linux-kernel - Re: [PATCH 00/11] cross rename v3

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Date:	Tue, 14 Jan 2014 07:03:55 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mszeredi@...e.cz, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org
Cc:	miklos@...redi.hu, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	akpm@...ux-foundation.org, dhowells@...hat.com, zab@...hat.com,
	jack@...e.cz, luto@...capital.net
Subject: Re: [PATCH 00/11] cross rename v3

Miklos Szeredi wrote:
> Cross rename (A, B) is equivalent to plain rename(A, B) + plain rename
> (B, A) done as a single atomic operation.  If security module allows
> both then cross rename is allowed.  If at least one is denied then the
> cross rename is denied.

Yes, the functionality itself is fine. The problem is how LSM users check
their permissions for the functionality.

> 
> This is prepared for in "[PATCH 06/11] security: add flags to rename
> hooks" and actually done in "[PATCH 07/11] vfs: add cross-rename".
> 
> Security people are free to implement a explicit security check for
> cross rename, but I don't think that is in the scope of this patchset.
> 
I don't know how their permissions are checked, but I think that
swapping /A/B and /C/D should check not only

  Remove a name from directory A
  Add a name to directory C

but also

  Add a name to directory A
  Remove a name from directory C

using their security labels.

Without making changes to security/*/ directory, SELinux/SMACK/TOMOYO/AppArmor
might fail to check the latter permissions. Please get confirmation from LSM
people before you merge this change to linux-next tree.
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