general protection fault in fib_dump_info (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    da2968ff Merge tag 'pci-v5.9-fixes-1' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=137316ca900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0437fdd630bee11
dashboard link: https://syzkaller.appspot.com/bug?extid=a61aa19b0c14c8770bd9
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12707051900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1150a046900000

The issue was bisected to:

commit 0b5e2e39739e861fa5fc84ab27a35dbe62a15330
Author: David Ahern <dsahern@xxxxxxxxx>
Date:   Tue May 26 18:56:16 2020 +0000

    nexthop: Expand nexthop_is_multipath in a few places

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=139cec66900000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=105cec66900000
console output: https://syzkaller.appspot.com/x/log.txt?x=179cec66900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a61aa19b0c14c8770bd9@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 0b5e2e39739e ("nexthop: Expand nexthop_is_multipath in a few places")

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: 6830 Comm: syz-executor644 Not tainted 5.9.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:nexthop_is_blackhole include/net/nexthop.h:240 [inline]
RIP: 0010:fib_dump_info+0x893/0x1f00 net/ipv4/fib_semantics.c:1781
Code: 3c 02 00 0f 85 83 15 00 00 4d 8b 6d 10 e8 85 f1 ab fa 49 8d bd 80 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 62 15 00 00 4d 8b ad 80 00 00 00 e8 37 e2 2a 01
RSP: 0018:ffffc90001d37248 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff888093b02000 RCX: ffffffff86c84d53
RDX: 0000000000000010 RSI: ffffffff86c84d8b RDI: 0000000000000080
RBP: ffff88809f95a017 R08: 0000000000000001 R09: ffff88809f95a02b
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88809f95a000
R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880a7164a40
FS:  0000000000000000(0000) GS:ffff8880ae600000(0063) knlGS:0000000009af2840
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000020000300 CR3: 0000000099698000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rtmsg_fib+0x318/0xdf0 net/ipv4/fib_semantics.c:524
 fib_table_insert+0x1383/0x1af0 net/ipv4/fib_trie.c:1284
 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: 0023:0xf7f66549
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:00000000ffba6bdc EFLAGS: 00000282 ORIG_RAX: 0000000000000172
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000020000580
RDX: 0000000000000000 RSI: 00000000080ea00c 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 ca6d5d9f281019b7 ]---
RIP: 0010:nexthop_is_blackhole include/net/nexthop.h:240 [inline]
RIP: 0010:fib_dump_info+0x893/0x1f00 net/ipv4/fib_semantics.c:1781
Code: 3c 02 00 0f 85 83 15 00 00 4d 8b 6d 10 e8 85 f1 ab fa 49 8d bd 80 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 62 15 00 00 4d 8b ad 80 00 00 00 e8 37 e2 2a 01
RSP: 0018:ffffc90001d37248 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff888093b02000 RCX: ffffffff86c84d53
RDX: 0000000000000010 RSI: ffffffff86c84d8b RDI: 0000000000000080
RBP: ffff88809f95a017 R08: 0000000000000001 R09: ffff88809f95a02b
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88809f95a000
R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880a7164a40
FS:  0000000000000000(0000) GS:ffff8880ae600000(0063) knlGS:0000000009af2840
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f3f0e891000 CR3: 0000000099698000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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