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BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:183 [inline]
BUG: KASAN: use-after-free in atomic_read arch/x86/include/asm/atomic.h:27 [inline]
BUG: KASAN: use-after-free in refcount_inc_not_zero+0xd3/0xe0 lib/refcount.c:120
Read of size 4 at addr ffff888047b98980 by task kworker/u4:7/918

CPU: 0 PID: 918 Comm: kworker/u4:7 Not tainted 4.14.155-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x142/0x197 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report mm/kasan/report.c:409 [inline]
 kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 __read_once_size include/linux/compiler.h:183 [inline]
 atomic_read arch/x86/include/asm/atomic.h:27 [inline]
 refcount_inc_not_zero+0xd3/0xe0 lib/refcount.c:120
 refcount_inc+0x16/0x40 lib/refcount.c:153
 sock_hold include/net/sock.h:619 [inline]
 pppol2tp_session_sock_hold+0x48/0x60 net/l2tp/l2tp_ppp.c:263
 l2tp_tunnel_closeall+0x1ef/0x380 net/l2tp/l2tp_core.c:1332
 l2tp_tunnel_del_work+0x64/0x410 net/l2tp/l2tp_core.c:1380
 process_one_work+0x863/0x1600 kernel/workqueue.c:2114
 worker_thread+0x5d9/0x1050 kernel/workqueue.c:2248
 kthread+0x319/0x430 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Allocated by task 25435:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
 __do_kmalloc mm/slab.c:3720 [inline]
 __kmalloc+0x15d/0x7a0 mm/slab.c:3729
 kmalloc include/linux/slab.h:493 [inline]
 sk_prot_alloc+0x171/0x2a0 net/core/sock.c:1467
 sk_alloc+0x39/0xd70 net/core/sock.c:1521
 pppol2tp_create+0x32/0x1f0 net/l2tp/l2tp_ppp.c:534
 pppox_create+0xf7/0x210 drivers/net/ppp/pppox.c:134
 __sock_create+0x2f6/0x620 net/socket.c:1275
 sock_create net/socket.c:1315 [inline]
 SYSC_socket net/socket.c:1345 [inline]
 SyS_socket+0xd3/0x170 net/socket.c:1325
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 25429:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x45/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xcc/0x270 mm/slab.c:3815
 sk_prot_free net/core/sock.c:1504 [inline]
 __sk_destruct+0x450/0x580 net/core/sock.c:1581
 sk_destruct+0xa4/0xd0 net/core/sock.c:1596
 __sk_free+0x54/0x230 net/core/sock.c:1604
 sk_free+0x35/0x40 net/core/sock.c:1615
 sock_put include/net/sock.h:1653 [inline]
 pppol2tp_release+0x244/0x300 net/l2tp/l2tp_ppp.c:501
 __sock_release+0xce/0x2b0 net/socket.c:602
 sock_close+0x1b/0x30 net/socket.c:1139
 __fput+0x275/0x7a0 fs/file_table.c:210
 ____fput+0x16/0x20 fs/file_table.c:244
 task_work_run+0x114/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff888047b98900
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 128 bytes inside of
 2048-byte region [ffff888047b98900, ffff888047b99100)
The buggy address belongs to the page:
page:ffffea00011ee600 count:1 mapcount:0 mapping:ffff888047b98080 index:0x0 compound_mapcount: 0
flags: 0x1fffc0000008100(slab|head)
raw: 01fffc0000008100 ffff888047b98080 0000000000000000 0000000100000003
raw: ffffea00012ab120 ffffea00029782a0 ffff8880aa800c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888047b98880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888047b98900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888047b98980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888047b98a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888047b98a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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