Hello,

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

So far this crash happened 18 times on mmots, net-next.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+22b2e8ffdc35d97b5942@syzkaller.appspotmail.com
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device lo entered promiscuous mode
device lo left promiscuous mode
device lo entered promiscuous mode
==================================================================
BUG: KASAN: use-after-free in fib6_ifup+0x212/0x220 net/ipv6/route.c:3573
Read of size 8 at addr ffff8801c83b2000 by task syzkaller920794/4756

CPU: 1 PID: 4756 Comm: syzkaller920794 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_load8_noabort+0x14/0x20 mm/kasan/report.c:430
  fib6_ifup+0x212/0x220 net/ipv6/route.c:3573
  fib6_clean_node+0x389/0x580 net/ipv6/ip6_fib.c:1912
  fib6_walk_continue+0x46c/0x8a0 net/ipv6/ip6_fib.c:1838
  fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1886
  fib6_clean_tree+0x1e6/0x340 net/ipv6/ip6_fib.c:1963
  __fib6_clean_all+0x1f4/0x3a0 net/ipv6/ip6_fib.c:1979
  fib6_clean_all+0x27/0x30 net/ipv6/ip6_fib.c:1990
  rt6_sync_up+0x15e/0x1c0 net/ipv6/route.c:3592
  addrconf_notify+0x3f6/0x2310 net/ipv6/addrconf.c:3490
  notifier_call_chain+0x136/0x2c0 kernel/notifier.c:93
  __raw_notifier_call_chain kernel/notifier.c:394 [inline]
  raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
  call_netdevice_notifiers_info+0x32/0x70 net/core/dev.c:1708
  call_netdevice_notifiers net/core/dev.c:1726 [inline]
  __dev_notify_flags+0x15d/0x430 net/core/dev.c:6932
  dev_change_flags+0xf5/0x140 net/core/dev.c:6968
  devinet_ioctl+0x125b/0x19e0 net/ipv4/devinet.c:1083
  inet_ioctl+0x117/0x1c0 net/ipv4/af_inet.c:904
  packet_ioctl+0x1ff/0x310 net/packet/af_packet.c:4068
  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
RIP: 0033:0x44ceb9
RSP: 002b:00007f40cf03fce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dfc24 RCX: 000000000044ceb9
RDX: 00000000208a3fe0 RSI: 0000000000008914 RDI: 000000000000005c
RBP: 00000000006dfc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffeedfab01f R14: 00007f40cf0409c0 R15: 0000000000000001

Allocated by task 4767:
  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 4756:
  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 ffff8801c83b2000
  which belongs to the cache ip6_dst_cache of size 320
The buggy address is located 0 bytes inside of
  320-byte region [ffff8801c83b2000, ffff8801c83b2140)
The buggy address belongs to the page:
page:ffffea000720ec80 count:1 mapcount:0 mapping:ffff8801c83b2000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801c83b2000 0000000000000000 000000010000000a
raw: ffffea000730d720 ffffea00071e4160 ffff8801d32c9240 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801c83b1f00: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
  ffff8801c83b1f80: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
> ffff8801c83b2000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                    ^
  ffff8801c83b2080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801c83b2100: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================


---
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