possible deadlock in xsk_diag_dump (2)

Status: fixed on 2025/10/09 01:15
Subsystems: net bpf
[Documentation on labels]
Reported-by: syzbot+e6300f66a999a6612477@syzkaller.appspotmail.com
Fix commit: c64237960819 hamradio: ignore ops-locked netdevs
First crash: 372d, last: 372d
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH net 1/2] net: lapbether: ignore ops-locked netdevs 3 (3) 2025/08/08 20:50
[syzbot] [bpf?] [net?] possible deadlock in xsk_diag_dump (2) 1 (2) 2025/08/05 17:16
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in xsk_diag_dump net bpf 4 4 484d 490d 28/29 fixed on 2025/06/10 16:19

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller-11489-gd2eedaa3909b #0 Not tainted
------------------------------------------------------
syz.8.4735/22857 is trying to acquire lock:
ffff8880223e06b8 (&xs->mutex){+.+.}-{4:4}, at: xsk_diag_fill net/xdp/xsk_diag.c:113 [inline]
ffff8880223e06b8 (&xs->mutex){+.+.}-{4:4}, at: xsk_diag_dump+0x550/0x14d0 net/xdp/xsk_diag.c:166

but task is already holding lock:
ffff888031291c98 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_diag_dump+0x178/0x14d0 net/xdp/xsk_diag.c:158

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&net->xdp.lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760
       xsk_notifier+0x89/0x230 net/xdp/xsk.c:1664
       notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       unregister_netdevice_many_notify+0x14d7/0x1ff0 net/core/dev.c:12156
       unregister_netdevice_many net/core/dev.c:12219 [inline]
       unregister_netdevice_queue+0x33c/0x380 net/core/dev.c:12063
       register_netdevice+0x1689/0x1ae0 net/core/dev.c:11241
       bpq_new_device drivers/net/hamradio/bpqether.c:481 [inline]
       bpq_device_event+0x491/0x600 drivers/net/hamradio/bpqether.c:523
       notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9608
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       devinet_ioctl+0xbb4/0x1b50 net/ipv4/devinet.c:1200
       inet_ioctl+0x3c0/0x4c0 net/ipv4/af_inet.c:1001
       sock_do_ioctl+0xdc/0x300 net/socket.c:1238
       sock_ioctl+0x576/0x790 net/socket.c:1359
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&dev_instance_lock_key#20){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760
       netdev_lock include/linux/netdevice.h:2758 [inline]
       netdev_lock_ops include/net/netdev_lock.h:42 [inline]
       xsk_bind+0x2f7/0xf90 net/xdp/xsk.c:1193
       __sys_bind_socket net/socket.c:1858 [inline]
       __sys_bind+0x2c6/0x3e0 net/socket.c:1889
       __do_sys_bind net/socket.c:1894 [inline]
       __se_sys_bind net/socket.c:1892 [inline]
       __x64_sys_bind+0x7a/0x90 net/socket.c:1892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760
       xsk_diag_fill net/xdp/xsk_diag.c:113 [inline]
       xsk_diag_dump+0x550/0x14d0 net/xdp/xsk_diag.c:166
       netlink_dump+0x6e4/0xe90 net/netlink/af_netlink.c:2327
       __netlink_dump_start+0x5cb/0x7e0 net/netlink/af_netlink.c:2442
       netlink_dump_start include/linux/netlink.h:341 [inline]
       xsk_diag_handler_dump+0x183/0x220 net/xdp/xsk_diag.c:193
       sock_diag_rcv_msg+0x4cc/0x600 net/core/sock_diag.c:-1
       netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
       netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
       netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:729
       sock_write_iter+0x258/0x330 net/socket.c:1179
       do_iter_readv_writev+0x56e/0x7f0 fs/read_write.c:-1
       vfs_writev+0x31a/0x960 fs/read_write.c:1057
       do_writev+0x14d/0x2d0 fs/read_write.c:1103
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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.8.4735/22857:
 #0: ffff8880223e16d0 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{4:4}, at: __netlink_dump_start+0xfe/0x7e0 net/netlink/af_netlink.c:2406
 #1: ffff888031291c98 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_diag_dump+0x178/0x14d0 net/xdp/xsk_diag.c:158

stack backtrace:
CPU: 0 UID: 0 PID: 22857 Comm: syz.8.4735 Not tainted 6.16.0-syzkaller-11489-gd2eedaa3909b #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x187/0x1360 kernel/locking/mutex.c:760
 xsk_diag_fill net/xdp/xsk_diag.c:113 [inline]
 xsk_diag_dump+0x550/0x14d0 net/xdp/xsk_diag.c:166
 netlink_dump+0x6e4/0xe90 net/netlink/af_netlink.c:2327
 __netlink_dump_start+0x5cb/0x7e0 net/netlink/af_netlink.c:2442
 netlink_dump_start include/linux/netlink.h:341 [inline]
 xsk_diag_handler_dump+0x183/0x220 net/xdp/xsk_diag.c:193
 sock_diag_rcv_msg+0x4cc/0x600 net/core/sock_diag.c:-1
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 sock_write_iter+0x258/0x330 net/socket.c:1179
 do_iter_readv_writev+0x56e/0x7f0 fs/read_write.c:-1
 vfs_writev+0x31a/0x960 fs/read_write.c:1057
 do_writev+0x14d/0x2d0 fs/read_write.c:1103
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6e7b38eb69
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:00007f6e791d5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f6e7b5b6160 RCX: 00007f6e7b38eb69
RDX: 0000000000000001 RSI: 0000200000000140 RDI: 0000000000000007
RBP: 00007f6e7b411df1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f6e7b5b6160 R15: 00007ffdbe0ab9a8
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/04 13:29 upstream d2eedaa3909b 7368264b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in xsk_diag_dump
* Struck through repros no longer work on HEAD.