==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8800b5d29680 by task syzkaller230323/3476

CPU: 1 PID: 3476 Comm: syzkaller230323 Not tainted 4.4.113-ge70c132 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 1ccba3ef7d86deef ffff8801cee97c20 ffffffff81d0278d
 ffffea0002d74a00 ffff8800b5d29680 0000000000000000 ffff8800b5d29680
 ffffffff82de6370 ffff8801cee97c58 ffffffff814fd053 ffff8800b5d29680
Call Trace:
 [<ffffffff81d0278d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d0278d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fd053>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fd565>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fd565>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fd6a4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff8346219e>] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82dfb27a>] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447
 [<ffffffff82dfb747>] __sk_free+0x57/0x230 net/core/sock.c:1480
 [<ffffffff82dfb950>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff8346305a>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff8346305a>] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82de621d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de6386>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522363>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81522885>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff8100361d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100361d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:251
 [<ffffffff81007067>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81007067>] syscall_return_slowpath arch/x86/entry/common.c:347 [inline]
 [<ffffffff81007067>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
 [<ffffffff81007067>] do_fast_syscall_32+0x607/0x890 arch/x86/entry/common.c:457
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17

Allocated by task 3476:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc0c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fc38d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fc38d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f8674>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff8345be59>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8345be59>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8345be59>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff834604ec>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82deabd6>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82ded444>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d74>] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline]
 [<ffffffff81006d74>] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17

Freed by task 3477:
 [<ffffffff81035df6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fc0c3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fc9e2>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fc9e2>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814f947c>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814f947c>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814f947c>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814f947c>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff834583e0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345ac91>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345ac91>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345b7fb>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336a031>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82dfd31b>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff83368fe5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831cd12a>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f2920>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82de621d>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de6386>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff81522363>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81522885>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9d4>] task_work_run+0x104/0x180 kernel/task_work.c:115
 [<ffffffff8100361d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100361d>] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:251
 [<ffffffff81007067>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81007067>] syscall_return_slowpath arch/x86/entry/common.c:347 [inline]
 [<ffffffff81007067>] do_syscall_32_irqs_on arch/x86/entry/common.c:396 [inline]
 [<ffffffff81007067>] do_fast_syscall_32+0x607/0x890 arch/x86/entry/common.c:457
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17

