netdev - Re: [PATCH 1/3] [NET] Do pmtu check in transport layer

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: <461A6C7F.1030506@trash.net>
Date:	Mon, 09 Apr 2007 18:40:31 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	John Heffner <jheffner@....edu>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/3] [NET] Do pmtu check in transport layer

John Heffner wrote:
> Patrick McHardy wrote:
> 
>> This makes ping report an incorrect MTU when IPsec is used since we're
>> only accounting for the additional header_len, not the trailer_len
>> (which is not easily changeable). Additionally it will report different
>> MTUs for the first and following fragments when the socket is corked
>> because only the first fragment includes the header_len. It also can't
>> deal with things like NAT and routing by fwmark that change the route.
>> The old behaviour was that we get an ICMP frag. required with the MTU
>> of the final route, while this will always report the MTU of the
>> initially chosen route.
>>
>> For all these reasons I think it should be reverted to the old
>> behaviour.
> 
> 
> You're right, this is no good.  I think the other problems are fixable,
> but NAT really screws this.


Routing by fwmark is also unfixable and IPsec is quite hard.

> Unfortunately, there is still a real problem with ipv6, in that the
> output side does not generate a packet too big ICMP like ipv4.  Also, it
> feels kind of undesirable be rely on local ICMP instead of direct error
> message delivery.  I'll try to generate a new patch.


I think its necessary since at the transport layer we simply don't
have all the information about whats going to happen to a packet.
IPv6 now also supports routing by fwmark, so it has the same problem
if it doesn't generate packet too big messages.

-
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