netdev - Re: [PATCH Next V2] net: restore the iterator to its original state when an error occurs

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Message-ID: <20251128093946.18c645c6@kernel.org>
Date: Fri, 28 Nov 2025 09:39:46 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+ci3edb9412aeb2e703@...kaller.appspotmail.com,
 davem@...emloft.net, edumazet@...gle.com, eperezma@...hat.com,
 horms@...nel.org, jasowang@...hat.com, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, mst@...hat.com, netdev@...r.kernel.org,
 pabeni@...hat.com, sgarzare@...hat.com, stefanha@...hat.com,
 syzbot@...ts.linux.dev, syzbot@...kaller.appspotmail.com,
 syzkaller-bugs@...glegroups.com, virtualization@...ts.linux.dev,
 xuanzhuo@...ux.alibaba.com
Subject: Re: [PATCH Next V2] net: restore the iterator to its original state
 when an error occurs

On Fri, 28 Nov 2025 21:35:57 +0800 Edward Adam Davis 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 follow the subsystem guidelines for posting patches:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html
Your patch breaks zerocopy tests.