==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800aa6cca00 by task syz-executor0/7129

CPU: 1 PID: 7129 Comm: syz-executor0 Not tainted 4.4.114-ga81d322 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 2e4f357c939d570a ffff8800aa037c20 ffffffff81d0394d
 ffffea0002a9b300 ffff8800aa6cca00 0000000000000000 ffff8800aa6cca00
 ffffffff82de7680 ffff8800aa037c58 ffffffff814fe1d3 ffff8800aa6cca00
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 7129:
 [<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 7131:
 [<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 ffff8800aa6cca00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800aa6cca00, ffff8800aa6ccc00)
The buggy address belongs to the page:
kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
BUG: unable to handle kernel paging request at ffff8800aa017d80
IP: [<ffff8800aa017d80>] 0xffff8800aa017d80
PGD 60eb067 PUD 21ffff067 PMD 80000000aa0000e3 
Thread overran stack, or stack corrupted
Oops: 0011 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 4185 Comm: kworker/0:2 Not tainted 4.4.114-ga81d322 #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800b7638000 task.stack: ffff8800aa010000
RIP: 0010:[<ffff8800aa017d80>]  [<ffff8800aa017d80>] 0xffff8800aa017d80
RSP: 0018:ffff8800aa017d48  EFLAGS: 00010282
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 1ffff1003b643fc4 RSI: 0000000000000001 RDI: ffff8801db21fe20
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffea0002a9b300
R13: 0000000000000000 R14: ffffffff838a8e60 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000130 CR3: 00000000bb850000 CR4: 0000000000160674
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81490a51 dffffc0000000000 ffffea0002a9b300 0000000000000000
 ffffffff838a8e60 0000000000000000 0000000000000000 ffff8800aa017dc0
 ffffffff81490a51 ffff8801db31fdb8 ffffea0002a9b300 0000000000000000
Call Trace:
Code: fc ff df 00 b3 a9 02 00 ea ff ff 00 00 00 00 00 00 00 00 60 8e 8a 83 ff ff ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <c0> 7d 01 aa 00 88 ff ff 51 0a 49 81 ff ff ff ff b8 fd 31 db 01 
RIP  [<ffff8800aa017d80>] 0xffff8800aa017d80
 RSP <ffff8800aa017d48>
CR2: ffff8800aa017d80
---[ end trace 20083b2bdc9f530f ]---