[syzbot] [x25?] possible deadlock in lapbeth_device_event

[syzbot] [x25?] possible deadlock in lapbeth_device_event

[syzbot]

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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Re: [syzbot] [x25?] possible deadlock in lapbeth_device_event

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    1a9239bb4253 Merge tag 'net-next-6.15' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15503804580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=95c3bbe7ce8436a7
dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=139a6bb0580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16974a4c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-1a9239bb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bd56e2f824c3/vmlinux-1a9239bb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/19172b7f9497/bzImage-1a9239bb.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-syzkaller-05877-g1a9239bb4253 #0 Not tainted
--------------------------------------------
dhcpcd/5649 is trying to acquire lock:
ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460

but task is already holding lock:
ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 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/5649:
 #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
 #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x26d/0x1f50 net/ipv4/devinet.c:1121
 #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
 #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
 #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 net/core/dev_api.c:67

stack backtrace:
CPU: 1 UID: 0 PID: 5649 Comm: dhcpcd Not tainted 6.14.0-syzkaller-05877-g1a9239bb4253 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3042
 check_deadlock kernel/locking/lockdep.c:3094 [inline]
 validate_chain kernel/locking/lockdep.c:3896 [inline]
 __lock_acquire+0xff7/0x1ba0 kernel/locking/lockdep.c:5235
 lock_acquire kernel/locking/lockdep.c:5866 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
 __mutex_lock_common kernel/locking/mutex.c:587 [inline]
 __mutex_lock+0x19a/0xb00 kernel/locking/mutex.c:732
 netdev_lock include/linux/netdevice.h:2751 [inline]
 netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
 lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
 lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
 notifier_call_chain+0xb9/0x410 kernel/notifier.c:85
 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2180
 call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
 call_netdevice_notifiers net/core/dev.c:2232 [inline]
 __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9409
 netif_change_flags+0x108/0x160 net/core/dev.c:9438
 dev_change_flags+0xba/0x250 net/core/dev_api.c:68
 devinet_ioctl+0x11d5/0x1f50 net/ipv4/devinet.c:1200
 inet_ioctl+0x3a7/0x3f0 net/ipv4/af_inet.c:1001
 sock_do_ioctl+0x115/0x280 net/socket.c:1190
 sock_ioctl+0x227/0x6b0 net/socket.c:1311
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl fs/ioctl.c:892 [inline]
 __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7effd384cd49
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:00007ffedd440088 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007effd377e6c0 RCX: 00007effd384cd49
RDX: 00007ffedd450278 RSI: 0000000000008914 RDI: 000000000000001a
RBP: 00007ffedd460438 R08: 00007ffedd450238 R09: 00007ffedd4501e8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffedd450278 R14: 0000000000000028 R15: 0000000000008914
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [x25?] possible deadlock in lapbeth_device_event

[Stanislav Fomichev]

