==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800b5836c80 by task syz-executor3/6347

CPU: 1 PID: 6347 Comm: syz-executor3 Not tainted 4.4.125-g38f41ec #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 8f42d8b645cf082c ffff8800a1207c68 ffffffff81d067bd
 ffffea0002d60d80 ffff8800b5836c80 0000000000000000 ffff8800b5836c80
 ffffffff82ded950 ffff8800a1207ca0 ffffffff814fea83 ffff8800b5836c80
Call Trace:
 [<ffffffff81d067bd>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d067bd>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fea83>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fef95>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fef95>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814ff0d4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8346b0ce>] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82e0285a>] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447
 [<ffffffff82e02d27>] __sk_free+0x57/0x230 net/core/sock.c:1480
 [<ffffffff82e02f30>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff8346bf8a>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff8346bf8a>] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82ded7fd>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82ded966>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81523f43>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81524465>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bd44>] 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:252
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348
 [<ffffffff83779af5>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 6339:
 [<ffffffff81035d76>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fdaf3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fddbd>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fddbd>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814fa0a4>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff83464d89>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff83464d89>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff83464d89>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff8346941c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82df21b6>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82df4a24>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff83779965>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 6339:
 [<ffffffff81035d76>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fdaf3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fe412>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fe412>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814faeac>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814faeac>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814faeac>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814faeac>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff83461310>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff83463bc1>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff83463bc1>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8346472b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff833729c1>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82e048fb>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff83371975>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831d5eba>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832fb320>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82ded7fd>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82ded966>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81523f43>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81524465>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bd44>] 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:252
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348
 [<ffffffff83779af5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800b5836c80
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b5836c80, ffff8800b5836e80)
The buggy address belongs to the page:
BUG: unable to handle kernel paging request at fffffffb8ec761c8
IP: [<ffffffff8122ba55>] cpuacct_charge+0x155/0x390 kernel/sched/cpuacct.c:247
PGD 420f067 PUD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 3686 Comm: syz-fuzzer Not tainted 4.4.125-g38f41ec #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800b127e000 task.stack: ffff8801cc688000
RIP: 0010:[<ffffffff8122ba55>]  [<ffffffff8122ba55>] cpuacct_charge+0x155/0x390 kernel/sched/cpuacct.c:247
RSP: 0018:ffff8801cc68f8c0  EFLAGS: 00010046
RAX: 1ffffffff0855007 RBX: 0000000000018528 RCX: ffffffff847ec9c0
RDX: fffffbff71d8ec39 RSI: fffffffb8ec761c8 RDI: ffffffff842a8038
RBP: ffff8801cc68f908 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff100398d1ee4 R12: ffffffff842a7f60
R13: dffffc0000000000 R14: 00000000218c39c6 R15: ffffffff81491301
FS:  000000c4201a2068(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffb8ec761c8 CR3: 00000000b6e04000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8122b960 ffff8801cc68f8f0 0000000000000046 0000000000000003
 ffff8800b6811860 ffffffff83844600 00000000218c39c6 ffff8800b68118b0
 ffff8800b6811800 ffff8801cc68f958 ffffffff811dd0c7 ffff8801db31f4c0
Call Trace:
 [<ffffffff811dd0c7>] update_curr+0x2c7/0x6c0 kernel/sched/fair.c:882
 [<ffffffff811e5253>] enqueue_entity kernel/sched/fair.c:3511 [inline]
 [<ffffffff811e5253>] enqueue_task_fair+0x313/0x2940 kernel/sched/fair.c:4694
 [<ffffffff811bc208>] enqueue_task kernel/sched/core.c:858 [inline]
 [<ffffffff811bc208>] activate_task+0x148/0x270 kernel/sched/core.c:874
 [<ffffffff811bd1af>] ttwu_activate kernel/sched/core.c:1736 [inline]
 [<ffffffff811bd1af>] ttwu_do_activate.constprop.131+0xbf/0x1e0 kernel/sched/core.c:1789
 [<ffffffff811c059d>] ttwu_queue kernel/sched/core.c:1934 [inline]
 [<ffffffff811c059d>] try_to_wake_up+0x68d/0xf60 kernel/sched/core.c:2068
 [<ffffffff811c0f2e>] wake_up_q+0xbe/0x130 kernel/sched/core.c:582
 [<ffffffff812db8dd>] futex_wake+0x3ad/0x450 kernel/futex.c:1364
 [<ffffffff812e188e>] do_futex+0x78e/0x15d0 kernel/futex.c:3106
 [<ffffffff812e28d8>] SYSC_futex kernel/futex.c:3162 [inline]
 [<ffffffff812e28d8>] SyS_futex+0x208/0x2c0 kernel/futex.c:3130
 [<ffffffff83779965>] entry_SYSCALL_64_fastpath+0x22/0x9e
Code: 49 8d bc 24 d8 00 00 00 48 89 f8 48 c1 e8 03 42 80 3c 28 00 0f 85 9e 01 00 00 49 8b 9c 24 d8 00 00 00 80 3a 00 0f 85 0a 02 00 00 <4a> 03 1c f9 48 89 d8 48 c1 e8 03 42 80 3c 28 00 0f 85 cf 01 00 
RIP  [<ffffffff8122ba55>] cpuacct_charge+0x155/0x390 kernel/sched/cpuacct.c:247
 RSP <ffff8801cc68f8c0>
CR2: fffffffb8ec761c8
---[ end trace a371c3deb753f78c ]---