l2tp_core: tunl 4: sockfd_lookup(fd=9) returned -9
l2tp_core: tunl 4: sockfd_lookup(fd=9) returned -9
l2tp_core: tunl 4: sockfd_lookup(fd=9) returned -9
l2tp_core: tunl 4: sockfd_lookup(fd=10) returned -9
==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8801d20a7900 by task syz-executor6/4840

CPU: 0 PID: 4840 Comm: syz-executor6 Not tainted 4.4.131-g033c952 #36
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 d0e88947381104b7 ffff8800b2217c78 ffffffff81e0df8d
 ffffea0007482980 ffff8801d20a7900 0000000000000000 ffff8801d20a7900
 ffffffff82f18cb0 ffff8800b2217cb0 ffffffff8151520c ffff8801d20a7900
Call Trace:
 [<ffffffff81e0df8d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0df8d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151520c>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151552b>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151552b>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814f9004>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff83598784>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff835a52bf>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82f18b86>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18cc6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815225f5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522b35>] ____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
 [<ffffffff81007090>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81007090>] syscall_return_slowpath arch/x86/entry/common.c:348 [inline]
 [<ffffffff81007090>] do_syscall_32_irqs_on arch/x86/entry/common.c:398 [inline]
 [<ffffffff81007090>] do_fast_syscall_32+0x620/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c16aa>] sysenter_flags_fixed+0xd/0x17

Allocated by task 4840:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f80d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f83b7>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f83b7>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f4ad4>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff8359dbc9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8359dbc9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8359dbc9>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835a28d0>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1d5a8>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f1fee4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c16aa>] sysenter_flags_fixed+0xd/0x17

Freed by task 4847:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f80d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8a02>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8a02>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f5f04>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f5f04>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f5f04>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f5f04>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff8359ab30>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff8359cee9>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8359cee9>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff8359d9fb>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8348fff1>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f2e45d>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8348eca5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff832f695f>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff834194f0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f18b86>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18cc6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815225f5>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522b35>] ____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
 [<ffffffff81007090>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81007090>] syscall_return_slowpath arch/x86/entry/common.c:348 [inline]
 [<ffffffff81007090>] do_syscall_32_irqs_on arch/x86/entry/common.c:398 [inline]
 [<ffffffff81007090>] do_fast_syscall_32+0x620/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c16aa>] sysenter_flags_fixed+0xd/0x17

The buggy address belongs to the object at ffff8801d20a7900
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801d20a7900, ffff8801d20a7b00)
The buggy address belongs to the page:
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access[   53.260305] ------------[ cut here ]------------
WARNING: CPU: 1 PID: 3875 at kernel/sched/core.c:7950 __might_sleep+0x138/0x1a0 kernel/sched/core.c:7945()
do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff8113a6ee>] do_wait+0x26e/0xa30 kernel/exit.c:1507