[syzbot] [net?] WARNING in sk_skb_reason_drop

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a58f00ed24b8 net: sched: cls_api: improve the error messag..
git tree: net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=140a735f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=47cb6c16bf912470
dashboard link: https://syzkaller.appspot.com/bug?extid=52fbd90f020788ec7709
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=132804c0580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14f481a7980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d28dcea68102/disk-a58f00ed.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8ec032ea06c6/vmlinux-a58f00ed.xz
kernel image: https://storage.googleapis.com/syzbot-assets/da9b8f80c783/bzImage-a58f00ed.xz

The issue was bisected to:

commit 82d9983ebeb871cb5abd27c12a950c14c68772e1
Author: Menglong Dong <menglon...@gmail.com>
Date: Thu Nov 7 12:55:58 2024 +0000

net: ip: make ip_route_input_noref() return drop reasons

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10ae41a7980000
final oops: https://syzkaller.appspot.com/x/report.txt?x=12ae41a7980000
console output: https://syzkaller.appspot.com/x/log.txt?x=14ae41a7980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+52fbd9...@syzkaller.appspotmail.com
Fixes: 82d9983ebeb8 ("net: ip: make ip_route_input_noref() return drop reasons")

netlink: 'syz-executor371': attribute type 4 has an invalid length.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5842 at net/core/skbuff.c:1219 __sk_skb_reason_drop net/core/skbuff.c:1216 [inline]
WARNING: CPU: 0 PID: 5842 at net/core/skbuff.c:1219 sk_skb_reason_drop+0x87/0x380 net/core/skbuff.c:1241
Modules linked in:
CPU: 0 UID: 0 PID: 5842 Comm: syz-executor371 Not tainted 6.12.0-rc6-syzkaller-01362-ga58f00ed24b8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
RIP: 0010:__sk_skb_reason_drop net/core/skbuff.c:1216 [inline]
RIP: 0010:sk_skb_reason_drop+0x87/0x380 net/core/skbuff.c:1241
Code: 00 00 00 fc ff df 41 8d 9e 00 00 fc ff bf 01 00 fc ff 89 de e8 ea 9f 08 f8 81 fb 00 00 fc ff 77 3a 4c 89 e5 e8 9a 9b 08 f8 90 <0f> 0b 90 eb 5e bf 01 00 00 00 89 ee e8 c8 9f 08 f8 85 ed 0f 8e 49
RSP: 0018:ffffc90003d57078 EFLAGS: 00010293
RAX: ffffffff898c3ec6 RBX: 00000000fffbffea RCX: ffff8880347a5a00
RDX: 0000000000000000 RSI: 00000000fffbffea RDI: 00000000fffc0001
RBP: dffffc0000000000 R08: ffffffff898c3eb6 R09: 1ffff110023eb7d4
R10: dffffc0000000000 R11: ffffed10023eb7d5 R12: dffffc0000000000
R13: ffff888011f5bdc0 R14: 00000000ffffffea R15: 0000000000000000
FS: 000055557d41e380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056519d31d608 CR3: 000000007854e000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
kfree_skb_reason include/linux/skbuff.h:1263 [inline]
ip_rcv_finish_core+0xfde/0x1b50 net/ipv4/ip_input.c:424
ip_list_rcv_finish net/ipv4/ip_input.c:610 [inline]
ip_sublist_rcv+0x3b1/0xab0 net/ipv4/ip_input.c:636
ip_list_rcv+0x42b/0x480 net/ipv4/ip_input.c:670
__netif_receive_skb_list_ptype net/core/dev.c:5715 [inline]
__netif_receive_skb_list_core+0x94e/0x980 net/core/dev.c:5762
__netif_receive_skb_list net/core/dev.c:5814 [inline]
netif_receive_skb_list_internal+0xa51/0xe30 net/core/dev.c:5905
netif_receive_skb_list+0x55/0x4b0 net/core/dev.c:5957
xdp_recv_frames net/bpf/test_run.c:280 [inline]
xdp_test_run_batch net/bpf/test_run.c:361 [inline]
bpf_test_run_xdp_live+0x1b5e/0x21b0 net/bpf/test_run.c:390
bpf_prog_test_run_xdp+0x805/0x11e0 net/bpf/test_run.c:1318
bpf_prog_test_run+0x2e4/0x360 kernel/bpf/syscall.c:4266
__sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5671
__do_sys_bpf kernel/bpf/syscall.c:5760 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5758 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5758
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f18af25a8e9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffee4090af8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f18af25a8e9
RDX: 0000000000000048 RSI: 0000000020000600 RDI: 000000000000000a
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>


---
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[Hillf Danton]

On Sat, 16 Nov 2024 10:32:25 -0800

> syzbot found the following issue on:
>
> HEAD commit: a58f00ed24b8 net: sched: cls_api: improve the error messag..
> git tree: net-next

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14f481a7980000

#syz test

--- x/net/ipv4/route.c
+++ y/net/ipv4/route.c
@@ -2478,7 +2478,7 @@ ip_route_input_rcu(struct sk_buff *skb,
int our = 0;

if (!in_dev)
- return -EINVAL;
+ return reason;
our = ip_check_mc_rcu(in_dev, daddr, saddr,
ip_hdr(skb)->protocol);

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+52fbd9...@syzkaller.appspotmail.com
Tested-by: syzbot+52fbd9...@syzkaller.appspotmail.com

Tested on:

commit: 38f83a57 Merge branch 'virtio-net-support-af_xdp-zero-..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=111c52e8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e6d63a300b6a84a4

dashboard link: https://syzkaller.appspot.com/bug?extid=52fbd90f020788ec7709
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=14789378580000

Note: testing is done by a robot and is best-effort only.

[Paolo Abeni]

@Menglong Dong: could you please have a look? The repro looks
deterministic, so it should be doable to pin-point the actual, bad
drop_reason and why/which function is triggering it. My wild guess is
that an ERRNO is type-casted to drop reason instead of being converted.

Cheers,

Paolo

[Menglong Dong]

You are right, I have figured out that the "-EINVAL" is returned
by mistake in fib_validate_source().

Sorry for that, and I'm sending a fix for it.

Thanks!
Menglong Dong

> Cheers,
>
> Paolo
>