linux-kernel - Re: [PATCH] SELinux: Fix possible NULL pointer dereference in selinux_inode

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Message-ID: <20140109221303.GI10323@ZenIV.linux.org.uk>
Date:	Thu, 9 Jan 2014 22:13:03 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Eric Paris <eparis@...isplace.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <james.l.morris@...cle.com>,
	Paul Moore <paul@...l-moore.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] SELinux: Fix possible NULL pointer dereference in
 selinux_inode_permission()

On Thu, Jan 09, 2014 at 10:31:55AM -0500, Eric Paris wrote:
> Didn't Al find this/something very similar.  I really hate this
> solution.  Why should every LSM try to understand the intimate
> lifetime rules of the parent subsystems?  The real problem is that
> inode_free_security() is being called while the inode is still in use.
>  While I agree with the assessment, I disagree with the solution.  Let
> me try to find where Al and Christoph talked about this....

Because LSM has stuck its fingers into the guts of those filesystems,
obviously.

Just RCU-delay freeing the damn thing and treat NULL ->i_security in
->permission() (which can happen only with MAY_NOT_BLOCK in mask) as
"return -ECHILD and let the caller deal with that".

Modifying every ->destroy_inode() is obviously wrong - there's a lot more
filesystems than LSM buggers in the tree.
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