KASAN: user-memory-access Write in fib6_purge_rt (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    58e8b370 Merge branch 'net-phy-dp83867-add-some-fixes'
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=17bb8b9aa00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fc045131472947d7
dashboard link: https://syzkaller.appspot.com/bug?extid=420d3f70afb5d69d5a96
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+420d3f70afb5d69d5a96@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: user-memory-access in fib6_drop_pcpu_from  
net/ipv6/ip6_fib.c:925 [inline]
BUG: KASAN: user-memory-access in fib6_purge_rt+0x1b3/0x5e0  
net/ipv6/ip6_fib.c:937
Write of size 8 at addr 000000000000ebb4 by task syz-executor.3/14149

CPU: 0 PID: 14149 Comm: syz-executor.3 Not tainted 5.2.0-rc1+ #33
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 __kasan_report.cold+0x5/0x40 mm/kasan/report.c:321
 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_notify_flags+0x1e9/0x2c0 net/core/dev.c:7628
 dev_change_flags+0x10d/0x170 net/core/dev.c:7664
 devinet_ioctl+0x138a/0x1c50 net/ipv4/devinet.c:1104
 inet_ioctl+0x1f4/0x340 net/ipv4/af_inet.c:952
 sock_do_ioctl+0xd8/0x2f0 net/socket.c:1049
 sock_ioctl+0x3ed/0x780 net/socket.c:1200
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459279
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f79b318dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459279
RDX: 0000000020000080 RSI: 0000000000008914 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f79b318e6d4
R13: 00000000004c4c76 R14: 00000000004d89b8 R15: 00000000ffffffff
==================================================================


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