general protection fault in fib_check_nexthop

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    18445bf4 Merge tag 'spi-fix-v5.9-rc1' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=162cbd7a900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0437fdd630bee11
dashboard link: https://syzkaller.appspot.com/bug?extid=55a3e617aaf04b962a3e
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

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+55a3e617aaf04b962a3e@xxxxxxxxxxxxxxxxxxxxxxxxx

general protection fault, probably for non-canonical address 0xdffffc0000000010: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000080-0x0000000000000087]
CPU: 0 PID: 3746 Comm: syz-executor.2 Not tainted 5.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:fib_check_nexthop+0x198/0x660 net/ipv4/nexthop.c:733
Code: 48 c1 ea 03 80 3c 02 00 0f 85 7b 04 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 5b 10 48 8d bb 80 00 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 4b 04 00 00 48 8b 9b 80 00 00 00 48 b8 00 00 00
RSP: 0018:ffffc90017a0f308 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc9000cc16000
RDX: 0000000000000010 RSI: ffffffff86cbe7bd RDI: 0000000000000080
RBP: 000000000000008b R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000001 R12: ffffc90017a0f8a8
R13: 0000000000000001 R14: ffff8880a2bb7500 R15: ffffffff88ff41e0
FS:  0000000000000000(0000) GS:ffff8880ae600000(0063) knlGS:00000000f5535b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f2094027659 CR3: 000000020cbe4000 CR4: 00000000001506f0
DR0: 0000000020000080 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
 fib_create_info+0x1ae8/0x49e0 net/ipv4/fib_semantics.c:1490
 fib_table_insert+0x1c7/0x1af0 net/ipv4/fib_trie.c:1189
 inet_rtm_newroute+0x109/0x1e0 net/ipv4/fib_frontend.c:883
 rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5563
 netlink_rcv_skb+0x15a/0x430 net/netlink/af_netlink.c:2470
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:671
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2353
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2407
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2440
 do_syscall_32_irqs_on arch/x86/entry/common.c:84 [inline]
 __do_fast_syscall_32+0x57/0x80 arch/x86/entry/common.c:126
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:149
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f3b549
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f55350cc EFLAGS: 00000296 ORIG_RAX: 0000000000000172
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 1afa7bb3bbb54c93 ]---
RIP: 0010:fib_check_nexthop+0x198/0x660 net/ipv4/nexthop.c:733
Code: 48 c1 ea 03 80 3c 02 00 0f 85 7b 04 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 5b 10 48 8d bb 80 00 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 4b 04 00 00 48 8b 9b 80 00 00 00 48 b8 00 00 00
RSP: 0018:ffffc90017a0f308 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc9000cc16000
RDX: 0000000000000010 RSI: ffffffff86cbe7bd RDI: 0000000000000080
RBP: 000000000000008b R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000001 R12: ffffc90017a0f8a8
R13: 0000000000000001 R14: ffff8880a2bb7500 R15: ffffffff88ff41e0
FS:  0000000000000000(0000) GS:ffff8880ae600000(0063) knlGS:00000000f5535b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f5c1af16000 CR3: 000000020cbe4000 CR4: 00000000001506f0
DR0: 0000000020000080 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600


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