Re: [syzbot] [net?] WARNING in rtmsg_ifinfo_build_skb

On Fri, Aug 14, 2026 at 5:33 PM syzbot
[off-list ref] wrote:

Hello,

syzbot found the following issue on:

HEAD commit:    02dc699f83d0 Merge tag 'kbuild-fixes-7.2-1' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17320db9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=f2f6312ad1b5a0bfe316
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d0e5b9580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f9cc9e580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-02dc699f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/faf03a1fb300/vmlinux-02dc699f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a48e50ceca1d/bzImage-02dc699f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f2f6312ad1b5a0bfe316@syzkaller.appspotmail.com

------------[ cut here ]------------
err == -EMSGSIZE
WARNING: net/core/rtnetlink.c:4538 at rtmsg_ifinfo_build_skb+0x1c1/0x260 net/core/rtnetlink.c:4538, CPU#1: syz.0.17/5924
Modules linked in:
CPU: 1 UID: 0 PID: 5924 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:rtmsg_ifinfo_build_skb+0x1c1/0x260 net/core/rtnetlink.c:4538
Code: ea 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 80 00 00 00 45 8b 76 08 e9 3c ff ff ff e8 40 d7 73 f8 90 <0f> 0b 90 ba 02 00 00 00 48 89 ee 31 ff bb a6 ff ff ff e8 d8 8f f0
RSP: 0018:ffffc90004266df0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 00000000ffffffa6 RCX: ffffffff89968a40
RDX: ffff888034e5a540 RSI: ffffffff89968aa0 RDI: ffff888034e5a540
RBP: ffff88803d24db80 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000ffffffa6 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880578ce108
FS:  000055558858a500(0000) GS:ffff8880d5ed8000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001140 CR3: 0000000036c7c000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 rtmsg_ifinfo_event net/core/rtnetlink.c:4566 [inline]
 rtmsg_ifinfo_event net/core/rtnetlink.c:4556 [inline]
 rtnetlink_event+0x137/0x1f0 net/core/rtnetlink.c:7136
 notifier_call_chain+0x99/0x3f0 kernel/notifier.c:85
 call_netdevice_notifiers_info+0xbe/0x110 net/core/dev.c:2250
 call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
 call_netdevice_notifiers net/core/dev.c:2302 [inline]
 netdev_features_change net/core/dev.c:1590 [inline]
 netdev_update_features net/core/dev.c:11108 [inline]
 netdev_update_features net/core/dev.c:11105 [inline]
 netif_disable_lro+0x3e9/0x660 net/core/dev.c:1831
 inetdev_init+0x371/0x570 net/ipv4/devinet.c:284
 inetdev_event+0x7fa/0x17f0 net/ipv4/devinet.c:1590
 notifier_call_chain+0x99/0x3f0 kernel/notifier.c:85
 call_netdevice_notifiers_info+0xbe/0x110 net/core/dev.c:2250
 call_netdevice_notifiers_extack net/core/dev.c:2288 [inline]
 call_netdevice_notifiers net/core/dev.c:2302 [inline]
 register_netdevice+0x1998/0x25a0 net/core/dev.c:11484
 macsec_newlink+0x4fb/0x1c50 drivers/net/macsec.c:4221
 rtnl_newlink_create net/core/rtnetlink.c:3913 [inline]
 __rtnl_newlink net/core/rtnetlink.c:4044 [inline]
 rtnl_newlink+0x1499/0x2380 net/core/rtnetlink.c:4159
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:7076
 netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2684
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2738
 __sys_sendmsg+0x160/0x210 net/socket.c:2770
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbf0c99e019
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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffe9eca118 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fbf0cc25fa0 RCX: 00007fbf0c99e019
RDX: 0000000000000000 RSI: 0000200000000280 RDI: 0000000000000005
RBP: 00007fbf0ca3500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbf0cc25fac R14: 00007fbf0cc25fa0 R15: 00007fbf0cc25fa0
 </TASK>


---
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diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index ee0e2eb7dbc61c1affe4b0203337f2fdaeaa031c..0844f551d3be696bad72a8322fa4ea1bf9ccf105

100644

--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c

@@ -4402,7 +4402,7 @@ static int macsec_fill_info(struct sk_buff *skb,
                csid = secy->xpn ? MACSEC_CIPHER_ID_GCM_AES_XPN_256 :

MACSEC_CIPHER_ID_GCM_AES_256;
                break;
        default:
-               goto nla_put_failure;
+               return 0;
        }

        if (nla_put_sci(skb, IFLA_MACSEC_SCI, secy->sci,