev.c:2001 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
call_netdevice_notifiers net/core/dev.c:2053 [inline]
__dev_notify_flags+0x250/0x46c net/core/dev.c:-1
dev_change_flags+0xc8/0x154 net/core/dev.c:8702
dev_ifsioc+0x524/0xed0 net/core/dev_ioctl.c:327
dev_ioctl+0x4c8/0xc8c net/core/dev_ioctl.c:588
sock_do_ioctl+0x18c/0x240 net/socket.c:1218
sock_ioctl+0x5c4/0x840 net/socket.c:1321

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]

__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

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

Possible unsafe locking scenario:

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

*** DEADLOCK ***

2 locks held by syz-executor304/4336:
#0: ffff8000176d9188 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x20/0x2c net/core/rtnetlink.c:74
#1: ffff80001781d9b8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
#1: ffff80001781d9b8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x38/0x660 net/netrom/nr_route.c:514

stack backtrace:
CPU: 0 PID: 4336 Comm: syz-executor304 Not tainted 6.1.139-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call trace:
dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
__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:2048
check_noncircular+0x240/0x2d4 kernel/locking/lockdep.c:2170

check_prev_add kernel/locking/lockdep.c:3090 [inline]
check_prevs_add kernel/locking/lockdep.c:3209 [inline]

validate_chain kernel/locking/lockdep.c:3825 [inline]
__lock_acquire+0x293c/0x6544 kernel/locking/lockdep.c:5049
lock_acquire+0x20c/0x644 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x54/0x6c kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_rt_device_down+0xb4/0x660 net/netrom/nr_route.c:517
nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
call_netdevice_notifiers_info net/core/dev.c:2001 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
call_netdevice_notifiers net/core/dev.c:2053 [inline]
__dev_notify_flags+0x250/0x46c net/core/dev.c:-1
dev_change_flags+0xc8/0x154 net/core/dev.c:8702
dev_ifsioc+0x524/0xed0 net/core/dev_ioctl.c:327
dev_ioctl+0x4c8/0xc8c net/core/dev_ioctl.c:588
sock_do_ioctl+0x18c/0x240 net/socket.c:1218
sock_ioctl+0x5c4/0x840 net/socket.c:1321

vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]

__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585


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