==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8801d0976c80 by task syzkaller155728/3361

CPU: 1 PID: 3361 Comm: syzkaller155728 Not tainted 4.4.113-gef588ef #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 720c82d90901b1da ffff8801d0af78c8 ffffffff81d0278d
 ffffea0007425d80 ffff8801d0976c80 0000000000000000 ffff8801d0976c80
 ffffffff82de6370 ffff8801d0af7900 ffffffff814fd053 ffff8801d0976c80
Call Trace:
 [<ffffffff81d0278d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d0278d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fd053>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fd565>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fd565>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fd6a4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff83455f48>] l2tp_session_queue_purge+0xe8/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff83462fdf>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82de621d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de6386>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522363>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81522885>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff81132f7a>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff81132f7a>] do_exit+0x82a/0x2a10 kernel/exit.c:755
 [<ffffffff81139418>] do_group_exit+0x108/0x320 kernel/exit.c:885
 [<ffffffff8115c872>] get_signal+0x4f2/0x1550 kernel/signal.c:2317
 [<ffffffff8100e7fb>] do_signal+0x8b/0x1d40 arch/x86/kernel/signal.c:712
 [<ffffffff810035fa>] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:247
 [<ffffffff81006363>] prepare_exit_to_usermode+0xe3/0x100 arch/x86/entry/common.c:282
 [<ffffffff83772708>] retint_user+0x8/0x3c

Allocated by task 3360:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc0c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fc38d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fc38d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f8674>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff8345be59>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8345be59>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8345be59>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff834604ec>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82deabd6>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82ded444>] 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
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17

Freed by task 3323:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc0c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fc9e2>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fc9e2>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f947c>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f947c>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f947c>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f947c>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff834583e0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345ac91>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345ac91>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345b7fb>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336a031>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82dfd31b>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff83368fe5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831cd12a>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f2920>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82de621d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de6386>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522363>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81522885>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff81132f7a>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff81132f7a>] do_exit+0x82a/0x2a10 kernel/exit.c:755
 [<ffffffff81139418>] do_group_exit+0x108/0x320 kernel/exit.c:885
 [<ffffffff8115c872>] get_signal+0x4f2/0x1550 kernel/signal.c:2317
 [<ffffffff8100e7fb>] do_signal+0x8b/0x1d40 arch/x86/kernel/signal.c:712
 [<ffffffff810035fa>] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:247
 [<ffffffff81006363>] prepare_exit_to_usermode+0xe3/0x100 arch/x86/entry/common.c:282
 [<ffffffff83772708>] retint_user+0x8/0x3c

The buggy address belongs to the object at ffff8801d0976c80
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801d0976c80, ffff8801d0976e80)
The buggy address belongs to the page:
BUG: unable to handle kernel paging request at fffffffba0d32400
IP: [<ffffffff8122a525>] 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: 3321 Comm: syzkaller155728 Not tainted 4.4.113-gef588ef #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d22217c0 task.stack: ffff8800b5a20000
RIP: 0010:[<ffffffff8122a525>]  [<ffffffff8122a525>] cpuacct_charge+0x155/0x390 kernel/sched/cpuacct.c:247
RSP: 0018:ffff8800b5a27ba0  EFLAGS: 00010046
RAX: 1ffffffff0854fff RBX: 0000000000018528 RCX: ffffffff847eb500
RDX: fffffbff741a6480 RSI: fffffffba0d32400 RDI: ffffffff842a7ff8
RBP: ffff8800b5a27be8 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff10016b44f40 R12: ffffffff842a7f20
R13: dffffc0000000000 R14: 000000000021b5f8 R15: ffffffff838a8de0
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000083bc840
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: fffffffba0d32400 CR3: 00000000b4bbc000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8122a430 ffff8800b5a27bd0 0000000000000046 0000000000000003
 ffff8801d0b00060 ffffffff83844340 000000000021b5f8 ffff8801d0b000b0
 ffff8801d0b00000 ffff8800b5a27c38 ffffffff811dbea7 ffff8801db31f4c0
Call Trace:
 [<ffffffff811dbea7>] update_curr+0x2c7/0x6c0 kernel/sched/fair.c:882
 [<ffffffff811e4033>] enqueue_entity kernel/sched/fair.c:3511 [inline]
 [<ffffffff811e4033>] enqueue_task_fair+0x313/0x2940 kernel/sched/fair.c:4694
 [<ffffffff811bb7f8>] enqueue_task kernel/sched/core.c:856 [inline]
 [<ffffffff811bb7f8>] activate_task+0x148/0x270 kernel/sched/core.c:872
 [<ffffffff811c6c34>] wake_up_new_task+0x644/0xe20 kernel/sched/core.c:2487
 [<ffffffff8112b974>] _do_fork+0x244/0xe00 kernel/fork.c:1808
 [<ffffffff8112c607>] SYSC_clone kernel/fork.c:1893 [inline]
 [<ffffffff8112c607>] SyS_clone+0x37/0x50 kernel/fork.c:1887
 [<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
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17
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  [<ffffffff8122a525>] cpuacct_charge+0x155/0x390 kernel/sched/cpuacct.c:247
 RSP <ffff8800b5a27ba0>
CR2: fffffffba0d32400
---[ end trace 2269215e0c8a313e ]---