linux-kernel - Re: [PATCH net-next v4] net: restore the iterator to its original state when an error occurs

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Message-ID: <tencent_922CC96DE097F8E8EAECA6CED47BCA6C840A@qq.com>
Date: Sun, 14 Dec 2025 10:49:34 +0800
From: Edward Adam Davis <eadavis@...com>
To: kuba@...nel.org
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Subject: Re: [PATCH net-next v4] net: restore the iterator to its original state when an error occurs

On Sat, 13 Dec 2025 08:37:17 +0900, Jakub Kicinski wrote:
> > In zerocopy_fill_skb_from_iter(), if two copy operations are performed
> > and the first one succeeds while the second one fails, it returns a
> > failure but the count in iterator has already been decremented due to
> > the first successful copy. This ultimately affects the local variable
> > rest_len in virtio_transport_send_pkt_info(), causing the remaining
> > count in rest_len to be greater than the actual iterator count. As a
> > result, packet sending operations continue even when the iterator count
> > is zero, which further leads to skb->len being 0 and triggers the warning
> > reported by syzbot [1].
> 
> Please address the feedback from previous revision and when you repost
> use net as the subject tag.
I have added the following explanation in the comments:
Regarding the judgment condition, I aligned it with the condition in
skb_zerocopy_iter_stream().

syzbot reported the issue in the linux-next repository, and I also
tested and created the patch using the linux-next source code repository.
Therefore, I added the subject net-next tag.
If you think adding the net subject tag directly is acceptable, I will
adjust it in the next version of the patch.