linux-kernel - Re: [PATCH net] selftests: net: csum: Fix checksums for packets with non-zero padding

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]

Message-ID: <66e0b39776d60_cbc9e2947f@willemb.c.googlers.com.notmuch>
Date: Tue, 10 Sep 2024 17:01:11 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Sean Anderson <sean.anderson@...ux.dev>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, 
 "David S . Miller" <davem@...emloft.net>, 
 Paolo Abeni <pabeni@...hat.com>, 
 netdev@...r.kernel.org, 
 Willem de Bruijn <willemb@...gle.com>, 
 linux-kernel@...r.kernel.org, 
 Shuah Khan <shuah@...nel.org>, 
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net] selftests: net: csum: Fix checksums for packets with
 non-zero padding

Sean Anderson wrote:
> On 9/10/24 13:42, Willem de Bruijn wrote:
> > Sean Anderson wrote:
> >> On 9/9/24 21:01, Willem de Bruijn wrote:
> >> > Jakub Kicinski wrote:
> >> >> On Mon, 09 Sep 2024 13:26:42 -0400 Willem de Bruijn wrote:
> >> >> > > This seems to be a bug in the driver.
> >> >> > > 
> >> >> > > A call to skb_put_padto(skb, ETH_ZLEN) should be added.  
> >> >> > 
> >> >> > In which case this test detecting it may be nice to have, for lack of
> >> >> > a more targeted test.
> >> >> 
> >> >> IIUC we're basically saying that we don't need to trim because pad
> >> >> should be 0? In that case maybe let's keep the patch but add a check 
> >> >> on top which scans the pad for non-zero bytes, and print an informative
> >> >> warning?
> >> > 
> >> > Data arriving with padding probably deserves a separate test.
> >> > 
> >> > We can use this csum test as stand-in, I suppose.
> >> > 
> >> > Is it safe to assume that all padding is wrong on ingress, not just
> >> > non-zero padding. The ip stack itself treats it as benign and trims
> >> > the trailing bytes silently.
> >> > 
> >> > I do know of legitimate cases of trailer data lifting along.
> >> 
> >> Ideally we would test that
> >> 
> >> - Ingress padding is ignored.
> > 
> > I think the goal of a hardware padding test is to detect when padding
> > leaks onto the wire.
> 
> Which is the subject of my second bullet.
> 
> > If not adding a new test, detect in csum and fail anytime padding is
> > detected (i.e., not only non-zero)?
> 
> As noted below, this is only a problem if we leak kernel memory in the
> padding. Otherwise, any kind of padding at all is completely standard
> conformant.

Ack. I actually was not clear on that.