[v5.15] general protection fault in fib_lookup_good_nhc

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3dea0e7f549e Linux 5.15.186
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15d993d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=918afca6cf85eccf
dashboard link: https://syzkaller.appspot.com/bug?extid=1bec090fcfa0ab7bcbb8
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b4e974189c3a/disk-3dea0e7f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/922e99f38be2/vmlinux-3dea0e7f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/59456f23f37e/bzImage-3dea0e7f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1bec09...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc000000006b: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000358-0x000000000000035f]
CPU: 1 PID: 11813 Comm: syz.7.2032 Not tainted 5.15.186-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:ip_ignore_linkdown include/linux/inetdevice.h:254 [inline]
RIP: 0010:fib_lookup_good_nhc+0x81/0x3d0 net/ipv4/fib_trie.c:1407
Code: 4c 89 24 24 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 8f a5 59 f9 41 bc 58 03 00 00 4c 03 23 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 70 a5 59 f9 4d 8b 24 24 e8 67 0c
RSP: 0018:ffffc9000301f538 EFLAGS: 00010202
RAX: 000000000000006b RBX: ffff888023563f20 RCX: ffff88804bdb0000
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff888023563f2f R08: dffffc0000000000 R09: fffffbfff1ff3619
R10: fffffbfff1ff3619 R11: 1ffffffff1ff3618 R12: 0000000000000358
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff110046ac7e5
FS: 00007f3237d326c0(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000200 CR3: 0000000050fd9000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000001000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
nexthop_get_nhc_lookup+0x1a8/0x400 include/net/nexthop.h:405
fib_table_lookup+0xe76/0x15e0 net/ipv4/fib_trie.c:1583
fib_lookup+0x192/0x400 include/net/ip_fib.h:381
ip_route_output_key_hash_rcu+0x305/0x2460 net/ipv4/route.c:2785
ip_route_output_key_hash+0x1b1/0x2e0 net/ipv4/route.c:2675
__ip_route_output_key include/net/route.h:126 [inline]
ip_route_output_flow+0x26/0x150 net/ipv4/route.c:2905
ip_route_output_key include/net/route.h:142 [inline]
sctp_v4_get_dst+0x34d/0x10d0 net/sctp/protocol.c:449
sctp_transport_route+0x107/0x2b0 net/sctp/transport.c:463
sctp_assoc_add_peer+0x615/0x15a0 net/sctp/associola.c:665
sctp_connect_new_asoc+0x300/0x690 net/sctp/socket.c:1097
__sctp_connect+0x59e/0xd20 net/sctp/socket.c:1195
__sctp_setsockopt_connectx net/sctp/socket.c:1334 [inline]
sctp_getsockopt_connectx3+0x2c0/0x440 net/sctp/socket.c:1419
sctp_getsockopt+0x3ab/0x8a0 net/sctp/socket.c:8122
__sys_getsockopt+0x206/0x430 net/socket.c:2247
__do_sys_getsockopt net/socket.c:2262 [inline]
__se_sys_getsockopt net/socket.c:2259 [inline]
__x64_sys_getsockopt+0xb1/0xc0 net/socket.c:2259
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f3239eca929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3237d32038 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007f323a0f1fa0 RCX: 00007f3239eca929
RDX: 000000000000006f RSI: 0000000000000084 RDI: 0000000000000004
RBP: 00007f3239f4cb39 R08: 0000200000000140 R09: 0000000000000000
R10: 0000200000000200 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f323a0f1fa0 R15: 00007ffeb57031e8
</TASK>
Modules linked in:
---[ end trace 732db0921737fd44 ]---
RIP: 0010:ip_ignore_linkdown include/linux/inetdevice.h:254 [inline]
RIP: 0010:fib_lookup_good_nhc+0x81/0x3d0 net/ipv4/fib_trie.c:1407
Code: 4c 89 24 24 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 8f a5 59 f9 41 bc 58 03 00 00 4c 03 23 4c 89 e0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 e7 e8 70 a5 59 f9 4d 8b 24 24 e8 67 0c
RSP: 0018:ffffc9000301f538 EFLAGS: 00010202
RAX: 000000000000006b RBX: ffff888023563f20 RCX: ffff88804bdb0000
RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff888023563f2f R08: dffffc0000000000 R09: fffffbfff1ff3619
R10: fffffbfff1ff3619 R11: 1ffffffff1ff3618 R12: 0000000000000358
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff110046ac7e5
FS: 00007f3237d326c0(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3230a25ab8 CR3: 0000000050fd9000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000001000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 4c 89 24 24 mov %r12,(%rsp)
4: 48 89 d8 mov %rbx,%rax
7: 48 c1 e8 03 shr $0x3,%rax
b: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1)
10: 74 08 je 0x1a
12: 48 89 df mov %rbx,%rdi
15: e8 8f a5 59 f9 call 0xf959a5a9
1a: 41 bc 58 03 00 00 mov $0x358,%r12d
20: 4c 03 23 add (%rbx),%r12
23: 4c 89 e0 mov %r12,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 4c 89 e7 mov %r12,%rdi
34: e8 70 a5 59 f9 call 0xf959a5a9
39: 4d 8b 24 24 mov (%r12),%r12
3d: e8 .byte 0xe8
3e: 67 addr32
3f: 0c .byte 0xc


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.