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Date: Fri, 10 Jan 2014 08:18:18 +0800
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Subject: 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>,
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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