KASAN: null-ptr-deref Write in fib6_purge_rt

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 12522281 Linux 4.19.182
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14286caad00000
kernel config: https://syzkaller.appspot.com/x/.config?x=2211c6daad8bbe0
dashboard link: https://syzkaller.appspot.com/bug?extid=f667201cc49ff981da2c

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f66720...@syzkaller.appspotmail.com

device veth0_macvtap left promiscuous mode
device veth1_vlan left promiscuous mode
device veth0_vlan left promiscuous mode
Bluetooth: hci1: command 0x0406 tx timeout
==================================================================
BUG: KASAN: null-ptr-deref in fib6_drop_pcpu_from net/ipv6/ip6_fib.c:898 [inline]
BUG: KASAN: null-ptr-deref in fib6_purge_rt+0x1ba/0x610 net/ipv6/ip6_fib.c:912
Write of size 8 at addr 00000000000001e2 by task kworker/u4:10/29375

CPU: 0 PID: 29375 Comm: kworker/u4:10 Not tainted 4.19.182-syzkaller #0
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+0x1fc/0x2ef lib/dump_stack.c:118
kasan_report_error.cold+0x15b/0x1b9 mm/kasan/report.c:352
kasan_report+0x8f/0xa0 mm/kasan/report.c:412
fib6_drop_pcpu_from net/ipv6/ip6_fib.c:898 [inline]
fib6_purge_rt+0x1ba/0x610 net/ipv6/ip6_fib.c:912
fib6_del_route net/ipv6/ip6_fib.c:1802 [inline]
fib6_del+0x9d2/0xeb0 net/ipv6/ip6_fib.c:1838
fib6_clean_node+0x35a/0x560 net/ipv6/ip6_fib.c:1999
fib6_walk_continue+0x4ff/0x8d0 net/ipv6/ip6_fib.c:1922
fib6_walk+0x182/0x370 net/ipv6/ip6_fib.c:1970
fib6_clean_tree+0xc2/0x100 net/ipv6/ip6_fib.c:2047
__fib6_clean_all+0x11f/0x2a0 net/ipv6/ip6_fib.c:2063
rt6_sync_down_dev net/ipv6/route.c:4133 [inline]
rt6_disable_ip+0xb5/0x700 net/ipv6/route.c:4138
addrconf_ifdown.isra.0+0xf6/0x1320 net/ipv6/addrconf.c:3664
addrconf_notify+0x568/0x21f0 net/ipv6/addrconf.c:3589
notifier_call_chain+0xc0/0x230 kernel/notifier.c:93
call_netdevice_notifiers net/core/dev.c:1762 [inline]
dev_close_many+0x323/0x670 net/core/dev.c:1514
rollback_registered_many+0x2f7/0xe70 net/core/dev.c:8165
unregister_netdevice_many.part.0+0x1a/0x300 net/core/dev.c:9316
unregister_netdevice_many net/core/dev.c:9315 [inline]
default_device_exit_batch+0x2fa/0x3c0 net/core/dev.c:9787
ops_exit_list+0xf9/0x150 net/core/net_namespace.c:156
cleanup_net+0x3b4/0x8b0 net/core/net_namespace.c:553
process_one_work+0x864/0x1570 kernel/workqueue.c:2152
worker_thread+0x64c/0x1130 kernel/workqueue.c:2295
kthread+0x33f/0x460 kernel/kthread.c:259
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
==================================================================


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[syzbot]

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