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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 ffff8801c4d40018 by task syz-executor3/449

CPU: 0 PID: 449 Comm: syz-executor3 Not tainted 4.16.0-rc4+ #254
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
 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2047
 __sys_sendmsg+0xe5/0x210 net/socket.c:2081
 SYSC_sendmsg net/socket.c:2092 [inline]
 SyS_sendmsg+0x2d/0x50 net/socket.c:2088
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x453e69
RSP: 002b:00007fe7f1f01c68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe7f1f026d4 RCX: 0000000000453e69
RDX: 0000000000000081 RSI: 000000002037ffc8 RDI: 0000000000000017
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000004c3 R14: 00000000006f72e8 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 2787:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3743
 free_task_struct kernel/fork.c:162 [inline]
 free_task+0x148/0x1a0 kernel/fork.c:391
 __put_task_struct+0x231/0x3c0 kernel/fork.c:657
 put_task_struct include/linux/sched/task.h:96 [inline]
 delayed_put_task_struct+0xca/0x3d0 kernel/exit.c:180
 __rcu_reclaim kernel/rcu/rcu.h:172 [inline]
 rcu_do_batch kernel/rcu/tree.c:2674 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2933 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2900 [inline]
 rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2917
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801c4d40200
 which belongs to the cache task_struct of size 6016
The buggy address is located 488 bytes to the left of
 6016-byte region [ffff8801c4d40200, ffff8801c4d41980)
The buggy address belongs to the page:
page:ffffea0007135000 count:1 mapcount:0 mapping:ffff8801c4d40200 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801c4d40200 0000000000000000 0000000100000001
raw: ffffea0006e1e4a0 ffffea0007166b20 ffff8801dad33200 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c4d3ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801c4d3ff80: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801c4d40000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff8801c4d40080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c4d40100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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