==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8801d8ae6280 by task syz-executor091/5434

CPU: 1 PID: 5434 Comm: syz-executor091 Not tainted 4.4.138-g226f96b #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 3e237e3ca7d753a9 ffff8800ac04fb50 ffffffff81e0ed0d
 ffffea000762b980 ffff8801d8ae6280 0000000000000000 ffff8801d8ae6280
 ffffffff82f1a2b0 ffff8800ac04fb88 ffffffff81515a16 ffff8801d8ae6280
Call Trace:
 [<ffffffff81e0ed0d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0ed0d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81515a16>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff81515d35>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff81515d35>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814f9804>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8359ad34>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff835a786f>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82f1a186>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f1a2c6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522e05>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81523345>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bd7f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff81135285>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff81135285>] do_exit+0x9e5/0x26b0 kernel/exit.c:759
 [<ffffffff8113b1d1>] do_group_exit+0x111/0x330 kernel/exit.c:889
 [<ffffffff8113b40d>] SYSC_exit_group kernel/exit.c:900 [inline]
 [<ffffffff8113b40d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:898
 [<ffffffff838c2725>] entry_SYSCALL_64_fastpath+0x22/0x9e

Allocated by task 5432:
 [<ffffffff81033e46>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f88d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8bb7>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8bb7>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f52d4>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff835a0179>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff835a0179>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff835a0179>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835a4e80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1eba8>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f214e4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c2725>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 5399:
 [<ffffffff81033e46>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f88d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f9202>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f9202>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f6704>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f6704>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f6704>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f6704>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff8359d0e0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff8359f499>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8359f499>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff8359ffab>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff83492431>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f2fa5d>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff834910e5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff832f8bef>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff8341b810>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f1a186>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f1a2c6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522e05>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81523345>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bd7f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff81135285>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff81135285>] do_exit+0x9e5/0x26b0 kernel/exit.c:759
 [<ffffffff8113b1d1>] do_group_exit+0x111/0x330 kernel/exit.c:889
 [<ffffffff8113b40d>] SYSC_exit_group kernel/exit.c:900 [inline]
 [<ffffffff8113b40d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:898
 [<ffffffff838c2725>] entry_SYSCALL_64_fastpath+0x22/0x9e

The buggy address belongs to the object at ffff8801d8ae6280
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801d8ae6280, ffff8801d8ae6480)
The buggy address belongs to the page:
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 1 Comm: init Not tainted 4.4.138-g226f96b #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d99a8000 task.stack: ffff8801d99b0000
RIP: 0010:[<ffffffff81e6f9ff>]  [<ffffffff81e6f9ff>] __hlist_del include/linux/list.h:621 [inline]
RIP: 0010:[<ffffffff81e6f9ff>]  [<ffffffff81e6f9ff>] hlist_del include/linux/list.h:626 [inline]
RIP: 0010:[<ffffffff81e6f9ff>]  [<ffffffff81e6f9ff>] alloc_object lib/debugobjects.c:146 [inline]
RIP: 0010:[<ffffffff81e6f9ff>]  [<ffffffff81e6f9ff>] __debug_object_init+0x2df/0xa90 lib/debugobjects.c:320
RSP: 0018:ffff8801d99b7950  EFLAGS: 00010806
RAX: ffffffff85992760 RBX: ffff8800ab610ed0 RCX: 0000000000000000
RDX: ffffea000762b980 RSI: ffffea000762b988 RDI: 8000000000004088
RBP: ffff8801d99b7a18 R08: ffffea000762b990 R09: dffffc0000000000
R10: 1000000000000811 R11: ffff8801d99a8000 R12: 1ffff1003b336f32
R13: ffffffff859f6960 R14: 8000000000004080 R15: 00000000000641c0
FS:  00007fa61863c7a0(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa617fc6834 CR3: 00000000b6567000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d99a88b8 0000000000000000 ffff8801d99b7a20 0000000000000046
 ffff880100000000 0000000000000296 ffffffff859f6968 ffffffff844bdb00
 0000000041b58ab3 ffffffff842092c4 ffffffff81e6f720 0000000000000000
Call Trace:
 [<ffffffff81e701c6>] debug_object_init+0x16/0x20 lib/debugobjects.c:364
 [<ffffffff8127791f>] rcuhead_fixup_activate+0x1f/0x40 kernel/rcu/update.c:381
 [<ffffffff81e70428>] debug_object_fixup lib/debugobjects.c:279 [inline]
 [<ffffffff81e70428>] debug_object_activate+0x238/0x480 lib/debugobjects.c:439
 [<ffffffff812848f5>] debug_rcu_head_queue kernel/rcu/rcu.h:75 [inline]
 [<ffffffff812848f5>] __call_rcu.constprop.66+0x35/0x930 kernel/rcu/tree.c:3059
 [<ffffffff81285202>] call_rcu+0x12/0x20 kernel/rcu/tree_plugin.h:662
 [<ffffffff81562067>] dentry_free+0xb7/0x150 fs/dcache.c:335
 [<ffffffff8156424c>] __dentry_kill+0x4ac/0x5f0 fs/dcache.c:576
 [<ffffffff81567a6e>] dentry_kill fs/dcache.c:603 [inline]
 [<ffffffff81567a6e>] dput.part.26+0x4ce/0x760 fs/dcache.c:818
 [<ffffffff81567d1f>] dput+0x1f/0x30 fs/dcache.c:782
 [<ffffffff81542e7e>] path_put fs/namei.c:506 [inline]
 [<ffffffff81542e7e>] terminate_walk+0x1ae/0x450 fs/namei.c:625
 [<ffffffff8154bacb>] path_lookupat.isra.36+0x1cb/0x410 fs/namei.c:2172
 [<ffffffff81550657>] filename_lookup.part.53+0x177/0x370 fs/namei.c:2188
 [<ffffffff81550a13>] filename_lookup fs/namei.c:2181 [inline]
 [<ffffffff81550a13>] user_path_at_empty+0x53/0x70 fs/namei.c:2362
 [<ffffffff81519bfe>] user_path_at include/linux/namei.h:52 [inline]
 [<ffffffff81519bfe>] SYSC_faccessat fs/open.c:378 [inline]
 [<ffffffff81519bfe>] SyS_faccessat fs/open.c:346 [inline]
 [<ffffffff81519bfe>] SYSC_access fs/open.c:426 [inline]
 [<ffffffff81519bfe>] SyS_access+0x20e/0x680 fs/open.c:424
 [<ffffffff838c2725>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: c1 e9 03 41 80 3c 39 00 0f 85 02 07 00 00 4d 85 f6 4c 89 30 74 24 49 8d 7e 08 49 b9 00 00 00 00 00 fc ff df 49 89 fa 49 c1 ea 03 <43> 80 3c 0a 00 0f 85 3f 06 00 00 49 89 46 08 48 b8 00 00 00 00 
RIP  [<ffffffff81e6f9ff>] __hlist_del include/linux/list.h:621 [inline]
RIP  [<ffffffff81e6f9ff>] hlist_del include/linux/list.h:626 [inline]
RIP  [<ffffffff81e6f9ff>] alloc_object lib/debugobjects.c:146 [inline]
RIP  [<ffffffff81e6f9ff>] __debug_object_init+0x2df/0xa90 lib/debugobjects.c:320
 RSP <ffff8801d99b7950>
---[ end trace 9e91629d3e5aece7 ]---