syzbot

==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x24/0x4e0 net/l2tp/l2tp_core.c:1563
Write of size 8 at addr ffff8881246b6808 by task kworker/u4:3/311

CPU: 1 PID: 311 Comm: kworker/u4:3 Not tainted 5.10.225-syzkaller-00513-g8d23314f588a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack_lvl+0x1e2/0x24b lib/dump_stack.c:118
 print_address_description+0x81/0x3b0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x179/0x1c0 mm/kasan/report.c:452
 kasan_check_range+0x293/0x2a0 mm/kasan/generic.c:189
 __kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
 l2tp_session_delete+0x24/0x4e0 net/l2tp/l2tp_core.c:1563
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
 l2tp_tunnel_del_work+0x19d/0x380 net/l2tp/l2tp_core.c:1258
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Allocated by task 1605:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 ____kasan_kmalloc+0xdb/0x110 mm/kasan/common.c:509
 __kasan_kmalloc+0x9/0x10 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 __kmalloc+0x1aa/0x330 mm/slub.c:4033
 kmalloc include/linux/slab.h:557 [inline]
 kzalloc include/linux/slab.h:664 [inline]
 l2tp_session_create+0x38/0xb60 net/l2tp/l2tp_core.c:1599
 pppol2tp_connect+0xc5d/0x1690 net/l2tp/l2tp_ppp.c:782
 __sys_connect_file net/socket.c:1866 [inline]
 __sys_connect+0x388/0x410 net/socket.c:1883
 __do_sys_connect net/socket.c:1893 [inline]
 __se_sys_connect net/socket.c:1890 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1890
 do_syscall_64+0x34/0x70
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 1594:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x121/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1595 [inline]
 slab_free_freelist_hook+0xc0/0x190 mm/slub.c:1621
 slab_free mm/slub.c:3203 [inline]
 kfree+0xc3/0x270 mm/slub.c:4191
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_dec_refcount+0xac/0x1b0 net/l2tp/l2tp_core.c:205
 pppol2tp_session_destruct+0xaf/0xf0 net/l2tp/l2tp_ppp.c:419
 __sk_destruct+0x59/0x620 net/core/sock.c:1813
 sk_destruct net/core/sock.c:1858 [inline]
 __sk_free+0x36c/0x470 net/core/sock.c:1869
 sk_free+0x51/0x80 net/core/sock.c:1880
 sock_put include/net/sock.h:1850 [inline]
 pppol2tp_put_sk+0x77/0xb0 net/l2tp/l2tp_ppp.c:402
 rcu_do_batch+0x597/0xc40 kernel/rcu/tree.c:2494
 rcu_core+0x5ad/0xe40 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x268/0x5bb kernel/softirq.c:309

Last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd3/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu kernel/rcu/tree.c:2976 [inline]
 call_rcu+0x135/0x11f0 kernel/rcu/tree.c:3050
 pppol2tp_release+0x20f/0x2d0 net/l2tp/l2tp_ppp.c:458
 __sock_release net/socket.c:597 [inline]
 sock_close+0xdf/0x270 net/socket.c:1286
 __fput+0x33d/0x7b0 fs/file_table.c:281
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x129/0x190 kernel/task_work.c:189
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop+0xbf/0xd0 kernel/entry/common.c:172
 exit_to_user_mode_prepare kernel/entry/common.c:199 [inline]
 syscall_exit_to_user_mode+0xa2/0x1a0 kernel/entry/common.c:274
 do_syscall_64+0x40/0x70 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Second to last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd3/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 kvfree_call_rcu+0x136/0x650 kernel/rcu/tree.c:3535
 neigh_destroy+0x3f9/0x510 net/core/neighbour.c:865
 neigh_release include/net/neighbour.h:427 [inline]
 neigh_cleanup_and_release+0x73/0x1b0 net/core/neighbour.c:104
 neigh_flush_dev+0x65e/0x840 net/core/neighbour.c:375
 __neigh_ifdown+0x41/0x3a0 net/core/neighbour.c:392
 neigh_ifdown+0x1f/0x30 net/core/neighbour.c:409
 rt6_disable_ip+0x69a/0x720 net/ipv6/route.c:4794
 addrconf_ifdown+0x160/0x1a60 net/ipv6/addrconf.c:3784
 addrconf_notify+0x378/0xe90
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x8c/0xf0 kernel/notifier.c:410
 call_netdevice_notifiers_info net/core/dev.c:2054 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2066 [inline]
 call_netdevice_notifiers net/core/dev.c:2080 [inline]
 dev_close_many+0x37f/0x530 net/core/dev.c:1655
 unregister_netdevice_many+0x492/0x17d0 net/core/dev.c:10724
 default_device_exit_batch+0x38a/0x3f0 net/core/dev.c:11267
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x6e9/0xcb0 net/core/net_namespace.c:609
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

