Message-ID: <685af3b1.a00a0220.2e5631.0091.GAE@google.com>
Date: Tue, 24 Jun 2025 11:51:29 -0700
From: syzbot <syzbot+e67ea9c235b13b4f0020@...kaller.appspotmail.com>
To: andrii@...nel.org, ast@...nel.org, bjorn@...nel.org, bpf@...r.kernel.org, 
	daniel@...earbox.net, davem@...emloft.net, edumazet@...gle.com, 
	horms@...nel.org, jonathan.lemon@...il.com, kuba@...nel.org, 
	linux-kernel@...r.kernel.org, maciej.fijalkowski@...el.com, 
	magnus.karlsson@...el.com, netdev@...r.kernel.org, pabeni@...hat.com, 
	sdf@...ichev.me, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [bpf?] [net?] possible deadlock in xsk_notifier (3)

Hello,

syzbot found the following issue on:

HEAD commit:    78f4e737a53e Merge tag 'for-6.16/dm-fixes' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b48f0c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=12ec1a20ad573841
dashboard link: https://syzkaller.appspot.com/bug?extid=e67ea9c235b13b4f0020
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3ff97b2d201b/disk-78f4e737.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1968f46c8915/vmlinux-78f4e737.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3455e371b965/bzImage-78f4e737.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e67ea9c235b13b4f0020@...kaller.appspotmail.com

netlink: 4 bytes leftover after parsing attributes in process `syz.1.1331'.
======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc3-syzkaller-00042-g78f4e737a53e #0 Not tainted
------------------------------------------------------
syz.1.1331/11144 is trying to acquire lock:
ffff888054b136b0 (&xs->mutex){+.+.}-{4:4}, at: xsk_notifier+0x101/0x280 net/xdp/xsk.c:1649

but task is already holding lock:
ffff888052f43d58 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_notifier+0xa4/0x280 net/xdp/xsk.c:1645

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&net->xdp.lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       xsk_notifier+0xa4/0x280 net/xdp/xsk.c:1645
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
       call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
       call_netdevice_notifiers net/core/dev.c:2282 [inline]
       unregister_netdevice_many_notify+0xf9d/0x2700 net/core/dev.c:12077
       unregister_netdevice_many net/core/dev.c:12140 [inline]
       unregister_netdevice_queue+0x305/0x3f0 net/core/dev.c:11984
       register_netdevice+0x18f1/0x2270 net/core/dev.c:11149
       lapbeth_new_device drivers/net/wan/lapbether.c:420 [inline]
       lapbeth_device_event+0x5b1/0xbe0 drivers/net/wan/lapbether.c:462
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
       call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
       call_netdevice_notifiers net/core/dev.c:2282 [inline]
       __dev_notify_flags+0x12c/0x2e0 net/core/dev.c:9497
       netif_change_flags+0x108/0x160 net/core/dev.c:9526
       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+0x118/0x280 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:907 [inline]
       __se_sys_ioctl fs/ioctl.c:893 [inline]
       __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&dev_instance_lock_key#20){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       netdev_lock include/linux/netdevice.h:2756 [inline]
       netdev_lock_ops include/net/netdev_lock.h:42 [inline]
       xsk_bind+0x37c/0x1570 net/xdp/xsk.c:1189
       __sys_bind_socket net/socket.c:1810 [inline]
       __sys_bind_socket net/socket.c:1802 [inline]
       __sys_bind+0x1a7/0x260 net/socket.c:1841
       __do_sys_bind net/socket.c:1846 [inline]
       __se_sys_bind net/socket.c:1844 [inline]
       __x64_sys_bind+0x72/0xb0 net/socket.c:1844
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&xs->mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain kernel/locking/lockdep.c:3911 [inline]
       __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
       lock_acquire kernel/locking/lockdep.c:5871 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       xsk_notifier+0x101/0x280 net/xdp/xsk.c:1649
       notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
       call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
       call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
       call_netdevice_notifiers net/core/dev.c:2282 [inline]
       unregister_netdevice_many_notify+0xf9d/0x2700 net/core/dev.c:12077
       rtnl_delete_link net/core/rtnetlink.c:3511 [inline]
       rtnl_dellink+0x3cb/0xa80 net/core/rtnetlink.c:3553
       rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6944
       netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2534
       netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
       netlink_unicast+0x53d/0x7f0 net/netlink/af_netlink.c:1339
       netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883
       sock_sendmsg_nosec net/socket.c:712 [inline]
       __sock_sendmsg net/socket.c:727 [inline]
       ____sys_sendmsg+0xa98/0xc70 net/socket.c:2566
       ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620
       __sys_sendmsg+0x16d/0x220 net/socket.c:2652
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &xs->mutex --> &dev_instance_lock_key#20 --> &net->xdp.lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&net->xdp.lock);
                               lock(&dev_instance_lock_key#20);
                               lock(&net->xdp.lock);
  lock(&xs->mutex);

 *** DEADLOCK ***

2 locks held by syz.1.1331/11144:
 #0: ffffffff9034e4a8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff9034e4a8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
 #0: ffffffff9034e4a8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dellink+0x277/0xa80 net/core/rtnetlink.c:3545
 #1: ffff888052f43d58 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_notifier+0xa4/0x280 net/xdp/xsk.c:1645

stack backtrace:
CPU: 1 UID: 0 PID: 11144 Comm: syz.1.1331 Not tainted 6.16.0-rc3-syzkaller-00042-g78f4e737a53e #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2046
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
 lock_acquire kernel/locking/lockdep.c:5871 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
 xsk_notifier+0x101/0x280 net/xdp/xsk.c:1649
 notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2230
 call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
 call_netdevice_notifiers net/core/dev.c:2282 [inline]
 unregister_netdevice_many_notify+0xf9d/0x2700 net/core/dev.c:12077
 rtnl_delete_link net/core/rtnetlink.c:3511 [inline]
 rtnl_dellink+0x3cb/0xa80 net/core/rtnetlink.c:3553
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6944
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x53d/0x7f0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg net/socket.c:727 [inline]
 ____sys_sendmsg+0xa98/0xc70 net/socket.c:2566
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620
 __sys_sendmsg+0x16d/0x220 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f97c7b8e929
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:00007f97c8abc038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f97c7db5fa0 RCX: 00007f97c7b8e929
RDX: 0000000000000000 RSI: 0000200000000040 RDI: 0000000000000003
RBP: 00007f97c7c10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f97c7db5fa0 R15: 00007fff09d1ae48
 </TASK>
batman_adv: batadv0: Removing interface: batadv_slave_1


---
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