l2tp_core: tunl 2: sockfd_lookup(fd=5) returned -9
==================================================================
BUG: KASAN: use-after-free in inet_shutdown+0x2c0/0x340 net/ipv4/af_inet.c:816
Read of size 4 at addr ffff8880910eb9c0 by task syz-executor.4/28989

CPU: 1 PID: 28989 Comm: syz-executor.4 Not tainted 4.14.173-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x13e/0x194 lib/dump_stack.c:58
 print_address_description.cold+0x7c/0x1e2 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+0xa9/0x2ae mm/kasan/report.c:393
 inet_shutdown+0x2c0/0x340 net/ipv4/af_inet.c:816
 pppol2tp_session_close+0x99/0xd0 net/l2tp/l2tp_ppp.c:441
 l2tp_tunnel_closeall+0x234/0x370 net/l2tp/l2tp_core.c:1345
 l2tp_udp_encap_destroy+0x8d/0xf0 net/l2tp/l2tp_core.c:1371
 udpv6_destroy_sock+0xa6/0xd0 net/ipv6/udp.c:1444
 sk_common_release+0x64/0x2f0 net/core/sock.c:2989
 inet_release+0xdf/0x1b0 net/ipv4/af_inet.c:425
 inet6_release+0x4c/0x70 net/ipv6/af_inet6.c:450
 __sock_release+0xcd/0x2b0 net/socket.c:602
 sock_close+0x15/0x20 net/socket.c:1139
 __fput+0x25f/0x790 fs/file_table.c:210
 task_work_run+0x113/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1d6/0x220 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+0x4a3/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4163e1
RSP: 002b:00007ffd4fb4d340 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 00000000004163e1
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 0000000000000001 R08: 00ffffffffffffff R09: 00ffffffffffffff
R10: 00007ffd4fb4d420 R11: 0000000000000293 R12: 000000000076c900
R13: 000000000076c900 R14: 00000000001f69c4 R15: 000000000076c0ec

Allocated by task 28990:
 save_stack+0x32/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc mm/kasan/kasan.c:551 [inline]
 kasan_kmalloc+0xbf/0xe0 mm/kasan/kasan.c:529
 kmem_cache_alloc+0x127/0x770 mm/slab.c:3552
 sock_alloc_inode+0x19/0x250 net/socket.c:251
 alloc_inode+0x5d/0x170 fs/inode.c:209
 new_inode_pseudo+0x14/0xe0 fs/inode.c:898
 sock_alloc+0x3c/0x270 net/socket.c:569
 __sock_create+0x89/0x620 net/socket.c:1239
 sock_create net/socket.c:1315 [inline]
 SYSC_socket net/socket.c:1345 [inline]
 SyS_socket+0xd2/0x170 net/socket.c:1325
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 28997:
 save_stack+0x32/0xa0 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]
 kmem_cache_free+0x7c/0x2b0 mm/slab.c:3758
 destroy_inode+0xb9/0x110 fs/inode.c:266
 iput_final fs/inode.c:1523 [inline]
 iput fs/inode.c:1550 [inline]
 iput+0x457/0x8d0 fs/inode.c:1535
 dentry_unlink_inode+0x26e/0x330 fs/dcache.c:387
 __dentry_kill+0x320/0x550 fs/dcache.c:591
 dentry_kill fs/dcache.c:632 [inline]
 dput.part.0+0x578/0x710 fs/dcache.c:847
 dput+0x1b/0x30 fs/dcache.c:811
 __fput+0x445/0x790 fs/file_table.c:228
 task_work_run+0x113/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1d6/0x220 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+0x4a3/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8880910eb9c0
 which belongs to the cache sock_inode_cache of size 992
The buggy address is located 0 bytes inside of
 992-byte region [ffff8880910eb9c0, ffff8880910ebda0)
The buggy address belongs to the page:
page:ffffea0002443ac0 count:1 mapcount:0 mapping:ffff8880910eb0c0 index:0xffff8880910ebffd
flags: 0xfffe0000000100(slab)
raw: 00fffe0000000100 ffff8880910eb0c0 ffff8880910ebffd 0000000100000002
raw: ffffea0002445560 ffffea0002449320 ffff8880a9984900 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880910eb880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880910eb900: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880910eb980: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8880910eba00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880910eba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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