==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
Read of size 4 at addr ffff8801cfac3b80 by task syz-executor2/15521

CPU: 0 PID: 15521 Comm: syz-executor2 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 1a67fd6a13ca47d4 ffff8800b1b67a78 ffffffff81e15fed
 ffffea00073eb080 ffff8801cfac3b80 0000000000000000 ffff8801cfac3b80
 0000000000000000 ffff8800b1b67ab0 ffffffff8151b489 ffff8801cfac3b80
Call Trace:
 [<ffffffff81e15fed>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e15fed>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8151b489>] print_address_description+0x6c/0x216 mm/kasan/report.c:252
 [<ffffffff8151b7a8>] kasan_report_error mm/kasan/report.c:351 [inline]
 [<ffffffff8151b7a8>] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408
 [<ffffffff814fe714>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428
 [<ffffffff835a4b64>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830
 [<ffffffff835b166f>] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509
 [<ffffffff82f210c9>] __sock_release+0xd9/0x260 net/socket.c:592
 [<ffffffff82f21269>] sock_close+0x19/0x20 net/socket.c:1050
 [<ffffffff81528875>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81528db5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118ee4f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff81162290>] get_signal+0x1190/0x14b0 kernel/signal.c:2151
 [<ffffffff8100df4b>] do_signal+0x8b/0x1d30 arch/x86/kernel/signal.c:712
 [<ffffffff8100360a>] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:249
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349
 [<ffffffff838cc6f5>] int_ret_from_sys_call+0x25/0xa3

Allocated by task 15521:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd7d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fdab7>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fdab7>] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616
 [<ffffffff814fa1f4>] __kmalloc+0x124/0x310 mm/slub.c:3613
 [<ffffffff835a9f79>] kmalloc include/linux/slab.h:481 [inline]
 [<ffffffff835a9f79>] kzalloc include/linux/slab.h:620 [inline]
 [<ffffffff835a9f79>] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748
 [<ffffffff835aec80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27bf8>] SYSC_connect+0x1b8/0x300 net/socket.c:1570
 [<ffffffff82f2a544>] SyS_connect+0x24/0x30 net/socket.c:1551
 [<ffffffff838cc565>] entry_SYSCALL_64_fastpath+0x22/0x9e

Freed by task 15508:
 [<ffffffff81034676>] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63
 [<ffffffff814fd7d3>] save_stack+0x43/0xd0 mm/kasan/kasan.c:512
 [<ffffffff814fe102>] set_track mm/kasan/kasan.c:524 [inline]
 [<ffffffff814fe102>] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589
 [<ffffffff814fb664>] slab_free_hook mm/slub.c:1383 [inline]
 [<ffffffff814fb664>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff814fb664>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff814fb664>] kfree+0xf4/0x310 mm/slub.c:3749
 [<ffffffff835a6ee0>] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676
 [<ffffffff835a9299>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff835a9299>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff835a9dab>] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300
 [<ffffffff8349bc11>] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421
 [<ffffffff82f38add>] sk_common_release+0x6d/0x300 net/core/sock.c:2680
 [<ffffffff8349a8c5>] udp_lib_close+0x15/0x20 include/net/udp.h:190
 [<ffffffff8330244f>] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435
 [<ffffffff83424ec0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424
 [<ffffffff82f210c9>] __sock_release+0xd9/0x260 net/socket.c:592
 [<ffffffff82f21269>] sock_close+0x19/0x20 net/socket.c:1050
 [<ffffffff81528875>] __fput+0x235/0x6f0 fs/file_table.c:208
 [<ffffffff81528db5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8118ee4f>] task_work_run+0x10f/0x190 kernel/task_work.c:115
 [<ffffffff81162290>] get_signal+0x1190/0x14b0 kernel/signal.c:2151
 [<ffffffff8100df4b>] do_signal+0x8b/0x1d30 arch/x86/kernel/signal.c:712
 [<ffffffff8100360a>] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:249
 [<ffffffff81006535>] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline]
 [<ffffffff81006535>] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349
 [<ffffffff838cc6f5>] int_ret_from_sys_call+0x25/0xa3

