linux-kernel - Re: Redzone overwritten with CONFIG

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Message-ID: <20080531232352.GV30402@sequoia.sous-sol.org>
Date:	Sat, 31 May 2008 16:24:03 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Eric Sesterhenn <snakebyte@....de>
Cc:	Chris Wright <chrisw@...s-sol.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, James Morris <jmorris@...ei.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vegard Nossum <vegard.nossum@...il.com>
Subject: Re: Redzone overwritten with CONFIG_SECURITY

* Chris Wright (chrisw@...s-sol.org) wrote:
> * Eric Sesterhenn (snakebyte@....de) wrote:
> > Is it possible that this was caused because a file didnt
> > get rebuild correctly? I can still reproduce it with the
> > old checkout. Sorry if this causes unessecary noise :(
> 
> I had wondered that, since data structures will grow w/ CONFIG_SECURITY
> set (like inode, for example).  I haven't encountered a Kbuild dependency
> bug in quite a while though.

Yeah, this thing is miscompiled (thanks for the vmlinux).

$ cd /tmp/CONFIG_SECURITY-mem-corruption
$ gdb -q vmlinux
(gdb) p sizeof(struct inode)
$1 = 596
(gdb) p sizeof(struct hugetlbfs_inode_info)
$2 = 592

struct hugetlbfs_inode_info {
	struct shared_policy policy;
	struct inode vfs_inode;
};
 
The hugetlbfs_inode_info structure isn't updated with the 4 extra bytes
added from CONFIG_SECURITY to struct inode.

If you're interested in more gory details, you can look at:
$ eu-readelf -winfo vmlinux > readelf-info.out

thanks,
-chris
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