==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8801ca862500 by task syz-executor6/15881

CPU: 1 PID: 15881 Comm: syz-executor6 Not tainted 4.4.114-ga81d322 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 5cc97de419c6a31e ffff8800b4c1fc20 ffffffff81d0394d
 ffffea00072a1880 ffff8801ca862500 0000000000000000 ffff8801ca862500
 ffffffff82de7680 ffff8800b4c1fc58 ffffffff814fe1d3 ffff8801ca862500
Call Trace:
 [<ffffffff81d0394d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d0394d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fe1d3>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fe6e5>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fe6e5>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fe824>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8346450e>] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82dfc58a>] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447
 [<ffffffff82dfca57>] __sk_free+0x57/0x230 net/core/sock.c:1480
 [<ffffffff82dfcc60>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff834653ca>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff834653ca>] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82de752d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de7696>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815234e3>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81523a05>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff8100361d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100361d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:251
 [<ffffffff81007067>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81007067>] syscall_return_slowpath arch/x86/entry/common.c:347 [inline]
 [<ffffffff81007067>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
 [<ffffffff81007067>] do_fast_syscall_32+0x607/0x890 arch/x86/entry/common.c:457
 [<ffffffff8377586a>] sysenter_flags_fixed+0xd/0x17

Allocated by task 15871:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd243>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fd50d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fd50d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f97f4>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff8345e1c9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8345e1c9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8345e1c9>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff8346285c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82debee6>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82dee754>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d74>] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline]
 [<ffffffff81006d74>] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457
 [<ffffffff8377586a>] sysenter_flags_fixed+0xd/0x17

Freed by task 15871:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd243>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdb62>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdb62>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fa5fc>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fa5fc>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fa5fc>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fa5fc>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff8345a750>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345d001>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345d001>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345db6b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336c031>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82dfe62b>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff8336afe5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831cec9a>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f48a0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82de752d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de7696>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815234e3>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81523a05>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff8100361d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100361d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:251
 [<ffffffff81007067>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81007067>] syscall_return_slowpath arch/x86/entry/common.c:347 [inline]
 [<ffffffff81007067>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
 [<ffffffff81007067>] do_fast_syscall_32+0x607/0x890 arch/x86/entry/common.c:457
 [<ffffffff8377586a>] sysenter_flags_fixed+0xd/0x17

The buggy address belongs to the object at ffff8801ca862500
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801ca862500, ffff8801ca862700)
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: 0 Comm: swapper/0 Not tainted 4.4.114-ga81d322 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff84217840 task.stack: ffffffff84200000
RIP: 0010:[<ffffffff81d658b6>]  [<ffffffff81d658b6>] lookup_object lib/debugobjects.c:120 [inline]
RIP: 0010:[<ffffffff81d658b6>]  [<ffffffff81d658b6>] debug_object_deactivate+0x1a6/0x3c0 lib/debugobjects.c:465
RSP: 0018:ffff8801db207d20  EFLAGS: 00010003
RAX: 0000000000000092 RBX: 4f5f4755425f4d56 RCX: ffff8801cb157d28
RDX: 09ebe8eaa84be9ad RSI: ffffffff842c6460 RDI: 4f5f4755425f4d6e
RBP: ffff8801db207de8 R08: 1ffff1001676a218 R09: ffffffff8512d7d0
R10: 0000000000000001 R11: 1ffff1003b640f6a R12: 1ffff1003b640fa8
R13: 0000000000000003 R14: dffffc0000000000 R15: ffffffff8576ab48
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020b39f2f CR3: 00000001c7e00000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 000000000000003d ffffffff842c6460 ffff8801cb157d28 0000000000000092
 0000000041b58ab3 ffffffff83fce131 ffffffff81d65710 ffffffff84217840
 fffffbfff0843021 ffff8801db219658 ffffffff84218110 0000000000000000
Call Trace:
 <IRQ> 
 [<ffffffff812ada62>] debug_hrtimer_deactivate kernel/time/hrtimer.c:415 [inline]
 [<ffffffff812ada62>] debug_deactivate kernel/time/hrtimer.c:461 [inline]
 [<ffffffff812ada62>] __run_hrtimer kernel/time/hrtimer.c:1224 [inline]
 [<ffffffff812ada62>] __hrtimer_run_queues+0x492/0xfe0 kernel/time/hrtimer.c:1319
 [<ffffffff812afdb6>] hrtimer_interrupt+0x1a6/0x440 kernel/time/hrtimer.c:1353
 [<ffffffff810b0cda>] local_apic_timer_interrupt+0x6a/0xb0 arch/x86/kernel/apic/apic.c:901
 [<ffffffff83776b36>] smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:925
 [<ffffffff83775a90>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:737
 <EOI> 
 [<ffffffff81027ed5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81027ed5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:291
 [<ffffffff8102945a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:282
 [<ffffffff81221458>] default_idle_call+0x48/0x70 kernel/sched/idle.c:93
 [<ffffffff81221b5d>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff81221b5d>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff81221b5d>] cpu_startup_entry+0x5fd/0x8f0 kernel/sched/idle.c:301
 [<ffffffff83760e49>] rest_init+0x189/0x190 init/main.c:410
 [<ffffffff84821811>] start_kernel+0x6b9/0x6ee init/main.c:682
 [<ffffffff84820312>] x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196
 [<ffffffff84820454>] x86_64_start_kernel+0x140/0x163 arch/x86/kernel/head64.c:185
Code: eb 1a 48 89 da 48 c1 ea 03 42 80 3c 32 00 0f 85 86 01 00 00 48 8b 1b 48 85 db 74 7a 48 8d 7b 18 41 83 c5 01 48 89 fa 48 c1 ea 03 <42> 80 3c 32 00 0f 85 3c 01 00 00 48 3b 4b 18 75 c6 48 8d 7b 10 
RIP  [<ffffffff81d658b6>] lookup_object lib/debugobjects.c:120 [inline]
RIP  [<ffffffff81d658b6>] debug_object_deactivate+0x1a6/0x3c0 lib/debugobjects.c:465
 RSP <ffff8801db207d20>
---[ end trace b76e226f225d6964 ]---