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BUG: KASAN: slab-out-of-bounds in ip6_dst_idev include/net/ip6_fib.h:192 [inline]
BUG: KASAN: slab-out-of-bounds in ip6_xmit+0x1f76/0x2260 net/ipv6/ip6_output.c:264
Read of size 8 at addr ffff8801d26d4018 by task syz-executor3/11116

CPU: 0 PID: 11116 Comm: syz-executor3 Not tainted 4.16.0-rc4+ #264
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23c/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 ip6_dst_idev include/net/ip6_fib.h:192 [inline]
 ip6_xmit+0x1f76/0x2260 net/ipv6/ip6_output.c:264
 inet6_csk_xmit+0x2fc/0x580 net/ipv6/inet6_connection_sock.c:139
 l2tp_xmit_core net/l2tp/l2tp_core.c:1053 [inline]
 l2tp_xmit_skb+0x105f/0x1410 net/l2tp/l2tp_core.c:1148
 pppol2tp_sendmsg+0x470/0x670 net/l2tp/l2tp_ppp.c:341
 sock_sendmsg_nosec net/socket.c:629 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:639
 SYSC_sendto+0x361/0x5c0 net/socket.c:1748
 SyS_sendto+0x40/0x50 net/socket.c:1716
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x453e69
RSP: 002b:00007f9a6034cc68 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f9a6034d6d4 RCX: 0000000000453e69
RDX: 000000000000100b RSI: 0000000020001180 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 00000000200021c0 R09: 0000000000000080
R10: 0000000000040001 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000004ca R14: 00000000006f7390 R15: 0000000000000000

Allocated by task 2:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc_node+0x144/0x760 mm/slab.c:3631
 alloc_task_struct_node kernel/fork.c:157 [inline]
 dup_task_struct kernel/fork.c:770 [inline]
 copy_process.part.38+0x19b0/0x4b60 kernel/fork.c:1631
 copy_process kernel/fork.c:1606 [inline]
 _do_fork+0x1f7/0xf70 kernel/fork.c:2087
 kernel_thread+0x34/0x40 kernel/fork.c:2146
 create_kthread kernel/kthread.c:261 [inline]
 kthreadd+0x63b/0x830 kernel/kthread.c:567
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801d26d4380
 which belongs to the cache task_struct of size 6016
The buggy address is located 872 bytes to the left of
 6016-byte region [ffff8801d26d4380, ffff8801d26d5b00)
The buggy address belongs to the page:
page:ffffea000749b500 count:1 mapcount:0 mapping:ffff8801d26d4380 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d26d4380 0000000000000000 0000000100000001
raw: ffffea00074a81a0 ffffea000749d2a0 ffff8801dad33200 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d26d3f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801d26d3f80: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d26d4000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff8801d26d4080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d26d4100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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