linux-kernel - Re: [PATCH] vfs: Fix possible NULL pointer dereference in inode

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Date:	Fri, 10 Jan 2014 07:53:41 +0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Dave Chinner <david@...morbit.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	"Theodore Ts'o" <tytso@....edu>, stable <stable@...r.kernel.org>,
	Paul Moore <paul@...l-moore.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission()

On Fri, Jan 10, 2014 at 7:37 AM, Eric Paris <eparis@...hat.com> wrote:
>
> but at least from an SELinux PoV, I think it's quick and easy, but wrong
> for maintainability...

Yeah, it's a hack, and it's wrong, and we should figure out how to do
it right. Likely we should just tie the lifetime of the i_security
member directly to the lifetime of the inode itself, and just make the
rule be that security_inode_free() gets called from whatever frees the
inode itself, and *not* have an extra rcu callback etc. But that
sounds like a bigger change than I'm comfy with right now, so the
hacky one might be the band-aid to do for stable..

The problem, of course, is that all the different filesystems have
their own inode allocations/freeing. Of course, they all tend to share
the same pattern ("call_rcu xyz_i_callback"), so maybe we could try to
make that a more generic thing? Like have a "free_inode" vfs callback,
and do the call_rcu delaying at the VFS level..

And maybe, just maybe, we could just say that that is what
"destroy_inode()" is, and that we will just call it from rcu context.
All the IO has hopefully been done earlier  Yes/no?

                 Linus
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