[v6.1] possible deadlock in nr_rt_ioctl

Hello,

syzbot found the following issue on:

HEAD commit: 7dc732d24ff7 Linux 6.1.123
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13b616c4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=da1827eaa51b65c3
dashboard link: https://syzkaller.appspot.com/bug?extid=780f7126e2ff75d378ec
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b77a36eba7b4/disk-7dc732d2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f5334562da28/vmlinux-7dc732d2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f0a16f9a500c/Image-7dc732d2.gz.xz

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

======================================================
WARNING: possible circular locking dependency detected
6.1.123-syzkaller #0 Not tainted
------------------------------------------------------
syz.4.302/5290 is trying to acquire lock:
ffff800018202b18 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff800018202b18 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffff800018202b18 (nr_neigh_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:472 [inline]
ffff800018202b18 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x328/0xd24 net/netrom/nr_route.c:692

but task is already holding lock:
ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1a4/0xd24 net/netrom/nr_route.c:692

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: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_rt_device_down+0x138/0x6f8 net/netrom/nr_route.c:519
nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
__dev_notify_flags+0x2ac/0x534
dev_change_flags+0xc8/0x154 net/core/dev.c:8669
dev_ifsioc+0x174/0xfbc net/core/dev_ioctl.c:327
dev_ioctl+0x4d8/0xd34 net/core/dev_ioctl.c:588
sock_do_ioctl+0x1dc/0x2dc net/socket.c:1218
sock_ioctl+0x4ec/0x858 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+0x58/0x168 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_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_rt_device_down+0xb8/0x6f8 net/netrom/nr_route.c:517
nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
__dev_notify_flags+0x2ac/0x534
dev_change_flags+0xc8/0x154 net/core/dev.c:8669
dev_ifsioc+0x174/0xfbc net/core/dev_ioctl.c:327
dev_ioctl+0x4d8/0xd34 net/core/dev_ioctl.c:588
sock_do_ioctl+0x1dc/0x2dc net/socket.c:1218
sock_ioctl+0x4ec/0x858 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+0x58/0x168 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_neigh_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+0x3338/0x7680 kernel/locking/lockdep.c:5049
lock_acquire+0x26c/0x7cc 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_remove_neigh net/netrom/nr_route.c:307 [inline]
nr_dec_obs net/netrom/nr_route.c:472 [inline]
nr_rt_ioctl+0x328/0xd24 net/netrom/nr_route.c:692
nr_ioctl+0x14c/0x45c net/netrom/af_netrom.c:1254
sock_do_ioctl+0x134/0x2dc net/socket.c:1204
sock_ioctl+0x4ec/0x858 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+0x58/0x168 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_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.4.302/5290:
#0: ffff800018202b78 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
#0: ffff800018202b78 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:457 [inline]
#0: ffff800018202b78 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x104/0xd24 net/netrom/nr_route.c:692
#1: ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
#1: ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
#1: ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
#1: ffff0000d2cad470 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1a4/0xd24 net/netrom/nr_route.c:692

stack backtrace:
CPU: 0 PID: 5290 Comm: syz.4.302 Not tainted 6.1.123-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call trace:
dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2048
check_noncircular+0x2cc/0x378 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+0x3338/0x7680 kernel/locking/lockdep.c:5049
lock_acquire+0x26c/0x7cc 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_remove_neigh net/netrom/nr_route.c:307 [inline]
nr_dec_obs net/netrom/nr_route.c:472 [inline]
nr_rt_ioctl+0x328/0xd24 net/netrom/nr_route.c:692
nr_ioctl+0x14c/0x45c net/netrom/af_netrom.c:1254
sock_do_ioctl+0x134/0x2dc net/socket.c:1204
sock_ioctl+0x4ec/0x858 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+0x58/0x168 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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Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.