linux-kernel - Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

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Message-ID: <20121107183355.GA7421@fieldses.org>
Date:	Wed, 7 Nov 2012 13:33:55 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	"Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...nvz.org" <devel@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3] SUNRPC: set desired file system root before
 connecting local transports

On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > > So you're worried that a bug in the nfs code could modify the root and
> > > then not restore it?
> > 
> > At least the link you pointed to earlier never sets it back.
> 
> This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> 
> 	+	get_fs_root(current->fs, &root);
> 	+	set_fs_root(current->fs, &transport->root);
> 	+
> 	 	status = xs_local_finish_connecting(xprt, sock);
> 	+
> 	+	set_fs_root(current->fs, &root);
> 	+	path_put(&root);
> 
> > Instead
> > of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > and not care about current->fs->root at all.
> 
> The annoyance is that the lookup happens somewhere lower down in the
> networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> need some new (internal) API.  We'd likely be the only user of that new
> API.

So, if the only drawback is really just the risk of introducing a bug
that leaves the fs_root changed--the above seems simple enough for that
not to be a great risk, right?

Is there any other hazard to doing this that people can think of?

--b.
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