netdev - Re: [PATCH -next 0/3] net: cap size to original frag size when refragmenting

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 for Android: free password hash cracker in your pocket

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

Date:	Thu, 16 Apr 2015 06:24:00 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, fw@...len.de,
	netdev@...r.kernel.org
Subject: Re: [PATCH -next 0/3] net: cap size to original frag size when
 refragmenting

On 16.04, Herbert Xu wrote:
> David Miller <davem@...emloft.net> wrote:
> > 
> > Because then there is no ambiguity at all, you preserve on output
> > exactly what you had on input.  The same geometry, the same
> > everything.  No special checks, no max frag len, none of this crap.
> > Those are all hacks trying to work around the _fundamental_ issue
> > which is that we potentially change the thing when we refrag.
> 
> Agreed.  Doing anything other than preserving the original geometry
> is simply wrong.
> 
> However, this doesn't mean that netfilter has to process each
> fragment.  What we could do is to preserve the original fragments
> in frag_list and then process the overall skb as a unit in netfilter.
> 
> On output we simply fragment according to the original frag_list.
> 
> The only thing to watch out for is to eliminate anything in the
> middle that tries to linearise the skb.

Netfilter may change the contents of the packet, even change its size.
It is *really* hard to do this while keeping the original fragments
intact.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html