[syzbot] [net?] WARNING: refcount bug in gro_cleanup

[syzbot <syzbot+9de2587cce48f5642f16@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    d0c22de9995b Merge tag 'input-for-v6.15-rc7' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1745b5f4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9fd1c9848687d742
dashboard link: https://syzkaller.appspot.com/bug?extid=9de2587cce48f5642f16
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b862906e9f4b/disk-d0c22de9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c0d716f15db2/vmlinux-d0c22de9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7ffe8e4af4ec/bzImage-d0c22de9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9de2587cce48f5642f16@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 8170 at lib/refcount.c:28 refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Modules linked in:
CPU: 1 UID: 0 PID: 8170 Comm: syz.4.605 Not tainted 6.15.0-rc7-syzkaller-00152-gd0c22de9995b #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:refcount_warn_saturate+0x11a/0x1d0 lib/refcount.c:28
Code: 80 aa c1 8b e8 e7 52 cb fc 90 0f 0b 90 90 eb d7 e8 4b f6 06 fd c6 05 67 3c b0 0a 01 90 48 c7 c7 e0 aa c1 8b e8 c7 52 cb fc 90 <0f> 0b 90 90 eb b7 e8 2b f6 06 fd c6 05 44 3c b0 0a 01 90 48 c7 c7
RSP: 0018:ffffc9000419f628 EFLAGS: 00010246
RAX: b3f3c577eef85a00 RBX: 0000000000000003 RCX: 0000000000080000
RDX: ffffc9001071e000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: 0000000000000000 R08: ffffffff8f7f3577 R09: 1ffffffff1efe6ae
R10: dffffc0000000000 R11: fffffbfff1efe6af R12: dffffc0000000000
R13: 4888ffffe8ffffc8 R14: ffffe8ffffc8496e R15: ffffe8ffffc8488a
FS:  00007f92701cb6c0(0000) GS:ffff8881261c2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0f5af71440 CR3: 00000000262e0000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 kfree_skb_reason include/linux/skbuff.h:1279 [inline]
 kfree_skb include/linux/skbuff.h:1288 [inline]
 gro_cleanup+0x300/0x640 net/core/gro.c:815
 __netif_napi_del_locked+0x2e0/0x3c0 net/core/dev.c:7301
 __netif_napi_del include/linux/netdevice.h:2876 [inline]
 gro_cells_destroy+0x16a/0x430 net/core/gro_cells.c:117
 ip_tunnel_dev_free+0x19/0x30 net/ipv4/ip_tunnel.c:1102
 netdev_run_todo+0xcd7/0xea0 net/core/dev.c:11300
 setup_net+0x5db/0x830 net/core/net_namespace.c:392
 copy_net_ns+0x32e/0x590 net/core/net_namespace.c:518
 create_new_namespaces+0x3d3/0x700 kernel/nsproxy.c:110
 copy_namespaces+0x438/0x4b0 kernel/nsproxy.c:179
 copy_process+0x1700/0x3b80 kernel/fork.c:2433
 kernel_clone+0x21e/0x870 kernel/fork.c:2845
 __do_sys_clone kernel/fork.c:2988 [inline]
 __se_sys_clone kernel/fork.c:2972 [inline]
 __x64_sys_clone+0x18b/0x1e0 kernel/fork.c:2972
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f926f38e969
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:00007f92701cafe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f926f5b6160 RCX: 00007f926f38e969
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000042000000
RBP: 00007f926f410ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f926f5b6160 R15: 00007fff8df30f78
 </TASK>


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