Re: [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission()

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Dave Chinner <david@fromorbit.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	James Morris <james.l.morris@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	"Theodore Ts'o" <tytso@mit.edu>, stable <stable@vger.kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <matthew@wil.cx>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] vfs: Fix possible NULL pointer dereference in inode_permission()
Date: Fri, 10 Jan 2014 08:18:18 +0800	[thread overview]
Message-ID: <CA+55aFwVNAKAqyR8gA+pewz2qSjDCq2w+NwN-vmChoMKSz-idg@mail.gmail.com> (raw)
In-Reply-To: <20140110000642.GN10323@ZenIV.linux.org.uk>

On Fri, Jan 10, 2014 at 8:06 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Sure, we can separate the simple "just do call_rcu(...->free_inode)" case
> and hit it whenever full ->free_inode is there and ->destroy_inode isn't.
> Not too pretty, but removal of tons of boilerplate might be worth doing
> that anyway.

Yeah.

> But ->destroy_inode() is still needed for cases where fs
> has its own idea of inode lifetime rules.  Again, check what XFS is doing
> in that area...

Ok, so we can't change destroy_inode, and we'd need to add a new op
for just freeing it.

Painful mainly because there are so many filesystems, but it shouldn't
be *complicated*.

> There's an extra source of headache, BTW - what about the "LSM stacking"
> crowd and their plans?

LSM stacking is a pipedream right  now anyway, isn't it? It's been
talked about for years and years, I've never seen a patch-set that is
even remotely something we'd seriously consider.

            Linus