From: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
To: Shane Hathaway <shane@hathawaymix.org>,
       Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Configure MTU via kernel DHCP
Date: Fri, 4 Feb 2005 10:06:49 +0200
User-Agent: KMail/1.5.4
References: <200502022148.00045.shane@hathawaymix.org>
In-Reply-To: <200502022148.00045.shane@hathawaymix.org>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="koi8-r"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200502041006.49912.vda@port.imtp.ilyichevsk.odessa.ua>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1616
Lines: 30

On Thursday 03 February 2005 06:47, Shane Hathaway wrote:
> The attached patch enhances the kernel's DHCP client support (in 
> net/ipv4/ipconfig.c) to set the interface MTU if provided by the DHCP server.  
> Without this patch, it's difficult to netboot on a network that uses jumbo 
> frames.  The patch is based on 2.6.10, but I'll update it to the latest 
> testing kernel if that would expedite its inclusion in the kernel.
> 
> More background: it's currently difficult to netboot on a jumbo frame network 
> because when clients try to mount the root partition, they are still 
> configured with a small MTU and therefore reject packets sent by the 
> jumbo-frame-enabled NFS server.  Linux needs to set the client MTU before 
> mounting any NFS shares.  Fortunately, the DHCP protocol already supports 
> setting the MTU; this patch just integrates that feature into the kernel.
> 
> Incidentally, ipconfig.c doesn't appear to do enough bounds checking on byte 1 
> of DHCP/BOOTP extension fields (the length field).  It looks like a malicious 
> DHCP server could mess with kernel memory that way.  I could try to fix the 
> hole, but maybe someone more experienced with this code would like to verify 
> there's a problem first.

Long term solution is to use approptiately configured initramfs or initrd image
and do above mentioned stuff in userspace.
--
vda

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/