==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xf2/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800a0cc3b80 by task syz-executor0/17311

CPU: 0 PID: 17311 Comm: syz-executor0 Not tainted 4.4.132-g9ff3cfc #48
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 88a29856461981de ffff8800acfffc68 ffffffff81e0df8d
 ffffea0002833080 ffff8800a0cc3b80 0000000000000000 ffff8800a0cc3b80
 ffffffff82f18e30 ffff8800acfffca0 ffffffff8151526c ffff8800a0cc3b80
Call Trace:
 [<ffffffff81e0df8d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0df8d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151526c>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151558b>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151558b>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814f9064>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff835a46a2>] pppol2tp_session_destruct+0xf2/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82f2de9c>] sk_destruct+0x4c/0x4c0 net/core/sock.c:1447
 [<ffffffff82f2e46e>] __sk_free+0x15e/0x220 net/core/sock.c:1480
 [<ffffffff82f2e560>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff835a545a>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff835a545a>] pppol2tp_release+0x26a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82f18d06>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18e46>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522655>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522b95>] ____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
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348
 [<ffffffff838c03b5>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 17305:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f8133>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8417>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8417>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f4b34>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff8359dcf9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8359dcf9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8359dcf9>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835a2a00>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1d728>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f20064>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c0225>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 17305:
 [<ffffffff810341d6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814f8133>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814f8a62>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814f8a62>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f5f64>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f5f64>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f5f64>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f5f64>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff8359ac60>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff8359d019>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8359d019>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff8359db2b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff83490121>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f2e5dd>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8348edd5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff832f6aaf>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff83419640>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f18d06>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff82f18e46>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522655>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81522b95>] ____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
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348
 [<ffffffff838c03b5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8800a0cc3b80
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800a0cc3b80, ffff8800a0cc3d80)
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: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.132-g9ff3cfc #48
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9a41800 task.stack: ffff8801d9a50000
RIP: 0010:[<ffffffff81e1f041>]  [<ffffffff81e1f041>] rb_set_parent_color include/linux/rbtree_augmented.h:117 [inline]
RIP: 0010:[<ffffffff81e1f041>]  [<ffffffff81e1f041>] ____rb_erase_color lib/rbtree.c:345 [inline]
RIP: 0010:[<ffffffff81e1f041>]  [<ffffffff81e1f041>] rb_erase+0x721/0x1cb0 lib/rbtree.c:429
RSP: 0018:ffff8801db307cf8  EFLAGS: 00010086
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffff8800ac11fb20
RDX: ffffed003b6632e2 RSI: ffff8801db319710 RDI: 0000000000000000
RBP: ffff8801db307d40 R08: ffffffff8533dfd0 R09: 0000000000000001
R10: 0000000000000000 R11: ffff8801d9a41800 R12: ffff8800ac11fb10
R13: ffff8800ac11fb11 R14: ffffea0002833088 R15: ffffea0002833080
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff4a5dbc000 CR3: 00000001c1f61000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff844c64e0 ffff8801d9a41800 ffffed003b34841b ffff8801d9a420e0
 ffff8801db319c40 ffff8801db319710 ffff8801db319718 0000000000000000
 0000000000000000 ffff8801db307d70 ffffffff81e2bba8 ffffffff844bdba0
Call Trace:
 <IRQ> 
 [<ffffffff81e2bba8>] timerqueue_del+0x78/0x170 lib/timerqueue.c:86
 [<ffffffff8129ba1e>] __remove_hrtimer+0x8e/0x250 kernel/time/hrtimer.c:917
 [<ffffffff8129da4d>] __run_hrtimer kernel/time/hrtimer.c:1242 [inline]
 [<ffffffff8129da4d>] __hrtimer_run_queues+0x2dd/0x1000 kernel/time/hrtimer.c:1325
 [<ffffffff8129f291>] hrtimer_interrupt+0x1b1/0x430 kernel/time/hrtimer.c:1359
 [<ffffffff810ad5c4>] local_apic_timer_interrupt+0x74/0xa0 arch/x86/kernel/apic/apic.c:901
 [<ffffffff838c2e4c>] smp_apic_timer_interrupt+0x7c/0xa0 arch/x86/kernel/apic/apic.c:925
 [<ffffffff838c1d90>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:741
 <EOI> 
 [<ffffffff81025da5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81025da5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:290
 [<ffffffff810272f0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:281
 [<ffffffff8121b9e7>] default_idle_call+0x57/0x70 kernel/sched/idle.c:93
 [<ffffffff8121c18f>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff8121c18f>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff8121c18f>] cpu_startup_entry+0x6af/0x780 kernel/sched/idle.c:301
 [<ffffffff810aa1e4>] start_secondary+0x324/0x400 arch/x86/kernel/smpboot.c:242
Code: 15 00 00 4c 89 f7 49 89 44 24 10 48 c1 ef 03 80 3c 1f 00 0f 85 fd 14 00 00 48 89 c7 4d 89 e5 4d 89 67 08 48 c1 ef 03 49 83 cd 01 <80> 3c 1f 00 0f 85 95 0f 00 00 4c 89 e7 4c 89 28 48 c1 ef 03 80 
RIP  [<ffffffff81e1f041>] rb_set_parent_color include/linux/rbtree_augmented.h:117 [inline]
RIP  [<ffffffff81e1f041>] ____rb_erase_color lib/rbtree.c:345 [inline]
RIP  [<ffffffff81e1f041>] rb_erase+0x721/0x1cb0 lib/rbtree.c:429
 RSP <ffff8801db307cf8>
---[ end trace 8a324e1184767cb1 ]---