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

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

Hi James,

On Tue, Feb 08, 2011 at 11:44:40AM +1100, James Morris wrote:
> On Mon, 7 Feb 2011, Kees Cook wrote:
> 
> > $ ./procleak.py auxv,syscall /usr/bin/passwd
> > running
> > AT_BASE:   0x7f2828bde000
> > AT_RANDOM: 0x7fff80bde7c9
> > Changing password for kees.
> > (current) UNIX password: 0 0x0 0x7fff80bdda90 0x1ff 0x7fff80bdd580 0x7f2828dc57c0 0x7f28287cec1d 0x7fff80bdd088 0x7f28282fe6c0
> > 
> > There needs to be some way to break the connection to these files across
> > the setuid exec, or perform some sort of revalidation of permissions. (Maybe
> > check dumpable?)
> 
> The way to do this is to set O_CLOEXEC.

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.

-Kees

-- 
Kees Cook
Ubuntu Security Team