Re: [PATCH] Configure MTU via kernel DHCP

[Denis Vlasenko]

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

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