The buggy address belongs to the object at ffff8801cfac3b80
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801cfac3b80, ffff8801cfac3d80)
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 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9a41800 task.stack: ffff8801d9a50000
RIP: 0010:[<ffffffff83456e85>]  [<ffffffff83456e85>] ipv6_get_ifaddr+0x1f5/0x510 net/ipv6/addrconf.c:1785
RSP: 0018:ffff8801db307ba8  EFLAGS: 00010246
RAX: 1ffff1001618fea7 RBX: ffff8800b0c7f400 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff83456e5e RDI: ffff8800b0c7f538
RBP: ffff8801db307c10 R08: ffff8801d9a42128 R09: 0000000000000000
R10: 0000000000000001 R11: ffff8801d9a41800 R12: dffffc0000000000
R13: ffff8801db307ca0 R14: ffff8800a56f1d40 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ea0602000 CR3: 00000000bb232000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff83456cf5 0000000000000246 ffff8800a34b8008 ffff8801db307ca8
 0000000100000002 1ffff1003b660f95 ffffed003b660f94 ffff8800b5e42200
 ffff8800b5e42200 ffff8800b5e42447 ffff8801db307ca0 ffffffff83f3e9a0
Call Trace:
 <IRQ> 
 [<ffffffff8349439c>] ndisc_send_rs+0x17c/0x430 net/ipv6/ndisc.c:616
 [<ffffffff83456967>] addrconf_rs_timer+0x287/0x5b0 net/ipv6/addrconf.c:3527
 [<ffffffff81293adc>] call_timer_fn+0x18c/0x870 kernel/time/timer.c:1185
 [<ffffffff81294802>] __run_timers kernel/time/timer.c:1261 [inline]
 [<ffffffff81294802>] run_timer_softirq+0x642/0xb90 kernel/time/timer.c:1444
 [<ffffffff838cfa7c>] __do_softirq+0x22c/0xa1a kernel/softirq.c:273
 [<ffffffff811428cd>] invoke_softirq kernel/softirq.c:350 [inline]
 [<ffffffff811428cd>] irq_exit+0x10d/0x140 kernel/softirq.c:391
 [<ffffffff838cf1e1>] exiting_irq arch/x86/include/asm/apic.h:652 [inline]
 [<ffffffff838cf1e1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:926
 [<ffffffff838ce120>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:741
 <EOI> 
 [<ffffffff81025cd5>] arch_safe_halt arch/x86/include/asm/paravirt.h:117 [inline]
 [<ffffffff81025cd5>] default_idle+0x55/0x3c0 arch/x86/kernel/process.c:432
 [<ffffffff81027be0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:423
 [<ffffffff8121ecd7>] default_idle_call+0x57/0x70 kernel/sched/idle.c:93
 [<ffffffff8121f47f>] cpuidle_idle_call kernel/sched/idle.c:157 [inline]
 [<ffffffff8121f47f>] cpu_idle_loop kernel/sched/idle.c:253 [inline]
 [<ffffffff8121f47f>] cpu_startup_entry+0x6af/0x780 kernel/sched/idle.c:301
 [<ffffffff810ac119>] start_secondary+0x329/0x400 arch/x86/kernel/smpboot.c:245
Code: e2 d6 ef fd 48 8d bb 38 01 00 00 48 89 f8 48 c1 e8 03 42 80 3c 20 00 0f 85 79 02 00 00 4c 8b bb 38 01 00 00 4c 89 fa 48 c1 ea 03 <42> 80 3c 22 00 0f 85 74 02 00 00 4d 8b 3f 49 8d bf e0 04 00 00 
RIP  [<ffffffff83456e85>] ipv6_get_ifaddr+0x1f5/0x510 net/ipv6/addrconf.c:1785
 RSP <ffff8801db307ba8>
------------[ cut here ]------------
WARNING: CPU: 1 PID: 0 at lib/list_debug.c:29 __list_add+0x120/0x1c0 lib/list_debug.c:26()
list_add corruption. next->prev should be prev (ffff8801db31fef0), but was ffff8801cfac3d80. (next=ffff8800a3149888).