==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8801d0cfc000 by task syz-executor906/3945

CPU: 1 PID: 3945 Comm: syz-executor906 Not tainted 4.4.138-g07c0138 #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 6723b49ed928e8e6 ffff8801d933fb50 ffffffff81e0ed0d
 ffffea0007433f00 ffff8801d0cfc000 0000000000000000 ffff8801d0cfc000
 ffffffff82f1a2b0 ffff8801d933fb88 ffffffff81515a16 ffff8801d0cfc000
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 3943:
 [<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 3915:
 [<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 ffff8801d0cfc000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801d0cfc000, ffff8801d0cfc200)
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: 3846 Comm: syz-executor906 Not tainted 4.4.138-g07c0138 #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bb2d4800 task.stack: ffff8800bae20000
RIP: 0010:[<ffffffff81e70801>]  [<ffffffff81e70801>] lookup_object lib/debugobjects.c:120 [inline]
RIP: 0010:[<ffffffff81e70801>]  [<ffffffff81e70801>] debug_object_deactivate+0x191/0x340 lib/debugobjects.c:465
RSP: 0018:ffff8801db207cf0  EFLAGS: 00010803
RAX: dffffc0000000000 RBX: b5a0012500000f67 RCX: 16b40024a00001ef
RDX: 0000000000000000 RSI: ffffffff844c6720 RDI: b5a0012500000f7f
RBP: ffff8801db207da8 R08: ffffffff8535b750 R09: 0000000000000001
R10: 0000000000000001 R11: ffff8800bb2d4800 R12: 1ffff1003b640fa0
R13: ffffffff85a3bc68 R14: ffff8801db219c40 R15: 0000000000000003
FS:  00000000008db940(0063) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000008db958 CR3: 00000000ac475000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000092 ffffffff844c6720 0000000041b58ab3 ffffffff842092d7
 ffffffff81e70670 ffff8800bb2d4800 ffffed001765aa1b ffff8800bb2d50e0
 ffff8801db219658 0000000000000001 ffff8801db207d80 ffffffff81229682
Call Trace:
 <IRQ> 
 [<ffffffff8129dbc2>] debug_hrtimer_deactivate kernel/time/hrtimer.c:415 [inline]
 [<ffffffff8129dbc2>] debug_deactivate kernel/time/hrtimer.c:462 [inline]
 [<ffffffff8129dbc2>] __run_hrtimer kernel/time/hrtimer.c:1230 [inline]
 [<ffffffff8129dbc2>] __hrtimer_run_queues+0x222/0x1000 kernel/time/hrtimer.c:1325
 [<ffffffff8129f4c1>] hrtimer_interrupt+0x1b1/0x430 kernel/time/hrtimer.c:1359
 [<ffffffff810ad284>] local_apic_timer_interrupt+0x74/0xa0 arch/x86/kernel/apic/apic.c:901
 [<ffffffff838c534c>] smp_apic_timer_interrupt+0x7c/0xa0 arch/x86/kernel/apic/apic.c:925
 [<ffffffff838c4290>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:741
 <EOI> 
 [<ffffffff812d4359>] smp_call_function_many+0x5b9/0x710 kernel/smp.c:435
 [<ffffffff810e8fad>] native_flush_tlb_others+0xfd/0x6e0 arch/x86/mm/tlb.c:292
 [<ffffffff810e969c>] flush_tlb_others arch/x86/include/asm/paravirt.h:338 [inline]
 [<ffffffff810e969c>] flush_tlb_mm_range+0x10c/0x540 arch/x86/mm/tlb.c:358
 [<ffffffff8112bdb9>] dup_mmap kernel/fork.c:528 [inline]
 [<ffffffff8112bdb9>] dup_mm kernel/fork.c:983 [inline]
 [<ffffffff8112bdb9>] copy_mm kernel/fork.c:1037 [inline]
 [<ffffffff8112bdb9>] copy_process+0x4709/0x63e0 kernel/fork.c:1503
 [<ffffffff8112dea6>] _do_fork+0x146/0xe10 kernel/fork.c:1784
 [<ffffffff8112ec47>] SYSC_clone kernel/fork.c:1893 [inline]
 [<ffffffff8112ec47>] SyS_clone+0x37/0x50 kernel/fork.c:1887
 [<ffffffff838c2725>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: a9 01 00 00 48 8b 1b 41 bf 01 00 00 00 48 85 db 74 42 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 18 41 83 c7 01 48 89 f9 48 c1 e9 03 <80> 3c 01 00 0f 85 0c 01 00 00 4c 3b 73 18 74 7d 48 89 d9 48 c1 
RIP  [<ffffffff81e70801>] lookup_object lib/debugobjects.c:120 [inline]
RIP  [<ffffffff81e70801>] debug_object_deactivate+0x191/0x340 lib/debugobjects.c:465
 RSP <ffff8801db207cf0>
---[ end trace 6ae77d55b75e44d3 ]---