On 03/27, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    1a9239bb4253 Merge tag 'net-next-6.15' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15503804580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=95c3bbe7ce8436a7
> dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=139a6bb0580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16974a4c580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-1a9239bb.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/bd56e2f824c3/vmlinux-1a9239bb.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/19172b7f9497/bzImage-1a9239bb.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-syzkaller-05877-g1a9239bb4253 #0 Not tainted
> --------------------------------------------
> dhcpcd/5649 is trying to acquire lock:
> ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
> ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
> ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
> 
> but task is already holding lock:
> ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
> ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 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/5649:
>  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
>  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x26d/0x1f50 net/ipv4/devinet.c:1121
>  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
>  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
>  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
>  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 net/core/dev_api.c:67
> 
> stack backtrace:
> CPU: 1 UID: 0 PID: 5649 Comm: dhcpcd Not tainted 6.14.0-syzkaller-05877-g1a9239bb4253 #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
>  print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3042
>  check_deadlock kernel/locking/lockdep.c:3094 [inline]
>  validate_chain kernel/locking/lockdep.c:3896 [inline]
>  __lock_acquire+0xff7/0x1ba0 kernel/locking/lockdep.c:5235
>  lock_acquire kernel/locking/lockdep.c:5866 [inline]
>  lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
>  __mutex_lock_common kernel/locking/mutex.c:587 [inline]
>  __mutex_lock+0x19a/0xb00 kernel/locking/mutex.c:732
>  netdev_lock include/linux/netdevice.h:2751 [inline]
>  netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
>  lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
>  lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
>  notifier_call_chain+0xb9/0x410 kernel/notifier.c:85
>  call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2180
>  call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
>  call_netdevice_notifiers net/core/dev.c:2232 [inline]
>  __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9409
>  netif_change_flags+0x108/0x160 net/core/dev.c:9438
>  dev_change_flags+0xba/0x250 net/core/dev_api.c:68
>  devinet_ioctl+0x11d5/0x1f50 net/ipv4/devinet.c:1200
>  inet_ioctl+0x3a7/0x3f0 net/ipv4/af_inet.c:1001
>  sock_do_ioctl+0x115/0x280 net/socket.c:1190
>  sock_ioctl+0x227/0x6b0 net/socket.c:1311
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:906 [inline]
>  __se_sys_ioctl fs/ioctl.c:892 [inline]
>  __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7effd384cd49
> 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:00007ffedd440088 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007effd377e6c0 RCX: 00007effd384cd49
> RDX: 00007ffedd450278 RSI: 0000000000008914 RDI: 000000000000001a
> RBP: 00007ffedd460438 R08: 00007ffedd450238 R09: 00007ffedd4501e8
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffedd450278 R14: 0000000000000028 R15: 0000000000008914
>  </TASK>
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.

#syz test

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 56326f38fe8a..a022e930bd8e 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -39,6 +39,7 @@
 #include <linux/lapb.h>
 #include <linux/init.h>
 
+#include <net/netdev_lock.h>
 #include <net/x25device.h>
 
 static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
@@ -372,6 +373,7 @@ static void lapbeth_setup(struct net_device *dev)
 	dev->hard_header_len = 0;
 	dev->mtu             = 1000;
 	dev->addr_len        = 0;
+	netdev_lockdep_set_classes(netdev);
 }
 
 /*	Setup a new device.

Re: [syzbot] [x25?] possible deadlock in lapbeth_device_event

[Eric Dumazet]

