==================================================================
BUG: KASAN: use-after-free in l2tp_session_create+0xf94/0x10f0 net/l2tp/l2tp_core.c:1824
Read of size 4 at addr ffff8801d1e16a10 by task syz-executor4/5614

CPU: 1 PID: 5614 Comm: syz-executor4 Not tainted 4.4.115-g0e9bcc1 #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 c0d5ac16b4c6b4a1 ffff8801c635fa30 ffffffff81d03dad
 ffffea0007478580 ffff8801d1e16a10 0000000000000000 ffff8801d1e16a10
 ffff8801d1e16a00 ffff8801c635fa68 ffffffff814fe1e3 ffff8801d1e16a10
Call Trace:
 [<ffffffff81d03dad>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d03dad>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fe1e3>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fe6f5>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fe6f5>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fe834>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8345f734>] l2tp_session_create+0xf94/0x10f0 net/l2tp/l2tp_core.c:1824
 [<ffffffff83462e6c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82dec476>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82deece4>] 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
 [<ffffffff83775eaa>] sysenter_flags_fixed+0xd/0x17

Allocated by task 5614:
 [<ffffffff81035de6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd253>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fd51d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fd51d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f9804>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff8345e7d9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8345e7d9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8345e7d9>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff83462e6c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82dec476>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82deece4>] 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
 [<ffffffff83775eaa>] sysenter_flags_fixed+0xd/0x17

Freed by task 5627:
 [<ffffffff81035de6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd253>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdb72>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdb72>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fa60c>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fa60c>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fa60c>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fa60c>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff8345ad60>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345d611>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345d611>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345e17b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336c641>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82dfebbb>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff8336b5f5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831cf2aa>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f4eb0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82de7abd>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de7c26>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815236a3>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81523bc5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9e4>] 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
 [<ffffffff83775eaa>] sysenter_flags_fixed+0xd/0x17

The buggy address belongs to the object at ffff8801d1e16a00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 16 bytes inside of
 512-byte region [ffff8801d1e16a00, ffff8801d1e16c00)
The buggy address belongs to the page:
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 3701 Comm: syz-executor4 Not tainted 4.4.115-g0e9bcc1 #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c6df9800 task.stack: ffff8801c6418000
RIP: 0010:[<ffffffff811a6ced>]  [<ffffffff811a6ced>] task_curr kernel/sched/core.c:1023 [inline]
RIP: 0010:[<ffffffff811a6ced>]  [<ffffffff811a6ced>] kick_process+0xdd/0x1c0 kernel/sched/core.c:1565
RSP: 0018:ffff8801c641fb10  EFLAGS: 00010006
RAX: dffffc0000000000 RBX: 000000000001f4c0 RCX: ffffffff81d63b5b
RDX: 00000000b6c55718 RSI: ffffffff839fe320 RDI: 00000005b62ab8c0
RBP: ffff8801c641fb30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 1ffff10038c83f1a R12: ffff8801cf5ab000
R13: 00000000c6358050 R14: 00000000c6358050 R15: ffff8800b15633c0
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000088c1900
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000008114628 CR3: 00000001c6416000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801cf5ab000 0000000000000080 0000000000000080 ffff8801d0a965c0
 ffff8801c641fb50 ffffffff81153c35 ffff8801cf5ab000 ffff8801cf786000
 ffff8801c641fba8 ffffffff81153f6d 0000000000000009 ffff8800b1563428
Call Trace:
 [<ffffffff81153c35>] signal_wake_up_state+0x55/0x70 kernel/signal.c:660
 [<ffffffff81153f6d>] signal_wake_up include/linux/sched.h:3319 [inline]
 [<ffffffff81153f6d>] complete_signal+0x2ed/0x700 kernel/signal.c:952
 [<ffffffff81155b7f>] __send_signal+0x90f/0x1330 kernel/signal.c:1080
 [<ffffffff811565ea>] send_signal+0x4a/0xc0 kernel/signal.c:1096
 [<ffffffff81158d74>] do_send_sig_info+0xa4/0x130 kernel/signal.c:1151
 [<ffffffff81159bfd>] group_send_sig_info+0xdd/0x170 kernel/signal.c:1273
 [<ffffffff81159d20>] __kill_pgrp_info+0x90/0x120 kernel/signal.c:1291
 [<ffffffff8115a326>] kill_something_info kernel/signal.c:1397 [inline]
 [<ffffffff8115a326>] SYSC_kill+0x366/0x5b0 kernel/signal.c:2867
 [<ffffffff811604fc>] SyS_kill+0x1c/0x30 kernel/signal.c:2857
 [<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
 [<ffffffff83775eaa>] sysenter_flags_fixed+0xd/0x17
Code: 04 02 84 c0 74 08 3c 03 0f 8e b7 00 00 00 48 b8 00 00 00 00 00 fc ff df 45 8b 6d 10 4a 8d 3c ed 40 b6 7e 84 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 be 00 00 00 4a 03 1c ed 40 b6 7e 84 48 b8 00 
RIP  [<ffffffff811a6ced>] task_curr kernel/sched/core.c:1023 [inline]
RIP  [<ffffffff811a6ced>] kick_process+0xdd/0x1c0 kernel/sched/core.c:1565
 RSP <ffff8801c641fb10>
---[ end trace a7e7e775b3aba89f ]---