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

Stanislav Fomichev
2025-03-27T14:36:24Z

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.