general protection fault in fib6_purge_rt (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c543cb4a ipv4: ensure rcu_read_lock() in ipv4_link_failure()
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=17fd659f200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4fb64439e07a1ec0
dashboard link: https://syzkaller.appspot.com/bug?extid=d53d5d9b6793dc70eb9d
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+d53d5d9b6793dc70eb9d@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 30586 Comm: syz-executor.3 Not tainted 5.1.0-rc4+ #166
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:924 [inline]
RIP: 0010:fib6_purge_rt+0x4b3/0x670 net/ipv6/ip6_fib.c:960
Code: 0f b6 35 8f df 43 03 31 ff 44 89 f6 e8 a6 f7 59 fb 45 84 f6 0f 84 b3  
00 00 00 e8 58 f6 59 fb 49 8d 7f 70 48 89 f8 48 c1 e8 03 <80> 3c 18 00 0f  
85 64 01 00 00 48 89 f8 4d 8b 77 70 48 c1 e8 03 80
RSP: 0018:ffff8880549fefa8 EFLAGS: 00010203
RAX: 0000000000000020 RBX: dffffc0000000000 RCX: ffffc9000c42e000
RDX: 0000000000040000 RSI: ffffffff861698a8 RDI: 0000000000000104
RBP: ffff8880549ff000 R08: ffff88808e5a0140 R09: ffffed1011ad04be
R10: ffffed1011ad04bd R11: ffff88808d6825ef R12: 0000000000000001
R13: ffff88808d6825c0 R14: 0000000000000001 R15: 0000000000000094
FS:  00007f90dbdce700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020651000 CR3: 00000000905bd000 CR4: 00000000001406e0
Call Trace:
 fib6_del_route net/ipv6/ip6_fib.c:1813 [inline]
 fib6_del+0xac2/0x10a0 net/ipv6/ip6_fib.c:1844
 fib6_clean_node+0x3a8/0x590 net/ipv6/ip6_fib.c:2006
 fib6_walk_continue+0x495/0x900 net/ipv6/ip6_fib.c:1928
 fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1976
 fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2055
 __fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2071
 fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2082
 rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4053
 rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4058
 addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3705
 addrconf_notify+0x19a/0x2260 net/ipv6/addrconf.c:3630
 notifier_call_chain+0xc7/0x240 kernel/notifier.c:93
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:401
 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:7623
 dev_change_flags+0x10d/0x170 net/core/dev.c:7659
 devinet_ioctl+0xde6/0x1cf0 net/ipv4/devinet.c:1104
 inet_ioctl+0x2d4/0x410 net/ipv4/af_inet.c:954
 sock_do_ioctl+0xde/0x300 net/socket.c:1037
 sock_ioctl+0x32b/0x610 net/socket.c:1168
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xd6e/0x1390 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+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458c29
Code: ad b8 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 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f90dbdcdc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458c29
RDX: 0000000020000040 RSI: 0000000000008914 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f90dbdce6d4
R13: 00000000004c44a2 R14: 00000000004d7d48 R15: 00000000ffffffff
Modules linked in:
---[ end trace ee9d5c7f957c3ef2 ]---
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:924 [inline]
RIP: 0010:fib6_purge_rt+0x4b3/0x670 net/ipv6/ip6_fib.c:960
Code: 0f b6 35 8f df 43 03 31 ff 44 89 f6 e8 a6 f7 59 fb 45 84 f6 0f 84 b3  
00 00 00 e8 58 f6 59 fb 49 8d 7f 70 48 89 f8 48 c1 e8 03 <80> 3c 18 00 0f  
85 64 01 00 00 48 89 f8 4d 8b 77 70 48 c1 e8 03 80
RSP: 0018:ffff8880549fefa8 EFLAGS: 00010203
RAX: 0000000000000020 RBX: dffffc0000000000 RCX: ffffc9000c42e000
RDX: 0000000000040000 RSI: ffffffff861698a8 RDI: 0000000000000104
RBP: ffff8880549ff000 R08: ffff88808e5a0140 R09: ffffed1011ad04be
R10: ffffed1011ad04bd R11: ffff88808d6825ef R12: 0000000000000001
R13: ffff88808d6825c0 R14: 0000000000000001 R15: 0000000000000094
FS:  00007f90dbdce700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020651000 CR3: 00000000905bd000 CR4: 00000000001406e0


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