==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xf2/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8801cbda1680 by task syz-executor0/12165

CPU: 1 PID: 12165 Comm: syz-executor0 Not tainted 4.4.132-g1d92c59 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 38fd70992644a1e0 ffff8801d1fc7c68 ffffffff81e0dfad
 ffffea00072f6800 ffff8801cbda1680 0000000000000000 ffff8801cbda1680
 ffffffff82f18e50 ffff8801d1fc7ca0 ffffffff8151527c ffff8801cbda1680
Call Trace:
 [<ffffffff81e0dfad>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0dfad>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151527c>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151559b>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151559b>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814f9074>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff835a46c2>] pppol2tp_session_destruct+0xf2/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82f2debc>] sk_destruct+0x4c/0x4c0 net/core/sock.c:1447
 [<ffffffff82f2e48e>] __sk_free+0x15e/0x220 net/core/sock.c:1480
 [<ffffffff82f2e580>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff835a547a>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff835a547a>] pppol2tp_release+0x26a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82f18d26>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18e66>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522665>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522ba5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bb8f>] 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: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
 [<ffffffff838c03f5>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 12165:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f8143>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8427>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8427>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f4b44>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff8359dd19>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8359dd19>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8359dd19>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835a2a20>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1d748>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f20084>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c0265>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 12155:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f8143>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8a72>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8a72>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f5f74>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f5f74>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f5f74>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f5f74>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff8359ac80>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff8359d039>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8359d039>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff8359db4b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff83490141>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f2e5fd>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8348edf5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff832f6acf>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff83419660>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f18d26>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18e66>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522665>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522ba5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bb8f>] 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: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
 [<ffffffff838c03f5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8801cbda1680
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801cbda1680, ffff8801cbda1880)
The buggy address belongs to the page:
BUG: unable to handle kernel paging request at fffffffb8ee79678
IP: [<ffffffff81224a95>] cpuacct_charge+0x155/0x380 kernel/sched/cpuacct.c:247
PGD 440f067 PUD 0 
Oops: 0000 [#1] PREEMPT SMP K
BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: [<          (null)>]           (null)
PGD b42d6067 PUD b42d7067 PMD 0 
Thread overran stack, or stack corrupted
Oops: 0010 [#2] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 12166 Comm: syz-executor2 Not tainted 4.4.132-g1d92c59 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d3c30000 task.stack: ffff8801cc838000
RIP: 0010:[<0000000000000000>]  [<          (null)>]           (null)
RSP: 0018:ffff8801cc83ea18  EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8801cbda1880 RCX: ffffc90002ce5000
RDX: 0000000000040000 RSI: 0000000000000005 RDI: ffff8801cbda1880
RBP: ffffffff8148c9b7 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: ffffffff858ed104 R12: 00000000cc83ea47
R13: 0000000000000020 R14: fffffbfff0c554df R15: fffffbfff0c554a1
FS:  00007fba45b93700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000b2ab9000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff82084c5f ffffea00072f6800 0000000000000000 ffffffff83aa9be0
 ffff8801cbda1680 ffff8801cbda1880 ffff8801cc83ea88 ffffffff8148c9b7
 0000000000000041 ffffea00072f6800 0000000000000000 ffffffff83aa9be0
Call Trace:
Code:  Bad RIP value.
RIP  [<          (null)>]           (null)
 RSP <ffff8801cc83ea18>
CR2: 0000000000000000
---[ end trace 7a10a5b914f316d6 ]---