syzbot

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refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 8 at lib/refcount.c:28 refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 8 Comm: kworker/u4:0 Not tainted 5.15.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Code: e9 db fe ff ff 48 89 df e8 9c b2 e3 fd e9 8a fe ff ff e8 72 5a 9c fd 48 c7 c7 a0 ee e3 89 c6 05 19 8a 7f 09 01 e8 db 6e 19 05 <0f> 0b e9 af fe ff ff 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55
RSP: 0018:ffffc90000cd7958 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888011ebd580 RSI: ffffffff815e8da8 RDI: fffff5200019af1d
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815e2b4e R11: 0000000000000000 R12: ffffe8ffffc9621d
R13: dffffc0000000000 R14: 0000000000000007 R15: ffffe8ffffc96141
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055ddc90bb160 CR3: 00000000733c8000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 skb_unref include/linux/skbuff.h:1068 [inline]
 skb_unref include/linux/skbuff.h:1062 [inline]
 kfree_skb+0x326/0x3f0 net/core/skbuff.c:770
 flush_gro_hash net/core/dev.c:6954 [inline]
 __netif_napi_del.part.0+0x2c6/0x520 net/core/dev.c:6969
 __netif_napi_del+0x3c/0x50 net/core/dev.c:6962
 gro_cells_destroy net/core/gro_cells.c:102 [inline]
 gro_cells_destroy+0x115/0x360 net/core/gro_cells.c:92
 ip6_dev_free+0x15/0x60 net/ipv6/ip6_tunnel.c:248
 netdev_run_todo+0x6b4/0xa80 net/core/dev.c:10600
 ip6_tnl_exit_batch_net+0x5fa/0x890 net/ipv6/ip6_tunnel.c:2312
 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:171
 cleanup_net+0x4ea/0xb00 net/core/net_namespace.c:591
 process_one_work+0x9bf/0x16b0 kernel/workqueue.c:2297
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295