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BUG: KASAN: slab-out-of-bounds in ip6_dst_idev include/net/ip6_fib.h:187 [inline]
BUG: KASAN: slab-out-of-bounds in ip6_xmit+0x2048/0x2090 net/ipv6/ip6_output.c:256
Read of size 8 at addr ffff8801c26f4f18 by task syz-executor4/6146

CPU: 1 PID: 6146 Comm: syz-executor4 Not tainted 4.15.0-rc8+ #271
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+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 ip6_dst_idev include/net/ip6_fib.h:187 [inline]
 ip6_xmit+0x2048/0x2090 net/ipv6/ip6_output.c:256
 inet6_csk_xmit+0x2fc/0x580 net/ipv6/inet6_connection_sock.c:139
 l2tp_xmit_core net/l2tp/l2tp_core.c:1105 [inline]
 l2tp_xmit_skb+0x1068/0x1410 net/l2tp/l2tp_core.c:1200
 pppol2tp_sendmsg+0x470/0x670 net/l2tp/l2tp_ppp.c:341
 sock_sendmsg_nosec net/socket.c:638 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:648
 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2028
 __sys_sendmsg+0xe5/0x210 net/socket.c:2062
 SYSC_sendmsg net/socket.c:2073 [inline]
 SyS_sendmsg+0x2d/0x50 net/socket.c:2069
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452ee9
RSP: 002b:00007f0de91f7c58 EFLAGS: 00000212 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ee9
RDX: 0000000000000081 RSI: 000000002037ffc8 RDI: 0000000000000015
RBP: 0000000000000624 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f8400
R13: 00000000ffffffff R14: 00007f0de91f86d4 R15: 0000000000000000

Allocated by task 6146:
 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:551
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3544
 dst_alloc+0x11f/0x1a0 net/core/dst.c:107
 rt_dst_alloc+0xe9/0x540 net/ipv4/route.c:1500
 __mkroute_output net/ipv4/route.c:2242 [inline]
 ip_route_output_key_hash_rcu+0xa40/0x2c40 net/ipv4/route.c:2470
 ip_route_output_key_hash+0x20b/0x370 net/ipv4/route.c:2299
 __ip_route_output_key include/net/route.h:125 [inline]
 ip_route_connect include/net/route.h:300 [inline]
 __ip4_datagram_connect+0xa6d/0x1240 net/ipv4/datagram.c:51
 __ip6_datagram_connect+0xbaf/0xf90 net/ipv6/datagram.c:196
 ip6_datagram_connect+0x2f/0x50 net/ipv6/datagram.c:274
 inet_dgram_connect+0x16b/0x1f0 net/ipv4/af_inet.c:541
 SYSC_connect+0x213/0x4a0 net/socket.c:1621
 SyS_connect+0x24/0x30 net/socket.c:1602
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8801c26f4dc0
 which belongs to the cache ip_dst_cache of size 216
The buggy address is located 128 bytes to the right of
 216-byte region [ffff8801c26f4dc0, ffff8801c26f4e98)
The buggy address belongs to the page:
page:ffffea000709bd00 count:1 mapcount:0 mapping:ffff8801c26f4000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c26f4000 0000000000000000 000000010000000c
raw: ffffea00070c5e20 ffffea0006a08b60 ffff8801d6fb8980 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c26f4e00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801c26f4e80: 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801c26f4f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff8801c26f4f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c26f5000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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