==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8800b5e53680 by task syz-executor3/5935

CPU: 0 PID: 5935 Comm: syz-executor3 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
 0000000000000000 c221f2064604424f ffff8800a451fa78 ffffffff81e15fed
 ffffea0002d79480 ffff8800b5e53680 0000000000000000 ffff8800b5e53680
 0000000000000000 ffff8800a451fab0 ffffffff8151b489 ffff8800b5e53680
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 5912:
 [<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 5955:
 [<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 ffff8800b5e53680
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b5e53680, ffff8800b5e53880)
The buggy address belongs to the page:
BUG: unable to handle kernel paging request at fffffffd33cb2a80
IP: [<ffffffff81227d85>] cpuacct_charge+0x155/0x380 kernel/sched/cpuacct.c:247
PGD 440f067 PUD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 3653 Comm: syz-fuzzer Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800b36d0000 task.stack: ffff8801cfff0000
RIP: 0010:[<ffffffff81227d85>]  [<ffffffff81227d85>] cpuacct_charge+0x155/0x380 kernel/sched/cpuacct.c:247
RSP: 0018:ffff8801cfff7ca0  EFLAGS: 00010046
RAX: 1ffffffff089521f RBX: 00000000000185a8 RCX: ffffffff84a16680
RDX: fffffbffa6796550 RSI: fffffffd33cb2a80 RDI: ffffffff844a90f8
RBP: ffff8801cfff7ce0 R08: ffff8800b36d0978 R09: 0000000000000001
R10: 0000000000000001 R11: ffff8800b36d0000 R12: ffffffff844a9020
R13: dffffc0000000000 R14: 000000000e01a133 R15: ffffffffb5e53880
FS:  000000c420028e68(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffd33cb2a80 CR3: 00000000b3734000 CR4: 00000000001606f0
Stack:
 ffffffff81227c90 0000000000000046 0000000000000003 ffff8800a4b88060
 ffff8800a4b88000 000000000e01a133 ffff8800a4b880b0 0000000000000000
 ffff8801cfff7d28 ffffffff811dc309 0000000000000005 ffff8801db21f558
Call Trace:
 [<ffffffff811dc309>] update_curr+0x2c9/0x6d0 kernel/sched/fair.c:882
 [<ffffffff811e750a>] enqueue_entity kernel/sched/fair.c:3512 [inline]
 [<ffffffff811e750a>] enqueue_task_fair+0x2fa/0x2790 kernel/sched/fair.c:4695
 [<ffffffff811be9ed>] enqueue_task kernel/sched/core.c:858 [inline]
 [<ffffffff811be9ed>] activate_task+0x14d/0x280 kernel/sched/core.c:874
 [<ffffffff811bfa1f>] ttwu_activate kernel/sched/core.c:1736 [inline]
 [<ffffffff811bfa1f>] ttwu_do_activate.constprop.109+0xbf/0x1e0 kernel/sched/core.c:1789
 [<ffffffff811c2c30>] ttwu_queue kernel/sched/core.c:1934 [inline]
 [<ffffffff811c2c30>] try_to_wake_up+0x660/0xf00 kernel/sched/core.c:2068
 [<ffffffff811c5780>] wake_up_state+0x10/0x20 kernel/sched/core.c:2148
 [<ffffffff81158b04>] signal_wake_up_state+0x44/0x70 kernel/signal.c:659
 [<ffffffff8115d593>] signal_wake_up include/linux/sched.h:3332 [inline]
 [<ffffffff8115d593>] zap_other_threads+0x123/0x170 kernel/signal.c:1213
 [<ffffffff8113e34c>] do_group_exit+0x26c/0x330 kernel/exit.c:880
 [<ffffffff8113e42d>] SYSC_exit_group kernel/exit.c:896 [inline]
 [<ffffffff8113e42d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:894
 [<ffffffff838cc565>] 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 c4 01 00 00 49 8b 9c 24 d8 00 00 00 80 3a 00 0f 85 8f 01 00 00 <4a> 03 1c f9 48 89 d8 48 c1 e8 03 42 80 3c 28 00 0f 85 be 01 00 
RIP  [<ffffffff81227d85>] cpuacct_charge+0x155/0x380 kernel/sched/cpuacct.c:247
 RSP <ffff8801cfff7ca0>
CR2: fffffffd33cb2a80
---[ end trace 6926d836b48180ba ]---