linux-kernel - Re: (repost) Confirmation of methods for calculating requested pathname.

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Message-ID: <20080902131127.GA5951@hallyn.com>
Date:	Tue, 2 Sep 2008 08:11:27 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Kentaro Takeda <takedakn@...data.co.jp>
Cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, miklos@...redi.hu, hch@...radead.org,
	akpm@...ux-foundation.org,
	Toshiharu Harada <haradats@...data.co.jp>
Subject: Re: (repost) Confirmation of methods for calculating requested pathname.

Quoting Kentaro Takeda (takedakn@...data.co.jp):
> Al, could you answer the following question?
> 
> 
> The current Linux kernel is not designed to pass vfsmount parameter
> that is crucial for pathname-based security including AppArmor and
> TOMOYO Linux, to LSM. Though both projects have been proposing
> patches to calculate pathname, none of them have been accepted as
> you know.
> 
> To find the reason for NACK, we examined past proposals and the
> threads. And we came to understand that you oppose accessing vfsmount
> inside vfs helper functions. Is our understanding correct?
> 
> If our understanding is correct, we would like to propose a new
> method that does not require modifications to vfs helper functions.
> Attached patch is a trial of this method.
> 
> vfs helper functions are surrounded by mnt_want_write() and
> mnt_drop_write() pairs which receive "struct vfsmount" parameter

I thought Al and others (Stephen?) had made it clear that the thing to do was
add new lsm hooks there.  So whereas inode_permission takes only an inode and
ends up calling security_inode_permission, you would add a
security_path_permission() or somesuch before or after the call to
inode_permission(), where as you've noted the path is available.  You're
*close* to doing the right thing by having a helper who is called at the right
place catch the vfsmount, but you refuse to send a patch doing exactly what
has been suggested.

-serge
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