The buggy address belongs to the object at ffff8800b5d29680
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800b5d29680, ffff8800b5d29880)
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: 3477 Comm: syzkaller230323 Not tainted 4.4.113-ge70c132 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d2a997c0 task.stack: ffff8801d2988000
RIP: 0010:[<ffffffff81d14b06>]  [<ffffffff81d14b06>] ____rb_erase_color lib/rbtree.c:263 [inline]
RIP: 0010:[<ffffffff81d14b06>]  [<ffffffff81d14b06>] rb_erase+0x626/0x1b60 lib/rbtree.c:429
RSP: 0018:ffff8801db207d38  EFLAGS: 00010806
RAX: ffff8801d16c7e00 RBX: ffff8801d16c7df8 RCX: 1d1a89b13fffffe4
RDX: ffffed003b6432e2 RSI: ffff8801db219710 RDI: ffffffff8148f8e9
RBP: ffff8801db207d80 R08: 1ffff1001753da49 R09: 0000000000000001
R10: 0000000000000000 R11: 1ffff1003b640f6a R12: dffffc0000000000
R13: ffffffff8148f8e1 R14: e9d44d8b0006dd9b R15: e8d44d89ffffff21
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f7797b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000020013ff8 CR3: 00000001d0a0a000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801db219c40 ffff8801d2a997c0 ffffed003a553405 ffffffff842bdb20
 ffff8801db219c40 ffff8801db219710 ffff8801db219718 0000000000000000
 0000000000000000 ffff8801db207db0 ffffffff81d20268 ffffffff842bdb20
Call Trace:
 <IRQ> 
 [<ffffffff81d20268>] timerqueue_del+0x78/0x170 lib/timerqueue.c:86
 [<ffffffff812ab4b0>] __remove_hrtimer+0x90/0x250 kernel/time/hrtimer.c:914
 [<ffffffff812ac748>] __run_hrtimer kernel/time/hrtimer.c:1234 [inline]
 [<ffffffff812ac748>] __hrtimer_run_queues+0x238/0xfe0 kernel/time/hrtimer.c:1317
 [<ffffffff812aece6>] hrtimer_interrupt+0x1a6/0x440 kernel/time/hrtimer.c:1351
 [<ffffffff810b0c7a>] local_apic_timer_interrupt+0x6a/0xb0 arch/x86/kernel/apic/apic.c:901
 [<ffffffff837747b6>] smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:925
 [<ffffffff83773710>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:737
 <EOI> 
 [<ffffffff812e2ecd>] smp_call_function_many+0x47d/0x720 kernel/smp.c:435
 [<ffffffff810ed6ae>] native_flush_tlb_others+0xfe/0x710 arch/x86/mm/tlb.c:292
 [<ffffffff810eddc3>] flush_tlb_others arch/x86/include/asm/paravirt.h:338 [inline]
 [<ffffffff810eddc3>] flush_tlb_mm_range+0x103/0x560 arch/x86/mm/tlb.c:358
 [<ffffffff81494815>] tlb_flush_mmu_tlbonly+0x185/0x2f0 mm/memory.c:242
 [<ffffffff81496c2b>] tlb_flush_mmu mm/memory.c:263 [inline]
 [<ffffffff81496c2b>] tlb_finish_mmu+0x1b/0xa0 mm/memory.c:275
 [<ffffffff814a8340>] unmap_region+0x250/0x330 mm/mmap.c:2468
 [<ffffffff814ac59f>] do_munmap+0x70f/0xec0 mm/mmap.c:2662
 [<ffffffff814af843>] mmap_region+0x423/0x1250 mm/mmap.c:1605
 [<ffffffff814b0b6d>] do_mmap+0x4fd/0x9d0 mm/mmap.c:1441
 [<ffffffff8146efee>] do_mmap_pgoff include/linux/mm.h:1915 [inline]
 [<ffffffff8146efee>] vm_mmap_pgoff+0x16e/0x1c0 mm/util.c:272
 [<ffffffff814aead0>] SYSC_mmap_pgoff mm/mmap.c:1491 [inline]
 [<ffffffff814aead0>] SyS_mmap_pgoff+0xd0/0x560 mm/mmap.c:1449
 [<ffffffff81006d74>] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline]
 [<ffffffff81006d74>] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457
 [<ffffffff837734ea>] sysenter_flags_fixed+0xd/0x17
Code: [   77.547850] PANIC: double fault, error_code: 0x0
CPU: 1 PID: 3476 Comm: syzkaller230323 Not tainted 4.4.113-ge70c132 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d2982f80 task.stack: ffff8801cee90000
RIP: 0010:[<ffffffff8148f754>]  [<ffffffff8148f754>] dump_page_badflags+0x4/0x250 mm/debug.c:84
RSP: 0018:ffff880100000000  EFLAGS: 00010046
RAX: ffff8801d2982f80 RBX: ffffea0002d74a00 RCX: ffffffff8148f8d0
RDX: 0000000000000000 RSI: ffffffff838a8de0 RDI: ffffea0002d74a00
RBP: ffff880100000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000002 R11: fffffbfff0ad7e26 R12: 0000000000000000
R13: ffffffff838a8de0 R14: 0000000000000000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0063) knlGS:00000000f77b8b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: ffff8800fffffff8 CR3: 00000001d0a0a000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:

Call Trace:
 <UNK> Code: e8 82 df 06 00 e9 83 fd ff ff e8 78 df 06 00 e9 50 fd ff ff e8 6e df 06 00 e9 1d fd ff ff 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