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BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:186 [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 ffff888056f51080 by task syz-executor.3/24060

CPU: 1 PID: 24060 Comm: syz-executor.3 Not tainted 4.14.114 #4
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+0x138/0x19c lib/dump_stack.c:53
 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+0xaf/0x2b5 mm/kasan/report.c:393
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 __read_once_size include/linux/compiler.h:186 [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]
 l2tp_session_add_to_tunnel net/l2tp/l2tp_core.c:368 [inline]
 l2tp_session_create+0x118b/0x1600 net/l2tp/l2tp_core.c:1846
 pppol2tp_connect+0x11c5/0x18b0 net/l2tp/l2tp_ppp.c:721
 SYSC_connect+0x1f8/0x2d0 net/socket.c:1655
 SyS_connect+0x24/0x30 net/socket.c:1636
 do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x458da9
RSP: 002b:00007ff9e6d7dc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458da9
RDX: 000000000000002e RSI: 00000000200000c0 RDI: 0000000000000006
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff9e6d7e6d4
R13: 00000000004bf20b R14: 00000000004d02f0 R15: 00000000ffffffff

Allocated by task 23630:
 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
 kasan_slab_alloc+0xf/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x780 mm/slab.c:3552
 sk_prot_alloc+0x67/0x2a0 net/core/sock.c:1464
 sk_alloc+0x39/0xd70 net/core/sock.c:1524
 inet6_create net/ipv6/af_inet6.c:183 [inline]
 inet6_create+0x2d8/0xe20 net/ipv6/af_inet6.c:110
 __sock_create+0x2fb/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+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 23624:
 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]
 kmem_cache_free+0x83/0x2b0 mm/slab.c:3758
 sk_prot_free net/core/sock.c:1505 [inline]
 __sk_destruct+0x3df/0x5d0 net/core/sock.c:1586
 sk_destruct+0x67/0x80 net/core/sock.c:1594
 __sk_free+0x54/0x230 net/core/sock.c:1602
 sk_free+0x35/0x40 net/core/sock.c:1613
 sock_put include/net/sock.h:1653 [inline]
 l2tp_session_free+0x1b2/0x210 net/l2tp/l2tp_core.c:1709
 l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:300 [inline]
 pppol2tp_session_destruct+0xd8/0x110 net/l2tp/l2tp_ppp.c:460
 __sk_destruct+0x51/0x5d0 net/core/sock.c:1559
 sk_destruct+0x67/0x80 net/core/sock.c:1594
 __sk_free+0x54/0x230 net/core/sock.c:1602
 sk_free+0x35/0x40 net/core/sock.c:1613
 sock_put include/net/sock.h:1653 [inline]
 pppol2tp_release+0x244/0x300 net/l2tp/l2tp_ppp.c:501
 __sock_release+0xd3/0x2c0 net/socket.c:602
 sock_close+0x1b/0x30 net/socket.c:1139
 __fput+0x277/0x7a0 fs/file_table.c:210
 ____fput+0x16/0x20 fs/file_table.c:244
 task_work_run+0x119/0x190 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:163
 prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:267 [inline]
 do_syscall_64+0x4a9/0x630 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff888056f51000
 which belongs to the cache UDPv6 of size 1728
The buggy address is located 128 bytes inside of
 1728-byte region [ffff888056f51000, ffff888056f516c0)
The buggy address belongs to the page:
page:ffffea00015bd440 count:1 mapcount:0 mapping:ffff888056f51000 index:0x0
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff888056f51000 0000000000000000 0000000100000002
raw: ffffea0001817ca0 ffffea00017992e0 ffff888216648dc0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888056f50f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888056f51000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888056f51080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888056f51100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888056f51180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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