[v5.15] possible deadlock in rtnl_lock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c16c81c81336 Linux 5.15.178
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=111b2a64580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3ca28fba9b2e5c5
dashboard link: https://syzkaller.appspot.com/bug?extid=8d3fcc0190951c1256dd
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/3f2947e5e4dc/disk-c16c81c8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7034800fdaa8/vmlinux-c16c81c8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/42337be7c213/Image-c16c81c8.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8d3fcc...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.15.178-syzkaller #0 Not tainted
------------------------------------------------------
syz.9.971/9810 is trying to acquire lock:
ffff800016cb4be8 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x20/0x2c net/core/rtnetlink.c:72

but task is already holding lock:
ffff0000d686a120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1684 [inline]
ffff0000d686a120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x2b0/0xcdc net/ax25/af_ax25.c:570

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_AX25){+.+.}-{0:0}:
lock_sock_nested+0xec/0x1ec net/core/sock.c:3253
lock_sock include/net/sock.h:1684 [inline]
ax25_kill_by_device net/ax25/af_ax25.c:99 [inline]
ax25_device_event+0x208/0x58c net/ax25/af_ax25.c:142
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
__dev_notify_flags+0x2ac/0x534
dev_change_flags+0xc8/0x154 net/core/dev.c:8897
dev_ifsioc+0x140/0xfe4 net/core/dev_ioctl.c:324
dev_ioctl+0x4e0/0xd3c net/core/dev_ioctl.c:587
sock_do_ioctl+0x1dc/0x2dc net/socket.c:1154
sock_ioctl+0x4f0/0x8ac 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+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (rtnl_mutex){+.+.}-{3:3}:
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+0x32d4/0x7638 kernel/locking/lockdep.c:5012
lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
__mutex_lock_common+0x194/0x2154 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0xa4/0xf8 kernel/locking/mutex.c:743
rtnl_lock+0x20/0x2c net/core/rtnetlink.c:72
ax25_setsockopt+0x91c/0xcdc net/ax25/af_ax25.c:676
__sys_setsockopt+0x3a8/0x6b4 net/socket.c:2203
__do_sys_setsockopt net/socket.c:2214 [inline]
__se_sys_setsockopt net/socket.c:2211 [inline]
__arm64_sys_setsockopt+0xb8/0xd4 net/socket.c:2211
__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+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 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:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sk_lock-AF_AX25);
lock(rtnl_mutex);
lock(sk_lock-AF_AX25);
lock(rtnl_mutex);

*** DEADLOCK ***

1 lock held by syz.9.971/9810:
#0: ffff0000d686a120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1684 [inline]
#0: ffff0000d686a120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x2b0/0xcdc net/ax25/af_ax25.c:570

stack backtrace:
CPU: 1 PID: 9810 Comm: syz.9.971 Not tainted 5.15.178-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call trace:
dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
__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:2011
check_noncircular+0x2cc/0x378 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+0x32d4/0x7638 kernel/locking/lockdep.c:5012
lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
__mutex_lock_common+0x194/0x2154 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0xa4/0xf8 kernel/locking/mutex.c:743
rtnl_lock+0x20/0x2c net/core/rtnetlink.c:72
ax25_setsockopt+0x91c/0xcdc net/ax25/af_ax25.c:676
__sys_setsockopt+0x3a8/0x6b4 net/socket.c:2203
__do_sys_setsockopt net/socket.c:2214 [inline]
__se_sys_setsockopt net/socket.c:2211 [inline]
__arm64_sys_setsockopt+0xb8/0xd4 net/socket.c:2211
__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+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.