linux-kernel - Re: Pass struct vfsmount to the inode

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Date:	Sat, 26 May 2007 21:09:16 +0900
From:	Tetsuo Handa <penguin-fsdevel@...ove.SAKURA.ne.jp>
To:	agruen@...e.de, mrmacman_g4@....com
Cc:	casey@...aufler-ca.com, jmorris@...ei.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Pass struct vfsmount to the inode_create LSM hook

Hello.

Andreas Gruenbacher wrote:
> > exec { "/usr/bin/gunzip" } "gzip", "-9", "some/file/to.gz";
> The above Perl code executes /usr/bin/gunzip and sets argv[0] to "gzip", so 
> this confirms that the value of argv[0] is arbitrary. Well great, we already 
> knew.

> AppArmor does not look at argv[0] for anything, and doing so would be insane. 
> So please don't jump to the wrong conclusions.
I agree that argv[0] checking is different from pathname-based access control
or label-based access control, but I want to say argv[0] checking is still needed.

If you don't check argv[0], an attacker can request everything like

exec { "/bin/ls" } "/sbin/busybox", "cat", "/etc/shadow";
exec { "/bin/ls" } "/sbin/busybox", "rm", "/etc/shadow";

if /bin/ls and /bin/cat and /bin/rm are hardlinks of /sbin/busybox (e.g. embedded systems).

Therefore, TOMOYO Linux checks the combination of filename and argv[0] passed to execve().

Thanks.
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