netdev - Re: [PATCH net-next v2] tun: Pad virtio headers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CACGkMEtN1K7jRVmZwxah1vET=p5k_Nd0cpov=R0B8sP=bjC-sA@mail.gmail.com>
Date: Fri, 21 Feb 2025 09:14:56 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Paolo Abeni <pabeni@...hat.com>, Akihiko Odaki <akihiko.odaki@...nix.com>, 
	Jonathan Corbet <corbet@....net>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
	Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko <andrew@...nix.com>, 
	Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, devel@...nix.com
Subject: Re: [PATCH net-next v2] tun: Pad virtio headers

On Thu, Feb 20, 2025 at 4:45 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Feb 20, 2025 at 08:58:38AM +0100, Paolo Abeni wrote:
> > Hi,
> >
> > On 2/15/25 7:04 AM, Akihiko Odaki wrote:
> > > tun simply advances iov_iter when it needs to pad virtio header,
> > > which leaves the garbage in the buffer as is. This will become
> > > especially problematic when tun starts to allow enabling the hash
> > > reporting feature; even if the feature is enabled, the packet may lack a
> > > hash value and may contain a hole in the virtio header because the
> > > packet arrived before the feature gets enabled or does not contain the
> > > header fields to be hashed. If the hole is not filled with zero, it is
> > > impossible to tell if the packet lacks a hash value.
> >
> > Should virtio starting sending packets only after feature negotiation?
> > In other words, can the above happen without another bug somewhere else?
>
>
> Not if this is connected with a guest with the standard virtio driver, no.
> The issue is that tun has no concept of feature negotiation,
> and we don't know who uses the vnet header feature, or why.
>
> > I guess the following question is mostly for Jason and Michael: could be
> > possible (/would it make any sense) to use a virtio_net_hdr `flags` bit
> > to explicitly signal the hash fields presence? i.e. making the actual
> > virtio_net_hdr size 'dynamic'.
>
> But it is dynamic - that is why we have TUNSETVNETHDRSZ.

Yes, tun currently only recognizes a subset of the whole virtio-net header.

Thanks