random: nonblocking pool is initialized
==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8800b525aa00 by task syz-executor527/4032

CPU: 1 PID: 4032 Comm: syz-executor527 Not tainted 4.4.141-g8ddb600 #76
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 c286931854bfd17c ffff8801c6d37cc0 ffffffff81e1002d
 ffffea0002d49680 ffff8800b525aa00 0000000000000000 ffff8800b525aa00
 ffffffff82f1c220 ffff8801c6d37cf8 ffffffff81515ae6 ffff8800b525aa00
Call Trace:
 [<ffffffff81e1002d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e1002d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81515ae6>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff81515e05>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff81515e05>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814f98d4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8359d1c4>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff835a9cff>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82f1c0f6>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f1c236>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522ed5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81523415>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bdbf>] 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
 [<ffffffff838c4d35>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 4033:
 [<ffffffff81033c86>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f89a3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8c87>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8c87>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f53a4>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff835a2609>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff835a2609>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff835a2609>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835a7310>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f20b18>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f23454>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c4ba5>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 4033:
 [<ffffffff81033c86>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f89a3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f92d2>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f92d2>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f67d4>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f67d4>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f67d4>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f67d4>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff8359f570>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff835a1929>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff835a1929>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff835a243b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff83494761>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f319cd>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff83493415>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff832faecf>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff8341db40>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f1c0f6>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f1c236>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522ed5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81523415>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bdbf>] 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
 [<ffffffff838c4d35>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800b525aa00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b525aa00, ffff8800b525ac00)
The buggy address belongs to the page:
PANIC: double fault, error_code: 0x0
CPU: 1 PID: 4032 Comm: syz-executor527 Not tainted 4.4.141-g8ddb600 #76
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d8fe1800 task.stack: ffff8801c6d30000
RIP: 0010:[<ffffffff8148d002>]  [<ffffffff8148d002>] dump_page_badflags+0x12/0x70 mm/debug.c:84
RSP: 0018:ffff880100000000  EFLAGS: 00010046
RAX: ffff8801d8fe1800 RBX: ffffea0002d49680 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff83aaa220 RDI: ffffea0002d49680
RBP: ffff880100000020 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: ffffffff858ed134 R12: 0000000000000000
R13: ffffffff83aaa220 R14: ffff8800b525aa00 R15: ffff8800b525ac00
FS:  0000000002352880(0063) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8800fffffff8 CR3: 00000001c8672000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:

Call Trace:
 <UNK> 
Code: 47 9f 84 5b 5d c3 48 89 df e8 fb c8 06 00 eb dd 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41 56 41 55 49 89 f5 41 54 49 89 d4 <53> 48 89 fb 48 83 ec 08 e8 11 45 ec ff 48 89 da 48 b8 00 00 00