Re: [syzbot] [kvm?] [net?] [virt?] WARNING in virtio_transport_send_pkt_info

[syzbot <syzbot+b4d960daf7a3c7c2b7b1@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in virtio_transport_send_pkt_info

DEBUG: zerocopy_fill_skb_from_iter: final skb->len=0, skb->data_len=0
DEBUG: virtio_transport_fill_skb returned err=0, skb->len=0
------------[ cut here ]------------
'send_pkt()' returns 0, but 65536 expected
WARNING: CPU: 0 PID: 5984 at net/vmw_vsock/virtio_transport_common.c:435 virtio_transport_send_pkt_info+0xd11/0xf00 net/vmw_vsock/virtio_transport_common.c:433
Modules linked in:
CPU: 0 UID: 0 PID: 5984 Comm: syz.0.17 Not tainted 6.17.0-rc1-syzkaller-g53e760d89498-dirty #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:virtio_transport_send_pkt_info+0xd11/0xf00 net/vmw_vsock/virtio_transport_common.c:433
Code: 0f 0b 90 bd f2 ff ff ff eb bc e8 0a bf 64 f6 c6 05 ba 87 32 04 01 90 48 c7 c7 80 d8 b8 8c 44 89 f6 4c 89 ea e8 c0 4d 28 f6 90 <0f> 0b 90 90 e9 e1 fe ff ff e8 e1 be 64 f6 90 0f 0b 90 e9 c5 f7 ff
RSP: 0018:ffffc900029cf530 EFLAGS: 00010246
RAX: 3eb3238673451c00 RBX: 0000000000010000 RCX: ffff888034db0000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffffff8f879d50 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bfa1ec R12: dffffc0000000000
R13: 0000000000010000 R14: 0000000000000000 R15: ffff88804fdd20a4
FS:  00007f24a46d96c0(0000) GS:ffff88808d211000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000020000003f000 CR3: 0000000048de9000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 virtio_transport_stream_enqueue net/vmw_vsock/virtio_transport_common.c:1118 [inline]
 virtio_transport_seqpacket_enqueue+0x143/0x1c0 net/vmw_vsock/virtio_transport_common.c:846
 vsock_connectible_sendmsg+0xac7/0x1050 net/vmw_vsock/af_vsock.c:2140
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:729
 ____sys_sendmsg+0x52d/0x830 net/socket.c:2614
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
 __sys_sendmmsg+0x227/0x430 net/socket.c:2757
 __do_sys_sendmmsg net/socket.c:2784 [inline]
 __se_sys_sendmmsg net/socket.c:2781 [inline]
 __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2781
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f24a378ebe9
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:00007f24a46d9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f24a39b5fa0 RCX: 00007f24a378ebe9
RDX: 0000000000000001 RSI: 0000200000000100 RDI: 0000000000000004
RBP: 00007f24a3811e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000024008094 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f24a39b6038 R14: 00007f24a39b5fa0 R15: 00007ffcbd16bc88
 </TASK>


Tested on:

commit:         53e760d8 Merge tag 'nfsd-6.17-1' of git://git.kernel.o..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=17794af0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d67d3af29f50297e
dashboard link: https://syzkaller.appspot.com/bug?extid=b4d960daf7a3c7c2b7b1
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12ad8c34580000