Re: [moderation/CI] Re: net: Support per-netns device unregistration

#syz upstream


On Thu, Jul 2, 2026 at 9:08 AM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v1] net: Support per-netns device unregistration
> https://lore.kernel.org/all/[email protected]
> * [PATCH v1 net-next 01/14] rtnetlink: Lock sock_net(skb->sk) in rtnl_newlink().
> * [PATCH v1 net-next 02/14] rtnetlink: Call unregister_netdevice_many() only once in rtnl_link_unregister().
> * [PATCH v1 net-next 03/14] rtnetlink: Add per-netns rtnl_work.
> * [PATCH v1 net-next 04/14] net: Wrap default_device_exit_net() with __rtnl_net_lock().
> * [PATCH v1 net-next 05/14] net: Hold __rtnl_net_lock() in netdev_wait_allrefs_any().
> * [PATCH v1 net-next 06/14] net: Add per-netns netdev unregistration infra.
> * [PATCH v1 net-next 07/14] net: Call unregister_netdevice_many() per netns.
> * [PATCH v1 net-next 08/14] veth: Support per-netns device unregistration.
> * [PATCH v1 net-next 09/14] bareudp: Protect bareudp_list with mutex.
> * [PATCH v1 net-next 10/14] bareudp: Support per-netns netdev unregistration.
> * [PATCH v1 net-next 11/14] ipvlan: Convert ipvl_port.count to refcount_t.
> * [PATCH v1 net-next 12/14] ipvlan: Synchronise ipvlan_init() and ipvlan_uninit() for the same lower dev.
> * [PATCH v1 net-next 13/14] ipvlan: Protect ipvl_port.ipvlans with mutex.
> * [PATCH v1 net-next 14/14] ipvlan: Support per-netns netdev unregistration.
>
> and found the following issue:
> possible deadlock in __dev_change_net_namespace
>
> Full report is available here:
> https://ci.syzbot.org/series/a744b257-d741-4780-8a53-f156b2a7afc9
>
> ***
>
> possible deadlock in __dev_change_net_namespace
>
> tree:      net-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
> base:      d6e81529749190123aa0040626c7e5dbc20fdc9a
> arch:      amd64
> compiler:  Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
> config:    https://ci.syzbot.org/builds/243cd0ec-28f9-4d21-8f16-3d2fbad8388d/config
> syz repro: https://ci.syzbot.org/findings/a8a0740d-fdec-4a20-9aa5-7cb955707913/syz_repro
>
> veth0_macvtap: left promiscuous mode
> ============================================
> WARNING: possible recursive locking detected
> syzkaller #0 Not tainted
> --------------------------------------------
> syz.1.18/5814 is trying to acquire lock:
> ffffffff9a9b0418 (&net->dev_unreg_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
> ffffffff9a9b0418 (&net->dev_unreg_lock){+.+.}-{3:3}, at: unregister_netdevice_move_net net/core/dev.c:-1 [inline]
> ffffffff9a9b0418 (&net->dev_unreg_lock){+.+.}-{3:3}, at: __dev_change_net_namespace+0x1479/0x2200 net/core/dev.c:12768
>
> but task is already holding lock:
> ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
> ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: unregister_netdevice_move_net net/core/dev.c:-1 [inline]
> ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: __dev_change_net_namespace+0x146a/0x2200 net/core/dev.c:12768
>
> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(&net->dev_unreg_lock);
>   lock(&net->dev_unreg_lock);
>
>  *** DEADLOCK ***
>
>  May be due to missing lock nesting notation
>
> 4 locks held by syz.1.18/5814:
>  #0: ffffffff8fdeb0c0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
>  #0: ffffffff8fdeb0c0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock+0x2a/0x2b0 net/core/rtnetlink.c:366
>  #1: ffffffff9a9b0380 (&net->rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock+0x76/0x2b0 net/core/rtnetlink.c:369
>  #2: ffff88810b6cf840 (&net->rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock+0xbf/0x2b0 net/core/rtnetlink.c:369
>  #3: ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
>  #3: ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: unregister_netdevice_move_net net/core/dev.c:-1 [inline]
>  #3: ffff88810b6cf8d8 (&net->dev_unreg_lock){+.+.}-{3:3}, at: __dev_change_net_namespace+0x146a/0x2200 net/core/dev.c:12768
>
> stack backtrace:
> CPU: 0 UID: 0 PID: 5814 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>  print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
>  check_deadlock kernel/locking/lockdep.c:3093 [inline]
>  validate_chain kernel/locking/lockdep.c:3895 [inline]
>  __lock_acquire+0x24df/0x2cf0 kernel/locking/lockdep.c:5237
>  lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
>  __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
>  _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
>  spin_lock include/linux/spinlock.h:342 [inline]
>  unregister_netdevice_move_net net/core/dev.c:-1 [inline]
>  __dev_change_net_namespace+0x1479/0x2200 net/core/dev.c:12768
>  do_setlink+0x2d1/0x4670 net/core/rtnetlink.c:3148
>  rtnl_changelink net/core/rtnetlink.c:3880 [inline]
>  __rtnl_newlink net/core/rtnetlink.c:4053 [inline]
>  rtnl_newlink+0x1612/0x1b50 net/core/rtnetlink.c:4192
>  rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7109
>  netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
>  netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>  netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
>  netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
>  sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
>  __sock_sendmsg net/socket.c:790 [inline]
>  ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
>  ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
>  __sys_sendmsg net/socket.c:2770 [inline]
>  __do_sys_sendmsg net/socket.c:2775 [inline]
>  __se_sys_sendmsg net/socket.c:2773 [inline]
>  __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fbdc639ce59
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fbdc59fe028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007fbdc6615fa0 RCX: 00007fbdc639ce59
> RDX: 0000000000000000 RSI: 0000200000000740 RDI: 0000000000000003
> RBP: 00007fbdc6432e6f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fbdc6616038 R14: 00007fbdc6615fa0 R15: 00007ffd94dcb1f8
>  </TASK>
> syz.1.18 (5814) used greatest stack depth: 19864 bytes left
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: [email protected]
>
> ---
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>
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-- 
Ⲡⲟⲓⲙⲏⲛ Ⲅⲉⲱⲣⲅⲓⲟⲥ - Pimyn Girgis
Software Engineer
Kernel Dynamic Analysis
[email protected]