linux-kernel - Re: [PATCH] procfs: make /proc style symlinks behave like "normal" symlinks

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Date:	Thu, 19 Nov 2009 13:56:44 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Pavel Machek <pavel@....cz>
Cc:	Jeff Layton <jlayton@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] procfs: make /proc style symlinks behave like "normal" symlinks

Pavel Machek <pavel@....cz> writes:

>> > Adding all of the short comings to followlink that readlink has is a problem,
>> > especially as followlink does much better now.
>> > 
>> > At a practical level I think your changes are much easier to exploit than
>> > Pavels contrived example.
>> > 
>> > I really don't have any problems with your first patch to proc to add the
>> > missing revalidate.
>> > 
>> 
>> Thanks, that makes sense. The raciness was evident once you pointed it
>> out, so I think you're correct that we can't take this approach.
>> 
>> Adding the missing revalidations is fine, but I don't believe that
>> helps to fix Pavel's issue. I'll go back and take a more careful look
>> at the suggestion that Miklos made and see whether it makes sense to
>> implement a new FS_* flag for this, and see what it'll take to fix
>> Pavel's issue.
>
> One posibility would be to make open(/proc/XX/fd/XX) behave like
> dup(). That should solve the NFS problems, too, no?

Not for bind mounts, and the revalidate in follow_mounts is a bug regardless.

Eric
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