[syzbot] [net?] WARNING in udp_v6_send_skb

[syzbot <syzbot+ce13c07d96d04716eaa2@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    04026c998c24 net/rds: use krealloc_array() for iovector gr..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=163a6499580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f9f592a4e0cc86da
dashboard link: https://syzkaller.appspot.com/bug?extid=ce13c07d96d04716eaa2
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4f82b6352d02/disk-04026c99.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9b29e52c71b2/vmlinux-04026c99.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0b1e84e828d6/bzImage-04026c99.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ce13c07d96d04716eaa2@syzkaller.appspotmail.com

------------[ cut here ]------------
len >= 65536u
WARNING: ./include/linux/udp.h:49 at udp_set_len_short include/linux/udp.h:49 [inline], CPU#0: syz.4.4430/24120
WARNING: ./include/linux/udp.h:49 at udp_v6_send_skb+0xd3b/0x13a0 net/ipv6/udp.c:1375, CPU#0: syz.4.4430/24120
Modules linked in:
CPU: 0 UID: 0 PID: 24120 Comm: syz.4.4430 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:udp_set_len_short include/linux/udp.h:49 [inline]
RIP: 0010:udp_v6_send_skb+0xd3b/0x13a0 net/ipv6/udp.c:1375
Code: 42 0f b6 04 38 84 c0 0f 85 37 06 00 00 41 0f b7 1e e9 60 f3 ff ff e8 04 c3 43 f7 90 0f 0b 90 e9 02 f4 ff ff e8 f6 c2 43 f7 90 <0f> 0b 90 e9 e9 f4 ff ff e8 e8 c2 43 f7 90 0f 0b 90 e9 94 f5 ff ff
RSP: 0018:ffffc9000e0a74c8 EFLAGS: 00010287
RAX: ffffffff8a833e8a RBX: ffff8880355e4a00 RCX: 0000000000080000
RDX: ffffc900100ca000 RSI: 00000000000049e3 RDI: 00000000000049e4
RBP: 000000000000244c R08: ffff888049ed5d00 R09: 0000000000000003
R10: 000000000000000b R11: 0000000000000002 R12: dffffc0000000000
R13: ffff888027cb0c80 R14: 0000000000010000 R15: ffff8880355e4a02
FS:  00007f2d4a07b6c0(0000) GS:ffff888124f54000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000010000 CR3: 0000000029d28000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 udp_v6_push_pending_frames+0xa2/0x140 net/ipv6/udp.c:1451
 udpv6_sendmsg+0xfa0/0x2610 net/ipv6/udp.c:1740
 sock_sendmsg_nosec+0x90/0x180 net/socket.c:775
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmmsg+0x273/0x4d0 net/socket.c:2827
 __do_sys_sendmmsg net/socket.c:2854 [inline]
 __se_sys_sendmmsg net/socket.c:2851 [inline]
 __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2851
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2d4919de99
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:00007f2d4a07b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f2d49425fa0 RCX: 00007f2d4919de99
RDX: 0000000000000001 RSI: 0000200000006780 RDI: 0000000000000019
RBP: 00007f2d49233eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2d49426038 R14: 00007f2d49425fa0 R15: 00007ffdc2399288
 </TASK>


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