[v5.15] possible deadlock in ax25_setsockopt (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc5ec8769306 Linux 5.15.196
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=145e917c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bb6d24ef2164eb
dashboard link: https://syzkaller.appspot.com/bug?extid=7fdffa61d89ddb4e57dc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c71c660545b2/disk-cc5ec876.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f011826cca6/vmlinux-cc5ec876.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8ccd1a2c3f8c/bzImage-cc5ec876.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7fdffa...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.249/5875 is trying to acquire lock:
ffffffff8d238988 (rtnl_mutex){+.+.}-{3:3}, at: ax25_setsockopt+0x830/0xa40 net/ax25/af_ax25.c:676

but task is already holding lock:
ffff88801f40e120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1731 [inline]
ffff88801f40e120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x1d2/0xa40 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+0x44/0x100 net/core/sock.c:3256
lock_sock include/net/sock.h:1731 [inline]
ax25_kill_by_device net/ax25/af_ax25.c:99 [inline]
ax25_device_event+0x217/0x4f0 net/ax25/af_ax25.c:142
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_close_many+0x28d/0x400 net/core/dev.c:1650
dev_close+0x14c/0x200 net/core/dev.c:1672
bpq_device_event+0x2f4/0x9c0 drivers/net/hamradio/bpqether.c:548
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_close_many+0x28d/0x400 net/core/dev.c:1650
dev_close+0x14c/0x200 net/core/dev.c:1672
bond_setup_by_slave+0x61/0x3a0 drivers/net/bonding/bond_main.c:1471
bond_enslave+0x77c/0x3a40 drivers/net/bonding/bond_main.c:1855
bond_do_ioctl+0x2a2/0x8c0 drivers/net/bonding/bond_main.c:4234
bond_siocdevprivate+0x13c/0x320 drivers/net/bonding/bond_main.c:-1
dev_siocdevprivate net/core/dev_ioctl.c:285 [inline]
dev_ifsioc+0xaf5/0xe70 net/core/dev_ioctl.c:403
dev_ioctl+0x5f9/0xe50 net/core/dev_ioctl.c:612
sock_ioctl+0x67b/0x6e0 net/socket.c:1194
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 (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+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
__mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
ax25_setsockopt+0x830/0xa40 net/ax25/af_ax25.c:676
__sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
__do_sys_setsockopt net/socket.c:2224 [inline]
__se_sys_setsockopt net/socket.c:2221 [inline]
__x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
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:

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.6.249/5875:
#0: ffff88801f40e120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1731 [inline]
#0: ffff88801f40e120 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x1d2/0xa40 net/ax25/af_ax25.c:570

stack backtrace:
CPU: 0 PID: 5875 Comm: syz.6.249 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
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
__mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
ax25_setsockopt+0x830/0xa40 net/ax25/af_ax25.c:676
__sys_setsockopt+0x2bf/0x3d0 net/socket.c:2213
__do_sys_setsockopt net/socket.c:2224 [inline]
__se_sys_setsockopt net/socket.c:2221 [inline]
__x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2221
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: 0033:0x7f961c1746c9
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:00007f961a3db038 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007f961c3cafa0 RCX: 00007f961c1746c9
RDX: 0000000000000019 RSI: 0000000000000101 RDI: 0000000000000004
RBP: 00007f961c1f6f91 R08: 0000000000000010 R09: 0000000000000000
R10: 00002000000001c0 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f961c3cb038 R14: 00007f961c3cafa0 R15: 00007ffda9f38b58
</TASK>


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