netdev - Re: [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling

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

Date:   Fri, 9 Oct 2020 14:07:44 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>, maze@...gle.com,
        lmb@...udflare.com, shaun@...era.io,
        Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com,
        eyal.birger@...il.com
Subject: Re: [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling

On Fri, Oct 09, 2020 at 01:49:14PM -0700, John Fastabend wrote:
> Jakub Kicinski wrote:
> > On Thu, 08 Oct 2020 16:08:57 +0200 Jesper Dangaard Brouer wrote:
> > > V3: Drop enforcement of MTU in net-core, leave it to drivers
> > 
> > Sorry for being late to the discussion.
> > 
> > I absolutely disagree. We had cases in the past where HW would lock up
> > if it was sent a frame with bad geometry.
> > 
> > We will not be sprinkling validation checks across the drivers because
> > some reconfiguration path may occasionally yield a bad packet, or it's
> > hard to do something right with BPF.
> 
> This is a driver bug then. As it stands today drivers may get hit with
> skb with MTU greater than set MTU as best I can tell. Generally I
> expect drivers use MTU to configure RX buffers not sure how it is going
> to be used on TX side? Any examples? I just poked around through the
> driver source to see and seems to confirm its primarily for RX side
> configuration with some drivers throwing the event down to the firmware
> for something that I can't see in the code?
> 
> I'm not suggestiong sprinkling validation checks across the drivers.
> I'm suggesting if the drivers hang we fix them.

+1

I've seen HW that hangs when certain sizes of the packet.
Like < 68 byte TX where size is one specific constant.
I don't think it's a job of the stack or the driver to deal with that.
It's firmware/hw bug.