linux-kernel - [syzbot] [netfilter?] WARNING: refcount bug in nf_nat_masq

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Message-ID: <6847e69b.a70a0220.27c366.005e.GAE@google.com>
Date: Tue, 10 Jun 2025 01:02:35 -0700
From: syzbot <syzbot+e178f373ec62758ea18b@...kaller.appspotmail.com>
To: coreteam@...filter.org, davem@...emloft.net, edumazet@...gle.com, 
	horms@...nel.org, kadlec@...filter.org, kuba@...nel.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	netfilter-devel@...r.kernel.org, pabeni@...hat.com, pablo@...filter.org, 
	syzkaller-bugs@...glegroups.com
Subject: [syzbot] [netfilter?] WARNING: refcount bug in nf_nat_masq_schedule

Hello,

syzbot found the following issue on:

HEAD commit:    c89756bcf406 Merge tag 'pm-6.16-rc1' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13abfdf4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d2e9181801c1d2a6
dashboard link: https://syzkaller.appspot.com/bug?extid=e178f373ec62758ea18b
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 (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-c89756bc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e43d06e5b003/vmlinux-c89756bc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ae5bc446518d/bzImage-c89756bc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e178f373ec62758ea18b@...kaller.appspotmail.com

------------[ cut here ]------------
refcount_t: saturated; leaking memory.
WARNING: CPU: 0 PID: 1150 at lib/refcount.c:19 refcount_warn_saturate+0x10d/0x210 lib/refcount.c:19
Modules linked in:
CPU: 0 UID: 0 PID: 1150 Comm: kworker/u32:8 Not tainted 6.15.0-syzkaller-03478-gc89756bcf406 #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
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x10d/0x210 lib/refcount.c:19
Code: cb 97 0b 31 ff 89 de e8 21 75 e4 fc 84 db 75 a3 e8 38 7a e4 fc c6 05 c5 cb 97 0b 01 90 48 c7 c7 e0 bc f4 8b e8 34 b3 a3 fc 90 <0f> 0b 90 90 eb 83 e8 18 7a e4 fc 0f b6 1d a2 cb 97 0b 31 ff 89 de
RSP: 0018:ffffc9000667f4f8 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817aa8e8
RDX: ffff888029688000 RSI: ffffffff817aa8f5 RDI: 0000000000000001
RBP: ffff888024f5016c R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888024f5016c
R13: ffff888024f50000 R14: 1ffff92000ccfea6 R15: ffffc9000667f5f0
FS:  0000000000000000(0000) GS:ffff8880d69a1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2a109a CR3: 00000000481e5000 CR4: 0000000000352ef0
DR0: 000000000000006d DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_add_not_zero include/linux/refcount.h:187 [inline]
 __refcount_inc_not_zero include/linux/refcount.h:317 [inline]
 refcount_inc_not_zero include/linux/refcount.h:335 [inline]
 maybe_get_net include/net/net_namespace.h:279 [inline]
 nf_nat_masq_schedule.part.0+0x4ef/0x5f0 net/netfilter/nf_nat_masquerade.c:111
 nf_nat_masq_schedule net/netfilter/nf_nat_masquerade.c:108 [inline]
 masq_inet6_event+0x205/0x250 net/netfilter/nf_nat_masquerade.c:295
 notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
 atomic_notifier_call_chain+0x71/0x1c0 kernel/notifier.c:223
 addrconf_ifdown.isra.0+0xe98/0x1a90 net/ipv6/addrconf.c:3982
 addrconf_notify+0x220/0x19e0 net/ipv6/addrconf.c:3780
 notifier_call_chain+0xbc/0x410 kernel/notifier.c:85
 call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2176
 call_netdevice_notifiers_extack net/core/dev.c:2214 [inline]
 call_netdevice_notifiers net/core/dev.c:2228 [inline]
 dev_close_many+0x319/0x630 net/core/dev.c:1731
 unregister_netdevice_many_notify+0x578/0x26f0 net/core/dev.c:11942
 cleanup_net+0x596/0xb30 net/core/net_namespace.c:649
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c5/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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