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

Stanislav Fomichev
2025-03-27T14:44:01Z

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!