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] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 21 Nov 2014 18:46:52 +0000
From:	Ben Hutchings <>
To:	"Michael S. Tsirkin" <>
	Hannes Frederic Sowa <>,
Subject: Re: [PATCH v2 net 1/2] drivers/net: Disable UFO through virtio

On Wed, 2014-11-19 at 11:14 +0200, Michael S. Tsirkin wrote:
> On Thu, Oct 30, 2014 at 06:27:12PM +0000, Ben Hutchings wrote:
> > IPv6 does not allow fragmentation by routers, so there is no
> > fragmentation ID in the fixed header.  UFO for IPv6 requires the ID to
> > be passed separately, but there is no provision for this in the virtio
> > net protocol.
> > 
> > Until recently our software implementation of UFO/IPv6 generated a new
> > ID, but this was a bug.  Now we will use ID=0 for any UFO/IPv6 packet
> > passed through a tap, which is even worse.
> > 
> > Unfortunately there is no distinction between UFO/IPv4 and v6
> > features, so disable UFO on taps and virtio_net completely until we
> > have a proper solution.
> > 
> > We cannot depend on VM managers respecting the tap feature flags, so
> > keep accepting UFO packets but log a warning the first time we do
> > this.
> > 
> > Signed-off-by: Ben Hutchings <>
> > Fixes: 916e4cf46d02 ("ipv6: reuse ip6_frag_id from ip6_ufo_append_data")
> There's something I don't understand here. I see:
>         NETIF_F_UFO_BIT,                /* ... UDPv4 fragmentation */
> this comment is wrong then?


> The patches drastically regress performance for UDPv4 for VMs only, but
> isn't it likely many other devices based their code on this comment?

There's only one hardware driver that implements UFO (s2io), and it does
handle IPv6.

> How about we disable UFO for IPv6 globally, and put the
> flag back in?
> We can then gradually add NETIF_F_UFO6_BIT for devices that
> actually support UFO for IPv6.

Since the corresponding virtio feature bit is understood to include
UFO/IPv6, and existing VMs rely on that, I don't see what this solves.


Ben Hutchings
Beware of bugs in the above code;
I have only proved it correct, not tried it. - Donald Knuth

Download attachment "signature.asc" of type "application/pgp-signature" (812 bytes)

Powered by blists - more mailing lists