linux-kernel - Re: Linux 2.6.20-rc7

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Date:	Wed, 31 Jan 2007 22:10:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	"S.ÃaÄlar Onur" <caglar@...dus.org.tr>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Mark Huang <mlhuang@...Princeton.EDU>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: Linux 2.6.20-rc7

Linus Torvalds wrote:
> 
> On Wed, 31 Jan 2007, H. Peter Anvin wrote:
>> It would be interesting to know what the inode numbers are in the image; also,
>> what is the exact behaviour -- do you end up with a missing link, or do both
>> entries end up getting hard-linked to an empty file?
> 
> Judging by the
> 
> 	request_module: runaway loop modprobe binfmt-0000
> 
> one or more of the hardlinked binaries (modprobe being one, but not 
> necessarily the one that initially triggers hits) will read all zeroes-
> 
> Or at least bytes at offsets 2 and 3 will read as zero, causing it to not 
> be recognized as a proper binary, causing that "binfmt-0000" thing.
> 

Or perhaps not read at all, which would explain the problem.

cpio represents a hard link as who headers with the same type and the 
same file (inode) number and a link count that is > 1.  Only the first 
one contains data; the subsequent ones have length 0.  It's fairly easy 
for a bug in the decoder to truncate the file upon encountering the 
second header, since this is somewhat of a special case (it would have 
been better if the cpio format distinguished "hard link" explicitly, as 
tar does.)

I will look into this as soon as I can, but as I'm currently in the 
middle of job hunting it might take until the weekend.

	-hpa
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