==================================================================
BUG: KASAN: use-after-free in l2tp_session_create+0xde0/0x1030 net/l2tp/l2tp_core.c:1828
Read of size 4 at addr ffff8800af568f10 by task syz-executor0/24711

CPU: 1 PID: 24711 Comm: syz-executor0 Not tainted 4.4.153-g5e24b4e #90
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 e55e2123195eeb24 ffff8801d40afaa8 ffffffff81e162ed
 ffffea0002bd5a00 ffff8800af568f10 0000000000000000 ffff8800af568f10
 ffff8801d46a3348 ffff8801d40afae0 ffffffff8151b4d9 ffff8800af568f10
Call Trace:
 [<ffffffff81e162ed>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e162ed>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151b4d9>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151b7f8>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151b7f8>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814fe764>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff835ab020>] l2tp_session_create+0xde0/0x1030 net/l2tp/l2tp_core.c:1828
 [<ffffffff835aef80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27ef8>] SYSC_connect+0x1b8/0x300 net/socket.c:1570
 [<ffffffff82f2a844>] SyS_connect+0x24/0x30 net/socket.c:1551
 [<ffffffff838cc865>] entry_SYSCALL_64_fastpath+0x22/0x9e

Allocated by task 24711:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd823>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdb07>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdb07>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814fa244>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff835aa279>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff835aa279>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff835aa279>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835aef80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27ef8>] SYSC_connect+0x1b8/0x300 net/socket.c:1570
 [<ffffffff82f2a844>] SyS_connect+0x24/0x30 net/socket.c:1551
 [<ffffffff838cc865>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 24704:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd823>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fe152>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fe152>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fb6b4>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fb6b4>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fb6b4>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fb6b4>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff835a71e0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff835a9599>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff835a9599>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff835aa0ab>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8349bf11>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f38ddd>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8349abc5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff8330274f>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff834251c0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f213c9>] __sock_release+0xd9/0x260 net/socket.c:592
 [<ffffffff82f21569>] sock_close+0x19/0x20 net/socket.c:1050
 [<ffffffff815288c5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81528e05>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118ee9f>] 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
 [<ffffffff838cc9f5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800af568f00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 16 bytes inside of
 512-byte region [ffff8800af568f00, ffff8800af569100)
The buggy address belongs to the page:
page:ffffea0002bd5a00 count:1 mapcount:-2146697203 mapping:          (null) index:0x0
flags: 0xffff8801d280fc59([  287.563753] syz-executor1: Corrupted page table at address 482b61
PGD 1cd288067 PUD 1d2c5d067 PMD ffffffff814902b7 
Bad pagetable: 001d [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 24723 Comm: syz-executor1 Not tainted 4.4.153-g5e24b4e #90
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800aef88000 task.stack: ffff8801ca3a0000
RIP: 0033:[<0000000000482b61>]  [<0000000000482b61>] 0x482b61
RSP: 002b:0000000000a3fbf0  EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000046003 RCX: 0000000000482b61
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000a3fc00
RBP: 00000000009300a0 R08: ffffffffffffffff R09: ffffffffffffffff
R10: 0000000000a3fcf0 R11: 0000000000000293 R12: 0000000000930aa0
R13: 000000000093014c R14: 0000000000045d4a R15: 0000000000045d1d
FS:  0000000001742940(0063) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000482b61 CR3: 00000001ca81b000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

RIP  [<0000000000482b61>] 0x482b61
 RSP <0000000000a3fbf0>
---[ end trace c6ccf761e193dd0e ]---