Re: [PATCH v2 resend] vfs: new O_NODE open flag

From: Pavel Machek
Date: Fri Nov 06 2009 - 09:17:56 EST

On Thu 2009-11-05 15:27:06, Miklos Szeredi wrote:
> On Thu, 5 Nov 2009, Alan Cox wrote:
> > > - re-opening normally after checking file type (there's a debate
> > > whether this would have security issues, but currently we do allow
> > > re-opening with increased permissions thorugh /proc/*/fd)
> >
> > Which has already been demonstrated to be an (unfixed) security hole.
> No it hasn't :) Jamie theorized that there *might* be a real world
> situation where the application writer didn't anticipate this
> behavior. But as to actual demonstration, we have not seen one yet, I
> think.

See bugtraq, or lkml thread about symlinks with permissions. There's
demo script there.

> And as for reopening O_NODE files with increased permission: that's
> feature people actually expressed interest in, so it's hardly a
> security hole, is it?

Just because people want it does not mean it is not a security hole.

Consider passing /etc/shadow filedesciptor to (legacy) suid root
program. Maybe it now prints /etc/shadow content, because it assumes
that if you have fd you are allowed to read the file?

(cesky, pictures)
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