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

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Date:	Thu, 9 Jan 2014 22:25:55 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Eric Paris <eparis@...hat.com>
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 05:18:09PM -0500, Eric Paris wrote:

> > 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.
> 
> We just want the same lifetime as the inode.  Allocate the security blob
> when the inode is allocated and free the security blob when the inode is
> freed.

Ultimate freeing of struct inode can easily happen outside of VFS - that's
what ->destroy_inode() is for.  Moreover, filesystem might decide to do
very odd things to it, as long as it doesn't do so without RCU delay.
So no, there's no single place to do that.
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