Date: Mon, 3 Feb 2014 21:39:26 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>,
        Ilya Dryomov <ilya.dryomov@inktank.com>, Sage Weil <sage@inktank.com>,
        Dave Jones <davej@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ceph-devel@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Guangliang Zhao <lucienchao@gmail.com>,
        Li Wang <li.wang@ubuntykylin.com>, zheng.z.yan@intel.com
Subject: Re: [PATCH v2] ceph: fix posix ACL hooks
Message-ID: <20140203213926.GA10323@ZenIV.linux.org.uk>
References: <CALFYKtDCNWK+9m5m3P01dcxOOV7iHFeNaOH=Q=6Pffuo8gmrMQ@mail.gmail.com>
 <1391013467-7598-1-git-send-email-ilya.dryomov@inktank.com>
 <CA+55aFwTuBDHgQoTymr8OtE-+k=+pX0T_eb+fff0K+Pa3C-g-Q@mail.gmail.com>
 <20140130075421.GA10050@infradead.org>
 <CA+55aFxbVFpy8Y8P5fMCmmTSGbFxU9dTbOj9uTH+fKWGUzwgNg@mail.gmail.com>
 <20140203102943.GF11829@infradead.org>
 <CA+55aFytvTPdBsv6BwSomUGWXZ_tKP=BxaeJ7FXBft0JNnjBCQ@mail.gmail.com>
 <20140203211955.GY10323@ZenIV.linux.org.uk>
 <CA+55aFyfPVgGXn_hSBnnVyzWn4AbZQ40MPk_AoKB_6uC6LJqPg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+55aFyfPVgGXn_hSBnnVyzWn4AbZQ40MPk_AoKB_6uC6LJqPg@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org

On Mon, Feb 03, 2014 at 01:31:19PM -0800, Linus Torvalds wrote:

> If the protocol is path-based (and it happens, and it's actually the
> *correct* thing to do for a network filesystem, rather than the
> idiotic "file handle" crap that tries to emulate the unix inode
> semantics in the protocol), then the inode is simply not sufficient.
> 
> And no, d_find_alias() is not correct or sufficient either. It can
> work in practice (and probably does perfectly fine 99.9% of the time),
> but it can equally well give the *wrong* dentry: yes, the dentry it
> returns would have been a valid dentry for somebody at some time, but
> it might be a stale dentry *now*, and it might be the wrong dentry for
> the current user (because the current user may not have permissions to
> that particular path, even if the user has permissions through his
> *own* path).
> 
> So I really think you're *fundamentally* incorrect when you say
> "result *is* a function of inode alone".

Which fs are you talking about?  For 9P it *is* a function of inode alone.
For CIFS there's no wrong dentry to pick - it doesn't have links to start
with.

If we really have hardlinks, the result of permission check would better
be a function of inode itself - as in, "if it gives different results
for two pathnames reachable for the same user, we have a bug".
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/