linux-kernel - Re: [PATCH v2] ceph: fix posix ACL hooks

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Date:	Tue, 4 Feb 2014 08:17:26 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Whitehouse <swhiteho@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Ilya Dryomov <ilya.dryomov@...tank.com>,
	Sage Weil <sage@...tank.com>, Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ceph-devel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Guangliang Zhao <lucienchao@...il.com>,
	Li Wang <li.wang@...ntykylin.com>, zheng.z.yan@...el.com
Subject: Re: [PATCH v2] ceph: fix posix ACL hooks

On Tue, Feb 4, 2014 at 3:33 AM, Steven Whitehouse <swhiteho@...hat.com> wrote:
>
> The other question that I have relating to that side of things, is why
> security_inode_permission() is called from __inode_permission() rather
> than from generic_permission() ? Maybe there is a good reason, but I
> can't immediately see what it is at the moment.

"generic_permission()" is just a helper that implements the default
UNIX permissions, and won't necessarily even be called. A filesystem
could decide not to call it at all, and in fact there are cases that
don't (eg coda or the bad_inode case).

The inode_permission() class of helpers, in contrast, is what gets
called by the VFS layer itself. So if you want to catch all permission
checks (and that would be security_inode_permission()) then you need
to catch it there.

                     Linus
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