linux-kernel - Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

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Message-ID: <20091124120906.GA1700@ucw.cz>
Date:	Tue, 24 Nov 2009 13:09:06 +0100
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Jeff Layton <jlayton@...hat.com>, jamie@...reable.org,
	ebiederm@...ssion.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk
Subject: Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks
	and file bind mounts (try #5)

On Tue 2009-11-24 12:53:09, Miklos Szeredi wrote:
> On Tue, 24 Nov 2009, Jeff Layton wrote:
> > Since it's clear that these symlinks do need to have special semantics,
> > perhaps the approach you suggest would be the best thing. I'll have to
> > think about it a bit more.
> 
> open() is not the only thing you need to think about.  Anything that
> checks read or write permission on the inode (truncate, utimes,
> *xattr) would have to be changed to respect the open mode.
> 
> See, this is not just about hacking the proc follow_symlink code to
> check some lookup intent.  It's about changing the permission checking
> mechanism for theses beasts.  And since the permission checking is
> inode based, this is not at all trivial to do.
> 
> I still believe leaving the current semantics and documenting them is
> the best option.

I believe that current semantics is ugly enough that 'documenting' it
is not enough... and people want to port from other systems, too, not
expecting nasty surprises like this...
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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