linux-kernel - Re: [patch] util-linux-ng: unprivileged mounts support

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Date:	Wed, 16 Jan 2008 21:33:30 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	vapier@...too.org
CC:	miklos@...redi.hu, util-linux-ng@...r.kernel.org,
	akpm@...ux-foundation.org, hch@...radead.org, serue@...ibm.com,
	viro@....linux.org.uk, kzak@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org
Subject: Re: [patch] util-linux-ng: unprivileged mounts support

> > This is an experimental patch for supporing unprivileged mounts and
> > umounts.  The following features are added:
> 
> same feedback as last time ... the cap stuff needs to be made optional and 
> proper header checks added to configure ...

Later, sure.  For now, I'm concentrating on the actual functionality.

> > 1) If mount/umount are suid, first try without privileges.
> >
> > This is done by forking, dropping privileges in child, and redirecting
> > stderr to /dev/null.  If this succeeds, then parent exits with zero
> > exit code.  Otherwise parent continues normally (with privileges).
> > This isn't perfect, because the wrong error message will be printed if
> > mount/umount failed not because of insufficient privileges, but some
> > other error (e.g. mountpoint busy).
> 
> this normalization of error information does kind of suck ... but i
> think the way it's written, the end user will still get the real
> answer the second time around when the mount is attempted with root
> privs and not stderr sent to /dev/null ?

No, for example the user will get: "only root can umount foo" instead
of "foo is busy", which is very misleading, if the user _can_ umount
foo.

Miklos
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