linux-kernel - Re: [syzbot] [kvm?] [net?] [virt?] WARNING in virtio_transport_send_pkt

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Message-ID: <20250812061425-mutt-send-email-mst@kernel.org>
Date: Tue, 12 Aug 2025 06:15:46 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: syzbot <syzbot+b4d960daf7a3c7c2b7b1@...kaller.appspotmail.com>
Cc: davem@...emloft.net, edumazet@...gle.com, eperezma@...hat.com,
	horms@...nel.org, jasowang@...hat.com, kuba@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, pabeni@...hat.com, sgarzare@...hat.com,
	stefanha@...hat.com, syzkaller-bugs@...glegroups.com,
	virtualization@...ts.linux.dev, xuanzhuo@...ux.alibaba.com,
	Will Deacon <will@...nel.org>
Subject: Re: [syzbot] [kvm?] [net?] [virt?] WARNING in
 virtio_transport_send_pkt_info

On Tue, Aug 12, 2025 at 03:03:02AM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> WARNING in virtio_transport_send_pkt_info

OK so the issue triggers on
commit 6693731487a8145a9b039bc983d77edc47693855
Author: Will Deacon <will@...nel.org>
Date:   Thu Jul 17 10:01:16 2025 +0100

    vsock/virtio: Allocate nonlinear SKBs for handling large transmit buffers
    

but does not trigger on:

commit 8ca76151d2c8219edea82f1925a2a25907ff6a9d
Author: Will Deacon <will@...nel.org>
Date:   Thu Jul 17 10:01:15 2025 +0100

    vsock/virtio: Rename virtio_vsock_skb_rx_put()
    


Will, I suspect your patch merely uncovers a latent bug
in zero copy handling elsewhere.
Want to take a look?



> ------------[ cut here ]------------
> 'send_pkt()' returns 0, but 65536 expected
> WARNING: CPU: 0 PID: 5936 at net/vmw_vsock/virtio_transport_common.c:428 virtio_transport_send_pkt_info+0xd11/0xf00 net/vmw_vsock/virtio_transport_common.c:426
> Modules linked in:
> CPU: 0 UID: 0 PID: 5936 Comm: syz.0.17 Not tainted 6.16.0-rc6-syzkaller-00030-g6693731487a8 #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:426
> Code: 0f 0b 90 bd f2 ff ff ff eb bc e8 2a 15 74 f6 c6 05 17 6f 40 04 01 90 48 c7 c7 00 4b b7 8c 44 89 f6 4c 89 ea e8 e0 f7 37 f6 90 <0f> 0b 90 90 e9 e1 fe ff ff e8 01 15 74 f6 90 0f 0b 90 e9 c5 f7 ff
> RSP: 0018:ffffc9000cc2f530 EFLAGS: 00010246
> RAX: 72837a5a4342cf00 RBX: 0000000000010000 RCX: ffff888033218000
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
> RBP: ffffffff8f8592b0 R08: 0000000000000003 R09: 0000000000000004
> R10: dffffc0000000000 R11: fffffbfff1bfa6ec R12: dffffc0000000000
> R13: 0000000000010000 R14: 0000000000000000 R15: ffff8880406730e4
> FS:  00007fc0bd7eb6c0(0000) GS:ffff88808d230000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fd5857ec368 CR3: 00000000517cf000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  virtio_transport_stream_enqueue net/vmw_vsock/virtio_transport_common.c:1111 [inline]
>  virtio_transport_seqpacket_enqueue+0x143/0x1c0 net/vmw_vsock/virtio_transport_common.c:839
>  vsock_connectible_sendmsg+0xac4/0x1050 net/vmw_vsock/af_vsock.c:2123
>  sock_sendmsg_nosec net/socket.c:712 [inline]
>  __sock_sendmsg+0x219/0x270 net/socket.c:727
>  ____sys_sendmsg+0x52d/0x830 net/socket.c:2566
>  ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
>  __sys_sendmmsg+0x227/0x430 net/socket.c:2709
>  __do_sys_sendmmsg net/socket.c:2736 [inline]
>  __se_sys_sendmmsg net/socket.c:2733 [inline]
>  __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2733
>  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: 0033:0x7fc0bc98ebe9
> 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:00007fc0bd7eb038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 00007fc0bcbb5fa0 RCX: 00007fc0bc98ebe9
> RDX: 0000000000000001 RSI: 0000200000000100 RDI: 0000000000000004
> RBP: 00007fc0bca11e19 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000024008094 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fc0bcbb6038 R14: 00007fc0bcbb5fa0 R15: 00007ffdb7bf09f8
>  </TASK>
> 
> 
> Tested on:
> 
> commit:         66937314 vsock/virtio: Allocate nonlinear SKBs for han..
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=159d75bc580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=84141250092a114f
> 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
> 
> Note: no patches were applied.