Re: [Xen-devel] [PATCH] make pygrub cope better with big files in guest

[M A Young <m.a.young@xxxxxxxxxxxx>]

On Wed, 16 May 2012, Ian Campbell wrote:

> On Wed, 2012-05-16 at 08:25 +0100, M A Young wrote:
> > On Wed, 16 May 2012, M A Young wrote:
> >
> > > Pygrub can use a lot of memory if the kernel or ramdisk files in a guest are
> > > very big as it reads them into memory before writing them out again to
> > > temporary files (these can legitimately be big for example the initrd.img
> > > file in a Fedora 16 install is around 130MB ).
> > >
> > > This patch allows these files to be copied in one megabyte pieces, and if it
> > > sees any write problems it delets the files and exits. It also only reads up
> > > to the first megabyte of configurations files for grub etc. to avoid problems
> > > here as well (as it is a text file it should actually be much smaller).
> > >
> > > This issue was reported by Xinli Niu in the Fedora bug report
> > > https://bugzilla.redhat.com/show_bug.cgi?id=818412 who got it a CVE reference
> > > CVE-2012-2625 .
> > I realized the first patch was flawed as I was potentially using a file
> > descriptor after I closed it. This is an untested correction.
> I think you might want a couple of closes on datafile in here. Otherwise
> it looks good to me (by inspection, I've not run it either).
I am attaching the third version of this patch. The datafile object 
doesn't have an explicit close so this patch uses del to clean it. I was 
also using unlink incorrectly which is now fixed.
I have tested it for basic functionality and also used pygrub directly to 
write to a very small file system and with this patch pygrub deletes the 
temporary files it creates if it runs out of file space.
        Michael Young

Attachment: pygrub.size.limits.patch
Description: Text document

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