[v6.1] BUG: unable to handle kernel paging request in fib_lookup_good_nhc

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f89b6e15694c Linux 6.1.149
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=133c6312580000
kernel config: https://syzkaller.appspot.com/x/.config?x=14ab74c2f2001221
dashboard link: https://syzkaller.appspot.com/bug?extid=3450574b1b7be58482ed
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0237d8952449/disk-f89b6e15.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dadca8dfa94c/vmlinux-f89b6e15.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c73158507817/Image-f89b6e15.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+345057...@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff800000000067
KASAN: null-ptr-deref in range [0x0000000000000338-0x000000000000033f]
Mem abort info:
ESR = 0x0000000096000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x06: level 2 translation fault
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0
[dfff800000000067] address between user and kernel address ranges
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 11836 Comm: syz.5.2245 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : ip_ignore_linkdown include/linux/inetdevice.h:259 [inline]
pc : fib_lookup_good_nhc+0x84/0x360 net/ipv4/fib_trie.c:1413
lr : fib_lookup_good_nhc+0x60/0x360 net/ipv4/fib_trie.c:1410
sp : ffff8000222e72a0
x29: ffff8000222e72a0 x28: 0000000000000000 x27: dfff800000000000
x26: 1fffe0001a037b46 x25: dfff800000000000 x24: 1fffe0001e352361
x23: 0000000000000338 x22: ffff0000d01bda37 x21: 0000000000000001
x20: ffff0000c32f2a48 x19: ffff0000d01bda20 x18: 0000000000000000
x17: 0000000000000000 x16: ffff8000082d0e24 x15: 0000000000000002
x14: 0000000000000008 x13: 1ffff00002a180b1 x12: 0000000000ff0100
x11: ff0080001057d1d4 x10: 0000000000000002 x9 : ffff0000fe913780
x8 : 0000000000000067 x7 : ffff8000105cdba4 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000222e73f4
x2 : ffff0000c32f2a48 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
ip_ignore_linkdown include/linux/inetdevice.h:259 [inline]
fib_lookup_good_nhc+0x84/0x360 net/ipv4/fib_trie.c:1413
nexthop_get_nhc_lookup+0x19c/0x3c8 include/net/nexthop.h:405
fib_table_lookup+0xe88/0x1798 net/ipv4/fib_trie.c:1590
fib4_rule_action+0x1d8/0x300 net/ipv4/fib_rules.c:136
fib_rules_lookup+0x558/0xa64 net/core/fib_rules.c:318
__fib_lookup+0xe4/0x1c8 net/ipv4/fib_rules.c:93
fib_lookup+0x70/0x40c include/net/ip_fib.h:377
ip_route_output_key_hash_rcu+0x220/0x1e28 net/ipv4/route.c:2780
ip_route_output_key_hash+0x1a8/0x2ec net/ipv4/route.c:2670
__ip_route_output_key include/net/route.h:137 [inline]
ip_route_connect include/net/route.h:324 [inline]
tcp_v4_connect+0x4e4/0x1424 net/ipv4/tcp_ipv4.c:243
__inet_stream_connect+0x1fc/0xc3c net/ipv4/af_inet.c:668
inet_stream_connect+0x74/0xb0 net/ipv4/af_inet.c:739
__sys_connect_file net/socket.c:2011 [inline]
__sys_connect+0x264/0x28c net/socket.c:2028
__do_sys_connect net/socket.c:2038 [inline]
__se_sys_connect net/socket.c:2035 [inline]
__arm64_sys_connect+0x7c/0x94 net/socket.c:2035
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
Code: 960d65cc f9400268 910ce117 d343fee8 (38796908)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: 960d65cc bl 0xfffffffff8359730
4: f9400268 ldr x8, [x19]
8: 910ce117 add x23, x8, #0x338
c: d343fee8 lsr x8, x23, #3
* 10: 38796908 ldrb w8, [x8, x25] <-- trapping instruction


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