On Thu, Mar 27, 2025 at 3:36 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>
> On 03/27, syzbot wrote:
> > syzbot has found a reproducer for the following issue on:
> >
> > HEAD commit:    1a9239bb4253 Merge tag 'net-next-6.15' of git://git.kernel..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15503804580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=95c3bbe7ce8436a7
> > dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
> > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=139a6bb0580000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16974a4c580000
> >
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-1a9239bb.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/bd56e2f824c3/vmlinux-1a9239bb.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/19172b7f9497/bzImage-1a9239bb.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-syzkaller-05877-g1a9239bb4253 #0 Not tainted
> > --------------------------------------------
> > dhcpcd/5649 is trying to acquire lock:
> > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
> > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
> > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
> >
> > but task is already holding lock:
> > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
> > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 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/5649:
> >  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
> >  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x26d/0x1f50 net/ipv4/devinet.c:1121
> >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
> >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 net/core/dev_api.c:67
> >
> > stack backtrace:
> > CPU: 1 UID: 0 PID: 5649 Comm: dhcpcd Not tainted 6.14.0-syzkaller-05877-g1a9239bb4253 #0 PREEMPT(full)
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:94 [inline]
> >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> >  print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3042
> >  check_deadlock kernel/locking/lockdep.c:3094 [inline]
> >  validate_chain kernel/locking/lockdep.c:3896 [inline]
> >  __lock_acquire+0xff7/0x1ba0 kernel/locking/lockdep.c:5235
> >  lock_acquire kernel/locking/lockdep.c:5866 [inline]
> >  lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
> >  __mutex_lock_common kernel/locking/mutex.c:587 [inline]
> >  __mutex_lock+0x19a/0xb00 kernel/locking/mutex.c:732
> >  netdev_lock include/linux/netdevice.h:2751 [inline]
> >  netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
> >  lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
> >  lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
> >  notifier_call_chain+0xb9/0x410 kernel/notifier.c:85
> >  call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2180
> >  call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
> >  call_netdevice_notifiers net/core/dev.c:2232 [inline]
> >  __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9409
> >  netif_change_flags+0x108/0x160 net/core/dev.c:9438
> >  dev_change_flags+0xba/0x250 net/core/dev_api.c:68
> >  devinet_ioctl+0x11d5/0x1f50 net/ipv4/devinet.c:1200
> >  inet_ioctl+0x3a7/0x3f0 net/ipv4/af_inet.c:1001
> >  sock_do_ioctl+0x115/0x280 net/socket.c:1190
> >  sock_ioctl+0x227/0x6b0 net/socket.c:1311
> >  vfs_ioctl fs/ioctl.c:51 [inline]
> >  __do_sys_ioctl fs/ioctl.c:906 [inline]
> >  __se_sys_ioctl fs/ioctl.c:892 [inline]
> >  __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
> >  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> >  do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7effd384cd49
> > 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:00007ffedd440088 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007effd377e6c0 RCX: 00007effd384cd49
> > RDX: 00007ffedd450278 RSI: 0000000000008914 RDI: 000000000000001a
> > RBP: 00007ffedd460438 R08: 00007ffedd450238 R09: 00007ffedd4501e8
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ffedd450278 R14: 0000000000000028 R15: 0000000000008914
> >  </TASK>
> >
> >
> > ---
> > If you want syzbot to run the reproducer, reply with:
> > #syz test: git://repo/address.git branch-or-commit-hash
> > If you attach or paste a git patch, syzbot will apply it before testing.
>
> #syz test
>
> diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
> index 56326f38fe8a..a022e930bd8e 100644
> --- a/drivers/net/wan/lapbether.c
> +++ b/drivers/net/wan/lapbether.c
> @@ -39,6 +39,7 @@
>  #include <linux/lapb.h>
>  #include <linux/init.h>
>
> +#include <net/netdev_lock.h>
>  #include <net/x25device.h>
>
>  static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
> @@ -372,6 +373,7 @@ static void lapbeth_setup(struct net_device *dev)
>         dev->hard_header_len = 0;
>         dev->mtu             = 1000;
>         dev->addr_len        = 0;
> +       netdev_lockdep_set_classes(netdev);
>  }
>
>  /*     Setup a new device.
>

I can resubmit https://lore.kernel.org/netdev/Z84MME6rwU6q9aJa@mini-arch/T/

Re: [syzbot] [x25?] possible deadlock in lapbeth_device_event

[Stanislav Fomichev]

