syzbot

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refcount_t: underflow; use-after-free.
WARNING: CPU: 2 PID: 1091 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 2 PID: 1091 Comm: kworker/u32:8 Not tainted 6.10.0-rc3-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 d8 09 0f fd 84 db 0f 85 66 ff ff ff e8 2b 0f 0f fd c6 05 e7 c8 4c 0b 01 90 48 c7 c7 a0 65 8f 8b e8 37 90 d1 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 08 0f 0f fd 0f b6 1d c2 c8 4c 0b 31
RSP: 0018:ffffc900070a79d0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff81511289
RDX: ffff888020754880 RSI: ffffffff81511296 RDI: 0000000000000001
RBP: ffffe8ffad25d2b4 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000003 R12: ffffe8ffad25d2b4
R13: 00000000ffff8880 R14: 0000000000000001 R15: ffffe8ffad25d1d0
FS:  0000000000000000(0000) GS:ffff88802c200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005622c2386000 CR3: 0000000064772000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:275 [inline]
 __refcount_dec_and_test include/linux/refcount.h:307 [inline]
 refcount_dec_and_test include/linux/refcount.h:325 [inline]
 skb_unref include/linux/skbuff.h:1224 [inline]
 __kfree_skb_reason net/core/skbuff.c:1195 [inline]
 kfree_skb_reason+0x1e8/0x210 net/core/skbuff.c:1222
 kfree_skb include/linux/skbuff.h:1257 [inline]
 flush_gro_hash net/core/dev.c:6683 [inline]
 __netif_napi_del net/core/dev.c:6698 [inline]
 __netif_napi_del+0x311/0x570 net/core/dev.c:6689
 gro_cells_destroy net/core/gro_cells.c:117 [inline]
 gro_cells_destroy+0x10a/0x4d0 net/core/gro_cells.c:106
 ip_tunnel_dev_free+0x19/0x60 net/ipv4/ip_tunnel.c:1100
 netdev_run_todo+0x775/0x1250 net/core/dev.c:10693
 cleanup_net+0x591/0xbf0 net/core/net_namespace.c:636
 process_one_work+0x958/0x1ad0 kernel/workqueue.c:3231
 process_scheduled_works kernel/workqueue.c:3312 [inline]
 worker_thread+0x6c8/0xf70 kernel/workqueue.c:3393
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>