Re: [AppArmor 39/45] AppArmor: Profile loading and manipulation,pathname matching

From: Greg KH
Date: Fri Jun 15 2007 - 20:31:47 EST

On Fri, Jun 15, 2007 at 05:01:25PM -0700, david@xxxxxxx wrote:
> On Fri, 15 Jun 2007, Greg KH wrote:
> > On Fri, Jun 15, 2007 at 04:30:44PM -0700, Crispin Cowan wrote:
> >> Greg KH wrote:
> >>> On Fri, Jun 15, 2007 at 10:06:23PM +0200, Pavel Machek wrote:
> >>>> Only case where attacker _can't_ be keeping file descriptors is newly
> >>>> created files in recently moved tree. But as you already create files
> >>>> with restrictive permissions, that's okay.
> >>>>
> >>>> Yes, you may get some -EPERM during the tree move, but AA has that
> >>>> problem already, see that "when madly moving trees we sometimes
> >>>> construct path file never ever had".
> >>>>
> >>> Exactly.
> >>>
> >> You are remembering old behavior. The current AppArmor generates only
> >> correct and consistent paths. If a process has an open file descriptor
> >> to such a file, they will retain access to it, as we described here:
> >>
> >>
> >> Under the restorecon-alike proposal, you have a HUGE open race. This
> >> post describes restorecon
> >> running for 30 minutes relabeling a file system. That is so far from
> >> acceptable that it is silly.
> >
> > Ok, so we fix it. Seriously, it shouldn't be that hard. If that's the
> > only problem we have here, it isn't an issue.
> how do you 'fix' the laws of physics?
> the problem is that with a directory that contains lots of files below it
> you have to access all the files metadata to change the labels on it. it can
> take significant amounts of time to walk the entire three and change every
> file.

Agreed, but you can do this in ways that are faster than others :)

> >>> I can't think of a "real world" use of moving directory trees around
> >>> that this would come up in as a problem.
> >> Consider this case: We've been developing a new web site for a month,
> >> and testing it on the server by putting it in a different virtual
> >> domain. We want to go live at some particular instant by doing an mv of
> >> the content into our public HTML directory. We simultaneously want to
> >> take the old web site down and archive it by moving it somewhere else.
> >>
> >> Under the restorecon proposal, the web site would be horribly broken
> >> until restorecon finishes, as various random pages are or are not
> >> accessible to Apache.
> >
> > Usually you don't do that by doing a 'mv' otherwise you are almost
> > guaranteed stale and mixed up content for some period of time, not to
> > mention the issues surrounding paths that might be messed up.
> on the contrary, useing 'mv' is by far the cleanest way to do this.
> mv htdocs htdocs.old;mv htdocs
> this makes two atomic changes to the filesystem, but can generate thousands
> to millions of permission changes as a result.

I agree, and yet, somehow, SELinux today handles this just fine, right?

Let's worry about speed issues later on when a working implementation is
produced, I'm still looking for the logical reason a system like this
can not work properly based on the expected AA interface to users.


greg k-h
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