On 03/27, Eric Dumazet wrote:
> On Thu, Mar 27, 2025 at 3:36 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> >
> > On 03/27, syzbot wrote:
> > > syzbot has found a reproducer for the following issue on:
> > >
> > > HEAD commit:    1a9239bb4253 Merge tag 'net-next-6.15' of git://git.kernel..
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15503804580000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=95c3bbe7ce8436a7
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
> > > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=139a6bb0580000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16974a4c580000
> > >
> > > Downloadable assets:
> > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-1a9239bb.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/bd56e2f824c3/vmlinux-1a9239bb.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/19172b7f9497/bzImage-1a9239bb.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-syzkaller-05877-g1a9239bb4253 #0 Not tainted
> > > --------------------------------------------
> > > dhcpcd/5649 is trying to acquire lock:
> > > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
> > > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
> > > ffff888023ad4d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
> > >
> > > but task is already holding lock:
> > > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> > > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
> > > ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 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/5649:
> > >  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
> > >  #0: ffffffff900fb268 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x26d/0x1f50 net/ipv4/devinet.c:1121
> > >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2751 [inline]
> > >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> > >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:39 [inline]
> > >  #1: ffff888029940d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0xa7/0x250 net/core/dev_api.c:67
> > >
> > > stack backtrace:
> > > CPU: 1 UID: 0 PID: 5649 Comm: dhcpcd Not tainted 6.14.0-syzkaller-05877-g1a9239bb4253 #0 PREEMPT(full)
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > > Call Trace:
> > >  <TASK>
> > >  __dump_stack lib/dump_stack.c:94 [inline]
> > >  dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> > >  print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3042
> > >  check_deadlock kernel/locking/lockdep.c:3094 [inline]
> > >  validate_chain kernel/locking/lockdep.c:3896 [inline]
> > >  __lock_acquire+0xff7/0x1ba0 kernel/locking/lockdep.c:5235
> > >  lock_acquire kernel/locking/lockdep.c:5866 [inline]
> > >  lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
> > >  __mutex_lock_common kernel/locking/mutex.c:587 [inline]
> > >  __mutex_lock+0x19a/0xb00 kernel/locking/mutex.c:732
> > >  netdev_lock include/linux/netdevice.h:2751 [inline]
> > >  netif_napi_add_weight include/linux/netdevice.h:2783 [inline]
> > >  lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
> > >  lapbeth_device_event+0x586/0xbe0 drivers/net/wan/lapbether.c:460
> > >  notifier_call_chain+0xb9/0x410 kernel/notifier.c:85
> > >  call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2180
> > >  call_netdevice_notifiers_extack net/core/dev.c:2218 [inline]
> > >  call_netdevice_notifiers net/core/dev.c:2232 [inline]
> > >  __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9409
> > >  netif_change_flags+0x108/0x160 net/core/dev.c:9438
> > >  dev_change_flags+0xba/0x250 net/core/dev_api.c:68
> > >  devinet_ioctl+0x11d5/0x1f50 net/ipv4/devinet.c:1200
> > >  inet_ioctl+0x3a7/0x3f0 net/ipv4/af_inet.c:1001
> > >  sock_do_ioctl+0x115/0x280 net/socket.c:1190
> > >  sock_ioctl+0x227/0x6b0 net/socket.c:1311
> > >  vfs_ioctl fs/ioctl.c:51 [inline]
> > >  __do_sys_ioctl fs/ioctl.c:906 [inline]
> > >  __se_sys_ioctl fs/ioctl.c:892 [inline]
> > >  __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
> > >  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > >  do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
> > >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > > RIP: 0033:0x7effd384cd49
> > > 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:00007ffedd440088 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > > RAX: ffffffffffffffda RBX: 00007effd377e6c0 RCX: 00007effd384cd49
> > > RDX: 00007ffedd450278 RSI: 0000000000008914 RDI: 000000000000001a
> > > RBP: 00007ffedd460438 R08: 00007ffedd450238 R09: 00007ffedd4501e8
> > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > > R13: 00007ffedd450278 R14: 0000000000000028 R15: 0000000000008914
> > >  </TASK>
> > >
> > >
> > > ---
> > > If you want syzbot to run the reproducer, reply with:
> > > #syz test: git://repo/address.git branch-or-commit-hash
> > > If you attach or paste a git patch, syzbot will apply it before testing.
> >
> > #syz test
> >
> > diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
> > index 56326f38fe8a..a022e930bd8e 100644
> > --- a/drivers/net/wan/lapbether.c
> > +++ b/drivers/net/wan/lapbether.c
> > @@ -39,6 +39,7 @@
> >  #include <linux/lapb.h>
> >  #include <linux/init.h>
> >
> > +#include <net/netdev_lock.h>
> >  #include <net/x25device.h>
> >
> >  static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
> > @@ -372,6 +373,7 @@ static void lapbeth_setup(struct net_device *dev)
> >         dev->hard_header_len = 0;
> >         dev->mtu             = 1000;
> >         dev->addr_len        = 0;
> > +       netdev_lockdep_set_classes(netdev);
> >  }
> >
> >  /*     Setup a new device.
> >
> 
> I can resubmit https://lore.kernel.org/netdev/Z84MME6rwU6q9aJa@mini-arch/T/

Ah, this was not pulled because of net vs net-next? Yes, please do!

Re: [syzbot] [x25?] possible deadlock in lapbeth_device_event

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

drivers/net/wan/lapbether.c:376:36: error: 'netdev' undeclared (first use in this function); did you mean 'net_eq'?


Tested on:

commit:         1a9239bb Merge tag 'net-next-6.15' of git://git.kernel..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=95c3bbe7ce8436a7
dashboard link: https://syzkaller.appspot.com/bug?extid=377b71db585c9c705f8e
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15a66bb0580000