Re: [SECURITY] /proc/$pid/ leaks contents across setuid exec

[Kees Cook <kees.cook@canonical.com>]

On Tue, Feb 08, 2011 at 02:43:15PM +1100, James Morris wrote:
> On Mon, 7 Feb 2011, Kees Cook wrote:
> > Sure, I know about O_CLOEXEC, but this is about protecting the
> > just-been-execed setuid process from the attacking process that has no
> > reason to set O_CLOEXEC.
> > 
> > Something like this needs to be enforced on the kernel side. I.e. these
> > file in /proc need to have O_CLOEXEC set in a way that cannot be unset.
> > 
> > > Changing the behavior in the core kernel will break userspace.
> > 
> > I don't think /proc/$pid/* needs to stay open across execs, does it? Or at
> > least the non-0444 files should be handled separately.
> 
> Actually, this seems like a more general kind of bug in proc rather than a 
> leaked fd.  Each child task should only see its own /proc/[pid] data.

Right, that's precisely the problem. The unprivileged process can read
the setuid process's /proc files.

-Kees

-- 
Kees Cook
Ubuntu Security Team