The buggy address belongs to the object at ffff8881246b6800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
 512-byte region [ffff8881246b6800, ffff8881246b6a00)
The buggy address belongs to the page:
page:ffffea000491ad00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1246b4
head:ffffea000491ad00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 312, ts 25537963954, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x166/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2d8c/0x2f30 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x435/0xaf0 mm/page_alloc.c:5348
 allocate_slab mm/slub.c:1808 [inline]
 new_slab+0x80/0x400 mm/slub.c:1869
 new_slab_objects mm/slub.c:2627 [inline]
 ___slab_alloc+0x302/0x4b0 mm/slub.c:2791
 __slab_alloc+0x63/0xa0 mm/slub.c:2831
 slab_alloc_node mm/slub.c:2913 [inline]
 slab_alloc mm/slub.c:2955 [inline]
 __kmalloc_track_caller+0x1f8/0x320 mm/slub.c:4536
 __kmalloc_reserve net/core/skbuff.c:144 [inline]
 __alloc_skb+0xbc/0x510 net/core/skbuff.c:212
 alloc_skb include/linux/skbuff.h:1126 [inline]
 ndisc_alloc_skb+0xf3/0x2d0 net/ipv6/ndisc.c:423
 ndisc_send_ns+0x29d/0x830 net/ipv6/ndisc.c:629
 addrconf_dad_work+0xb9b/0x1700 net/ipv6/addrconf.c:4206
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881246b6700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881246b6780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881246b6800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8881246b6880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881246b6900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 311 at lib/refcount.c:28 refcount_warn_saturate+0x158/0x1a0 lib/refcount.c:28
Modules linked in:

CPU: 1 PID: 311 Comm: kworker/u4:3 Tainted: G    B             5.10.225-syzkaller-00513-g8d23314f588a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: l2tp l2tp_tunnel_del_work

RIP: 0010:refcount_warn_saturate+0x158/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 c0 0d 60 85 e8 b4 cf ea fe 0f 0b eb 8b e8 9b 49 17 ff c6 05 67 6b 8d 04 01 48 c7 c7 20 0e 60 85 e8 98 cf ea fe <0f> 0b e9 6c ff ff ff e8 7c 49 17 ff c6 05 49 6b 8d 04 01 48 c7 c7
RSP: 0018:ffffc90005777c40 EFLAGS: 00010246
RAX: 08c7544b9f57dd00 RBX: 0000000000000003 RCX: ffff888122da93c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90005777c50 R08: ffffffff81522098 R09: 0000000000000003
R10: fffff52000aeeec4 R11: dffffc0000000001 R12: ffff88810a7c5c20
R13: ffff88810a7c5c00 R14: 0000000000000003 R15: ffff8881246b6888
FS:  0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fadf0ad3000 CR3: 000000011edd8000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
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]
 l2tp_session_dec_refcount+0xc7/0x1b0 net/l2tp/l2tp_core.c:204
 l2tp_session_delete+0x3bc/0x4e0 net/l2tp/l2tp_core.c:1572
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
 l2tp_tunnel_del_work+0x19d/0x380 net/l2tp/l2tp_core.c:1258
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
---[ end trace ea3a80f46a35887c ]---