==================================================================
BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
Read of size 4 at addr ffff8801c8520780 by task syzkaller853405/3781

CPU: 1 PID: 3781 Comm: syzkaller853405 Not tainted 4.4.115-g0e9bcc1 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 84310552212ea29c ffff8800bacc7c68 ffffffff81d03dad
 ffffea0007214800 ffff8801c8520780 0000000000000000 ffff8801c8520780
 ffffffff82de7c10 ffff8800bacc7ca0 ffffffff814fe1e3 ffff8801c8520780
Call Trace:
 [<ffffffff81d03dad>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d03dad>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff814fe1e3>] print_address_description+0x73/0x260 mm/kasan/report.c:252
 [<ffffffff814fe6f5>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff814fe6f5>] kasan_report+0x285/0x370 mm/kasan/report.c:408
 [<ffffffff814fe834>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff83464b1e>] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476
 [<ffffffff82dfcb1a>] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447
 [<ffffffff82dfcfe7>] __sk_free+0x57/0x230 net/core/sock.c:1480
 [<ffffffff82dfd1f0>] sk_free+0x30/0x40 net/core/sock.c:1491
 [<ffffffff834659da>] sock_put include/net/sock.h:1639 [inline]
 [<ffffffff834659da>] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518
 [<ffffffff82de7abd>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de7c26>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815236a3>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81523bc5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9e4>] 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
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347
 [<ffffffff837746a9>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 3780:
 [<ffffffff81035de6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd253>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fd51d>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fd51d>] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814f9804>] __kmalloc+0x124/0x320 mm/slub.c:3613
 [<ffffffff8345e7d9>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff8345e7d9>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff8345e7d9>] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744
 [<ffffffff83462e6c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82dec476>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82deece4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff8377451f>] entry_SYSCALL_64_fastpath+0x1c/0x98

Freed by task 3780:
 [<ffffffff81035de6>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd253>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdb72>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdb72>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fa60c>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fa60c>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fa60c>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fa60c>] kfree+0xfc/0x300 mm/slub.c:3749
 [<ffffffff8345ad60>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672
 [<ffffffff8345d611>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8345d611>] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279
 [<ffffffff8345e17b>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8336c641>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82dfebbb>] sk_common_release+0x6b/0x300 net/core/sock.c:2680
 [<ffffffff8336b5f5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff831cf2aa>] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff832f4eb0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82de7abd>] sock_release+0x8d/0x1e0 net/socket.c:586
 [<ffffffff82de7c26>] sock_close+0x16/0x20 net/socket.c:1037
 [<ffffffff815236a3>] __fput+0x233/0x6d0 fs/file_table.c:208
 [<ffffffff81523bc5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118b9e4>] 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
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347
 [<ffffffff837746a9>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8801c8520780
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801c8520780, ffff8801c8520980)
The buggy address belongs to the page:
kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
BUG: unable to handle kernel paging request at ffffea0007214800
IP: [<ffffea0007214800>] 0xffffea0007214800
PGD 21f7fa067 PUD 21f7f9067 PMD 800000021e0000e3 
Oops: 0011 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 3780 Comm: syzkaller853405 Not tainted 4.4.115-g0e9bcc1 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b8e000 task.stack: ffff8801d8dc0000
RIP: 0010:[<ffffea0007214800>]  [<ffffea0007214800>] 0xffffea0007214800
RSP: 0018:ffff8801db207f08  EFLAGS: 00010046
RAX: dffffc0000000000 RBX: ffff8800b7447900 RCX: ffffffff81d63b5b
RDX: 1ffff10016e88f2c RSI: ffff8801d8dc7788 RDI: ffff8800b7447900
RBP: ffff8801db207f70 R08: 0000000020e7d000 R09: 0000000000000000
R10: 0000000000000000 R11: 1ffff1003b1b8ee8 R12: ffff8801d8dc7788
R13: ffff8801d8dc7820 R14: ffff8801d8dc0000 R15: 0000000000000000
FS:  00007ff54dbf0700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffea0007214800 CR3: 00000001d9370000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81016900 0000000000000082 ffff8801db207f58 ffffffff81d63b5b
 ffffffff8122eebd ffffffff83808ca0 00000000000000a1 0000000000000000
 ffff8801d8dc7788 00000000000000a1 ffff8800b7447900 00000000000000a1
Call Trace:
 <IRQ> 
 [<ffffffff83776fd9>] do_IRQ+0x89/0x1b0 arch/x86/kernel/irq.c:239
 [<ffffffff837750a0>] common_interrupt+0xa0/0xa0 arch/x86/entry/entry_64.S:592
 <EOI> 
 [<ffffffff812e402d>] 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
 [<ffffffff81495995>] tlb_flush_mmu_tlbonly+0x185/0x2f0 mm/memory.c:242
 [<ffffffff81497dab>] tlb_flush_mmu mm/memory.c:263 [inline]
 [<ffffffff81497dab>] tlb_finish_mmu+0x1b/0xa0 mm/memory.c:275
 [<ffffffff814a94c0>] unmap_region+0x250/0x330 mm/mmap.c:2470
 [<ffffffff814ad71f>] do_munmap+0x70f/0xec0 mm/mmap.c:2664
 [<ffffffff814b09c3>] mmap_region+0x423/0x1250 mm/mmap.c:1605
 [<ffffffff814b1ced>] do_mmap+0x4fd/0x9d0 mm/mmap.c:1441
 [<ffffffff8147016e>] do_mmap_pgoff include/linux/mm.h:1915 [inline]
 [<ffffffff8147016e>] vm_mmap_pgoff+0x16e/0x1c0 mm/util.c:272
 [<ffffffff814afc50>] SYSC_mmap_pgoff mm/mmap.c:1491 [inline]
 [<ffffffff814afc50>] SyS_mmap_pgoff+0xd0/0x560 mm/mmap.c:1449
 [<ffffffff8101beb6>] SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
 [<ffffffff8101beb6>] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
 [<ffffffff8377451f>] entry_SYSCALL_64_fastpath+0x1c/0x98
Code: 00 00 00 ff ff ff ff 00 00 00 00 a0 3f 21 07 00 ea ff ff e0 a6 26 07 00 ea ff ff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <80> 40 00 00 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 
RIP  [<ffffea0007214800>] 0xffffea0007214800
 RSP <ffff8801db207f08>
CR2: ffffea0007214800
---[ end trace 1fba02464061247d ]---