==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800b4fd4000 by task syzkaller515799/3760

CPU: 1 PID: 3760 Comm: syzkaller515799 Not tainted 4.4.112-g3fc4284 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 f2d1fe4ac8580672 ffff8801d02e7c70 ffffffff81d054ed
 ffffea0002d3f500 ffff8800b4fd4000 0000000000000000 ffff8800b4fd4000
 ffffffff82dea4d0 ffff8801d02e7ca8 ffffffff814fd953 ffff8800b4fd4000
Call Trace:
 [<ffffffff81d054ed>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d054ed>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fd953>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fde65>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fde65>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fdfa4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8346680e>] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82dff42a>] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447
 [<ffffffff82dff8f7>] __sk_free+0x57/0x230 net/core/sock.c:1480
 [<ffffffff82dffb00>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff834676ca>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff834676ca>] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82dea37d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82dea4e6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522f93>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff815234b5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bb54>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff81003625>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff81003625>] exit_to_usermode_loop+0x145/0x170 arch/x86/entry/common.c:251
 [<ffffffff81006545>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81006545>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347
 [<ffffffff8377635d>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 3760:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc9c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fcc8d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fcc8d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f8f64>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff834604c9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff834604c9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff834604c9>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff83464b5c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82deed36>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82df15a4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff837761d9>] entry_SYSCALL_64_fastpath+0x16/0x92

Freed by task 3761:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc9c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fd2e2>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fd2e2>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f9d6c>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f9d6c>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f9d6c>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f9d6c>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff8345ca50>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345f301>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345f301>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345fe6b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336e6b1>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82e014cb>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff8336d665>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831d16da>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f6f90>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82dea37d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82dea4e6>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522f93>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff815234b5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118bb54>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff81003625>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff81003625>] exit_to_usermode_loop+0x145/0x170 arch/x86/entry/common.c:251
 [<ffffffff81006545>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81006545>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347
 [<ffffffff8377635d>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800b4fd4000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b4fd4000, ffff8800b4fd4200)
The buggy address belongs to the page:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 3308 at kernel/locking/lockdep.c:3190 __lock_acquire+0x23b3/0x4b50 kernel/locking/lockdep.c:3190()
DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS)