syzbot

==================================================================
BUG: KASAN: use-after-free in fib6_drop_pcpu_from net/ipv6/ip6_fib.c:925 [inline]
BUG: KASAN: use-after-free in fib6_purge_rt+0x1b3/0x5e0 net/ipv6/ip6_fib.c:937
Write of size 8 at addr ffff8880a7b36a0b by task kworker/u4:0/6525

CPU: 1 PID: 6525 Comm: kworker/u4:0 Not tainted 5.2.0-rc1+ #25
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
 __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x123/0x190 mm/kasan/generic.c:191
 kasan_check_write+0x14/0x20 mm/kasan/common.c:100
 fib6_drop_pcpu_from net/ipv6/ip6_fib.c:925 [inline]
 fib6_purge_rt+0x1b3/0x5e0 net/ipv6/ip6_fib.c:937
 fib6_del_route net/ipv6/ip6_fib.c:1812 [inline]
 fib6_del+0xac2/0x10a0 net/ipv6/ip6_fib.c:1843
 fib6_clean_node+0x3a5/0x590 net/ipv6/ip6_fib.c:2005
 fib6_walk_continue+0x4a9/0x8e0 net/ipv6/ip6_fib.c:1927
 fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1975
 fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2054
 __fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2070
 fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2081
 rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4169
 rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4174
 addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3709
 addrconf_notify+0x5db/0x2270 net/ipv6/addrconf.c:3634
 notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
 __raw_notifier_call_chain kernel/notifier.c:396 [inline]
 raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
 call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1753
 call_netdevice_notifiers_extack net/core/dev.c:1765 [inline]
 call_netdevice_notifiers net/core/dev.c:1779 [inline]
 dev_close_many+0x33f/0x6f0 net/core/dev.c:1522
 rollback_registered_many+0x43b/0xfc0 net/core/dev.c:8193
 unregister_netdevice_many.part.0+0x1b/0x1f0 net/core/dev.c:9324
 unregister_netdevice_many+0x3b/0x50 net/core/dev.c:9323
 ip6_tnl_exit_batch_net+0x50c/0x6f0 net/ipv6/ip6_tunnel.c:2274
 ops_exit_list.isra.0+0xfc/0x150 net/core/net_namespace.c:157
 cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553
 process_one_work+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 12213:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc mm/slab.c:3326 [inline]
 kmem_cache_alloc+0x11a/0x6f0 mm/slab.c:3488
 dst_alloc+0x10e/0x200 net/core/dst.c:93
 ip6_dst_alloc+0x34/0xa0 net/ipv6/route.c:356
 icmp6_dst_alloc+0x1a9/0x660 net/ipv6/route.c:2734
 ndisc_send_skb+0xfc1/0x14a0 net/ipv6/ndisc.c:488
 ndisc_send_ns+0x3a9/0x850 net/ipv6/ndisc.c:650
 ndisc_solicit+0x2ed/0x470 net/ipv6/ndisc.c:742
 neigh_probe+0xc6/0x110 net/core/neighbour.c:1014
 __neigh_event_send+0x3a4/0x16a0 net/core/neighbour.c:1172
 neigh_event_send include/net/neighbour.h:445 [inline]
 neigh_resolve_output+0x5cf/0x970 net/core/neighbour.c:1474
 neigh_output include/net/neighbour.h:511 [inline]
 ip6_finish_output2+0x1034/0x2550 net/ipv6/ip6_output.c:120
 ip6_finish_output+0x56d/0xc20 net/ipv6/ip6_output.c:154
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip6_output+0x235/0x7f0 net/ipv6/ip6_output.c:171
 dst_output include/net/dst.h:433 [inline]
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip6_xmit+0xe35/0x20b0 net/ipv6/ip6_output.c:275
 tcp_v6_send_response+0xe53/0x1f80 net/ipv6/tcp_ipv6.c:906
 tcp_v6_send_reset+0x77a/0xf90 net/ipv6/tcp_ipv6.c:984
 tcp_v6_rcv+0x1e8f/0x3570 net/ipv6/tcp_ipv6.c:1596
 ip6_protocol_deliver_rcu+0x2fe/0x16c0 net/ipv6/ip6_input.c:401
 ip6_input_finish+0x84/0x170 net/ipv6/ip6_input.c:442
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ip6_input+0xe4/0x3f0 net/ipv6/ip6_input.c:451
 dst_input include/net/dst.h:439 [inline]
 ip6_rcv_finish+0x1de/0x310 net/ipv6/ip6_input.c:80
 NF_HOOK include/linux/netfilter.h:305 [inline]
 NF_HOOK include/linux/netfilter.h:299 [inline]
 ipv6_rcv+0x10e/0x420 net/ipv6/ip6_input.c:276
 __netif_receive_skb_one_core+0x113/0x1a0 net/core/dev.c:4990
 __netif_receive_skb+0x2c/0x1d0 net/core/dev.c:5104
 netif_receive_skb_internal+0x117/0x5c0 net/core/dev.c:5207
 napi_frags_finish net/core/dev.c:5774 [inline]
 napi_gro_frags+0xada/0xd10 net/core/dev.c:5848
 tun_get_user+0x2f3c/0x3ff0 drivers/net/tun.c:1991
 tun_chr_write_iter+0xbd/0x156 drivers/net/tun.c:2037
 call_write_iter include/linux/fs.h:1872 [inline]
 do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x184/0x610 fs/read_write.c:951
 vfs_writev+0x1b3/0x2f0 fs/read_write.c:1015
 do_writev+0x15b/0x330 fs/read_write.c:1058
 __do_sys_writev fs/read_write.c:1131 [inline]
 __se_sys_writev fs/read_write.c:1128 [inline]
 __x64_sys_writev+0x75/0xb0 fs/read_write.c:1128
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 12213:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3432 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3698
 dst_destroy+0x29e/0x3c0 net/core/dst.c:129
 dst_destroy_rcu+0x16/0x19 net/core/dst.c:142
 __rcu_reclaim kernel/rcu/rcu.h:222 [inline]
 rcu_do_batch kernel/rcu/tree.c:2092 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2310 [inline]
 rcu_core+0xba5/0x1500 kernel/rcu/tree.c:2291
 __do_softirq+0x25c/0x94c kernel/softirq.c:293

The buggy address belongs to the object at ffff8880a7b36a00
 which belongs to the cache ip6_dst_cache of size 224
The buggy address is located 11 bytes inside of
 224-byte region [ffff8880a7b36a00, ffff8880a7b36ae0)
The buggy address belongs to the page:
page:ffffea00029ecd80 refcount:1 mapcount:0 mapping:ffff88809b4f03c0 index:0xffff8880a7b363c0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002410b48 ffff88809b143d38 ffff88809b4f03c0
raw: ffff8880a7b363c0 ffff8880a7b36000 000000010000000b 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a7b36900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880a7b36980: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880a7b36a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8880a7b36a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff8880a7b36b00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================