[syzbot] [x25?] possible deadlock in lapbeth_device_event

syzbot
2025-03-09T09:36:29Z

Hello,

syzbot found the following issue on:

HEAD commit: 8ef890df4031 net: move misc netdev_lock flavors to a separ..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=149cd878580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ca99d9d1f4a8ecfa
dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
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=1054d4b7980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ed25b0258c8e/disk-8ef890df.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2989aa28823e/vmlinux-8ef890df.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0e040be79a3d/bzImage-8ef890df.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+377b71db585c9c705f8e@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.14.0-rc5-syzkaller-01147-g8ef890df4031 #0 Not tainted
--------------------------------------------
dhcpcd/5500 is trying to acquire lock:
ffff888031330d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
ffff888031330d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2763 [inline]
ffff888031330d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
ffff888031330d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x766/0xa20 drivers/net/wan/lapbether.c:460

but task is already holding lock:
ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:40 [inline]
ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0x120/0x270 net/core/dev_api.c:67

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&dev->lock);
lock(&dev->lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by dhcpcd/5500:
#0: ffffffff8fed6908 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
#0: ffffffff8fed6908 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x34c/0x1d80 net/ipv4/devinet.c:1121
#1: ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
#1: ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:40 [inline]
#1: ffff88806408cd28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0x120/0x270 net/core/dev_api.c:67

stack backtrace:
CPU: 0 UID: 0 PID: 5500 Comm: dhcpcd Not tainted 6.14.0-rc5-syzkaller-01147-g8ef890df4031 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
check_deadlock kernel/locking/lockdep.c:3091 [inline]
validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
__lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
netdev_lock include/linux/netdevice.h:2731 [inline]
netif_napi_add_weight include/linux/netdevice.h:2763 [inline]
lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
lapbeth_device_event+0x766/0xa20 drivers/net/wan/lapbether.c:460
notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85
__dev_notify_flags+0x207/0x400
netif_change_flags+0xf0/0x1a0 net/core/dev.c:9443
dev_change_flags+0x146/0x270 net/core/dev_api.c:68
devinet_ioctl+0xea2/0x1d80 net/ipv4/devinet.c:1200
inet_ioctl+0x3d7/0x4f0 net/ipv4/af_inet.c:1001
sock_do_ioctl+0x158/0x460 net/socket.c:1190
sock_ioctl+0x626/0x8e0 net/socket.c:1309
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcdbbcb2d49
Code: 5c c3 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 10 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 76 10 48 8b 15 ae 60 0d 00 f7 d8 41 83 c8
RSP: 002b:00007ffecf47b768 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fcdbbbe46c0 RCX: 00007fcdbbcb2d49
RDX: 00007ffecf48b958 RSI: 0000000000008914 RDI: 000000000000000c
RBP: 00007ffecf49bb18 R08: 00007ffecf48b918 R09: 00007ffecf48b8c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffecf48b958 R14: 0000000000000028 R15: 0000000000008914
</TASK>

---
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