==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8800ba5fc000 by task syz-executor3/7493

CPU: 0 PID: 7493 Comm: syz-executor3 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 c06130ddcf7a6c23 ffff8801d293fa78 ffffffff81e15fed
 ffffea0002e97f00 ffff8800ba5fc000 0000000000000000 ffff8800ba5fc000
 0000000000000000 ffff8801d293fab0 ffffffff8151b489 ffff8800ba5fc000
Call Trace:
 [<ffffffff81e15fed>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e15fed>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151b489>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151b7a8>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151b7a8>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814fe714>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff835a4b64>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff835b166f>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82f210c9>] __sock_release+0xd9/0x260 net/socket.c:592
 [<ffffffff82f21269>] sock_close+0x19/0x20 net/socket.c:1050
 [<ffffffff81528875>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81528db5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118ee4f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff81162290>] get_signal+0x1190/0x14b0 kernel/signal.c:2151
 [<ffffffff8100df4b>] do_signal+0x8b/0x1d30 arch/x86/kernel/signal.c:712
 [<ffffffff8100360a>] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:249
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349
 [<ffffffff838cc6f5>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 7475:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd7d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdab7>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdab7>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814fa1f4>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff835a9f79>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff835a9f79>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff835a9f79>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835aec80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27bf8>] SYSC_connect+0x1b8/0x300 net/socket.c:1570
 [<ffffffff82f2a544>] SyS_connect+0x24/0x30 net/socket.c:1551
 [<ffffffff838cc565>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 7475:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd7d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fe102>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fe102>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fb664>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fb664>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fb664>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fb664>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff835a6ee0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff835a9299>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff835a9299>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff835a9dab>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8349bc11>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f38add>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8349a8c5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff8330244f>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff83424ec0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f210c9>] __sock_release+0xd9/0x260 net/socket.c:592
 [<ffffffff82f21269>] sock_close+0x19/0x20 net/socket.c:1050
 [<ffffffff81528875>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81528db5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118ee4f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff8100362d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100362d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:253
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349
 [<ffffffff838cc6f5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800ba5fc000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800ba5fc000, ffff8800ba5fc200)
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: 1 PID: 3745 Comm: syz-executor7 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bbaab000 task.stack: ffff8800a51a8000
RIP: 0010:[<ffffffff81e7801c>]  [<ffffffff81e7801c>] lookup_object lib/debugobjects.c:120 [inline]
RIP: 0010:[<ffffffff81e7801c>]  [<ffffffff81e7801c>] debug_object_free+0xec/0x400 lib/debugobjects.c:559
RSP: 0018:ffff8800a51afd70  EFLAGS: 00010002
RAX: 0000000000000296 RBX: 4000000000004080 RCX: 0000000000000000
RDX: 0800000000000813 RSI: 1ffff1003a4dc0ee RDI: 4000000000004098
RBP: ffff8800a51afda8 R08: ffffffff8535ea00 R09: 0000000000000001
R10: 0000000000000001 R11: ffff8800bbaab000 R12: ffffffff85998428
R13: ffff8800a51afdf8 R14: 0000000000000003 R15: dffffc0000000000
FS:  0000000000ca9940(0063) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f26b36f8000 CR3: 00000000b28d1000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801db3196c0 ffffffff844c77a0 0000000000000000 0000000000100590
 ffff8800a51afdf8 ffff8800a51afe98 0000000000000001 ffff8800a51afec0
 ffffffff812a3683 0000000000000000 000000000000c350 1ffff10014a35fbb
Call Trace:
 [<ffffffff812a3683>] destroy_hrtimer_on_stack kernel/time/hrtimer.c:436 [inline]
 [<ffffffff812a3683>] hrtimer_nanosleep+0x373/0x540 kernel/time/hrtimer.c:1595
 [<ffffffff812a390e>] SYSC_nanosleep kernel/time/hrtimer.c:1610 [inline]
 [<ffffffff812a390e>] SyS_nanosleep+0xbe/0x110 kernel/time/hrtimer.c:1599
 [<ffffffff838cc565>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: 78 02 00 00 48 8b 1b 41 be 01 00 00 00 48 85 db 74 44 49 bf 00 00 00 00 00 fc ff df 48 8d 7b 18 41 83 c6 01 48 89 fa 48 c1 ea 03 <42> 80 3c 3a 00 0f 85 0a 02 00 00 4c 3b 6b 18 74 49 48 89 da 48 
RIP  [<ffffffff81e7801c>] lookup_object lib/debugobjects.c:120 [inline]
RIP  [<ffffffff81e7801c>] debug_object_free+0xec/0x400 lib/debugobjects.c:559
 RSP <ffff8800a51afd70>
---[ end trace 00108de3d98be559 ]---