==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800b4b19180 by task syzkaller699243/3331

CPU: 1 PID: 3331 Comm: syzkaller699243 Not tainted 4.4.112-g3fc4284 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 c764738d663443b5 ffff8800b4327c70 ffffffff81d054ed
 ffffea0002d2c600 ffff8800b4b19180 0000000000000000 ffff8800b4b19180
 ffffffff82dea4d0 ffff8800b4327ca8 ffffffff814fd953 ffff8800b4b19180
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 3330:
 [<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 3330:
 [<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 ffff8800b4b19180
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b4b19180, ffff8800b4b19380)
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: 0 Comm: swapper/0 Not tainted 4.4.112-g3fc4284 #32
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff84217840 task.stack: ffffffff84200000
RIP: 0010:[<ffffffff81d1661f>]  [<ffffffff81d1661f>] __rb_insert lib/rbtree.c:120 [inline]
RIP: 0010:[<ffffffff81d1661f>]  [<ffffffff81d1661f>] rb_insert_color+0x9f/0xcb0 lib/rbtree.c:420
RSP: 0018:ffff8801db207d18  EFLAGS: 00010003
RAX: 0a0508a8e82a0be9 RBX: ffffffff838a8620 RCX: ffffffff838a8620
RDX: 1ffffffff07150c5 RSI: ffff8801db219710 RDI: ffff8801db219c40
RBP: ffff8801db207d60 R08: ffffffff85808f08 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff1003b640f62 R12: ffff8800b4067df8
R13: 5028454741505f4e R14: ffff8801db219c40 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020e71000 CR3: 00000000b4aa8000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff842bcb20 ffffffff842180b0 0000000000000000 ffff8801db207d70
 ffff8801db219c40 dffffc0000000000 0000000000000000 ffff8801db219710
 ffff8800b4067e00 ffff8801db207db0 ffffffff81d22db7 ffff8801db219c58
Call Trace:
 <IRQ> 
 [<ffffffff81d22db7>] timerqueue_add+0x157/0x2a0 lib/timerqueue.c:57
 [<ffffffff812aad18>] enqueue_hrtimer+0x168/0x450 kernel/time/hrtimer.c:890
 [<ffffffff812acda2>] __run_hrtimer kernel/time/hrtimer.c:1268 [inline]
 [<ffffffff812acda2>] __hrtimer_run_queues+0x732/0xfe0 kernel/time/hrtimer.c:1317
 [<ffffffff812aee46>] hrtimer_interrupt+0x1a6/0x440 kernel/time/hrtimer.c:1351
 [<ffffffff810b0dda>] local_apic_timer_interrupt+0x6a/0xb0 arch/x86/kernel/apic/apic.c:901
 [<ffffffff83778e36>] smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:925
 [<ffffffff83777d90>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:725
 <EOI> 
 [<ffffffff81027ee5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81027ee5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:291
 [<ffffffff8102945a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:282
 [<ffffffff812204d8>] default_idle_call+0x48/0x70 kernel/sched/idle.c:93
 [<ffffffff81220be5>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff81220be5>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff81220be5>] cpu_startup_entry+0x605/0x820 kernel/sched/idle.c:301
 [<ffffffff83763159>] rest_init+0x189/0x190 init/main.c:410
 [<ffffffff84820811>] start_kernel+0x6b9/0x6ee init/main.c:682
 [<ffffffff8481f312>] x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196
 [<ffffffff8481f454>] x86_64_start_kernel+0x140/0x163 arch/x86/kernel/head64.c:185
Code: 48 89 c2 48 c1 ea 03 42 80 3c 3a 00 0f 85 94 09 00 00 4c 8b 6b 08 4d 39 e5 0f 84 b0 01 00 00 4d 85 ed 74 1d 4c 89 e8 48 c1 e8 03 <42> 80 3c 38 00 0f 85 95 09 00 00 41 f6 45 00 01 0f 84 20 03 00 
RIP  [<ffffffff81d1661f>] __rb_insert lib/rbtree.c:120 [inline]
RIP  [<ffffffff81d1661f>] rb_insert_color+0x9f/0xcb0 lib/rbtree.c:420
 RSP <ffff8801db207d18>
---[ end trace 3782e4f5f4db36e3 ]---