KASAN: use-after-free Read in rt6_dump_route

[syzbot]

Hello,

syzbot hit the following crash on net-next commit
564737f981fb4b4b3266901508bb9b90d9d43de8

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f87d3d...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

==================================================================
BUG: KASAN: use-after-free in rt6_dump_route+0x287/0x2f0
net/ipv6/route.c:4436
Read of size 4 at addr ffff8801ca95dc14 by task syz-executor2/9561

CPU: 1 PID: 9561 Comm: syz-executor2 Not tainted 4.15.0-rc7+ #189
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_load4_noabort+0x14/0x20 mm/kasan/report.c:429
rt6_dump_route+0x287/0x2f0 net/ipv6/route.c:4436
fib6_dump_node+0x100/0x1a0 net/ipv6/ip6_fib.c:431
fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1838
fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1886
fib6_dump_table net/ipv6/ip6_fib.c:490 [inline]
inet6_dump_fib+0x83d/0xe10 net/ipv6/ip6_fib.c:563
rtnl_dump_all+0x162/0x460 net/core/rtnetlink.c:3114
netlink_dump+0x492/0xcf0 net/netlink/af_netlink.c:2222
__netlink_dump_start+0x4f0/0x6d0 net/netlink/af_netlink.c:2319
netlink_dump_start include/linux/netlink.h:214 [inline]
rtnetlink_rcv_msg+0x7f0/0xb10 net/core/rtnetlink.c:4493
netlink_rcv_skb+0x224/0x470 net/netlink/af_netlink.c:2441
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4548
netlink_unicast_kernel net/netlink/af_netlink.c:1308 [inline]
netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1334
netlink_sendmsg+0xa4a/0xe60 net/netlink/af_netlink.c:1897
sock_sendmsg_nosec net/socket.c:630 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:640
sock_write_iter+0x31a/0x5d0 net/socket.c:909
call_write_iter include/linux/fs.h:1772 [inline]
new_sync_write fs/read_write.c:469 [inline]
__vfs_write+0x684/0x970 fs/read_write.c:482
vfs_write+0x189/0x510 fs/read_write.c:544
SYSC_write fs/read_write.c:589 [inline]
SyS_write+0xef/0x220 fs/read_write.c:581
entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452cf9
RSP: 002b:00007f4663f06c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452cf9
RDX: 0000000000000024 RSI: 000000002068cfdc RDI: 0000000000000013
RBP: 0000000000000579 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f63f8
R13: 00000000ffffffff R14: 00007f4663f076d4 R15: 0000000000000001

Allocated by task 5943:
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:104
__ip6_dst_alloc+0x35/0x90 net/ipv6/route.c:361
ip6_dst_alloc+0x29/0xb0 net/ipv6/route.c:376
ip6_route_info_create+0x4ff/0x2e20 net/ipv6/route.c:2538
ip6_route_add+0xa2/0x190 net/ipv6/route.c:2779
ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
sock_do_ioctl+0x65/0xb0 net/socket.c:958
sock_ioctl+0x2c2/0x440 net/socket.c:1055
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
entry_SYSCALL_64_fastpath+0x23/0x9a

Freed by task 8598:
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3488 [inline]
kmem_cache_free+0x83/0x2a0 mm/slab.c:3746
dst_destroy+0x257/0x370 net/core/dst.c:140
dst_destroy_rcu+0x16/0x20 net/core/dst.c:153
__rcu_reclaim kernel/rcu/rcu.h:195 [inline]
rcu_do_batch kernel/rcu/tree.c:2758 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2996
__do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801ca95db40
which belongs to the cache ip6_dst_cache of size 320
The buggy address is located 212 bytes inside of
320-byte region [ffff8801ca95db40, ffff8801ca95dc80)
The buggy address belongs to the page:
page:ffffea00072a5740 count:1 mapcount:0 mapping:ffff8801ca95d0c0
index:0xffff8801ca95d3c0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801ca95d0c0 ffff8801ca95d3c0 0000000100000008
raw: ffffea00074c1ce0 ffffea0007663b60 ffff8801d326a900 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801ca95db00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff8801ca95db80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801ca95dc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801ca95dc80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff8801ca95dd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line in the email body.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.