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Date: Sat, 11 Feb 2012 14:21:06 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Subject: Re: procfs: infoleaks and DAC permissions
On Sat, Feb 11, 2012 at 13:20 +0400, Solar Designer wrote:
> On Fri, Feb 10, 2012 at 06:36:17PM +0400, Vasiliy Kulikov wrote:
> > On Fri, Feb 10, 2012 at 03:06 +0100, Djalal Harouni wrote:
> > > 2) DAC permissions and suid/guid/privileged programs (userspace):
> > > This is a list of files that are supposed to be protected:
> > > /proc/<pid>/maps
> ...
> > I cannot find any solution of (2) except actually add ptrace check at
> > open() time... Looks like we have to check what specific action glibc
> > does with /proc/$pid/maps and whitelist these idiotic actions. I hope
> > it is not arbitrary reads :-)
>
> I did not look into this closely, but my current understanding is that
> apparently glibc reads the process' own proc files only, and restricting
> their perms to 0400 breaks this if the process changes euid/fsuid during
> its runtime. Right?
Yes, AFAICS, it looks whether a specific memory area is RW. But looking
at "grep -r /proc/self/ glibc-sources/" output I can say /proc/self/maps
is not the only file usage which might be broken by open() restricting.
> How about including a DAC bypass (perhaps limited to certain files only)
> if the calling process' PID matches the PID in the pathname?
You mean s/PID/task_struct/ as PID is not a system global id in case of
pid namespaces.
> This feels
> very dirty, but it might work. I mention this possibility primarily
> such that maybe we can arrive at something cleaner based on this thought.
>
> Oh, here's a slightly cleaner alternative: instead of basing this on a
> PID match, base it on unique exec_id match.
More clean way - leave 0444 POSIX perms, but add a check at open():
if (current != task && !ptrace_may_access(task, PTRACE_MODE_READ))
return -EPERM;
We should not limit processes to POSIX security domains, but to any
defined Linux domains including LSMs. In general, POSIX permissions in
/proc/$PID/* are obscure exactly because of such non-POSIX security models.
> I am referring to those
> from Spender's patch:
>
> > [1] http://grsecurity.net/~spender/dev_patches/distros_should_sponsor_me_for_doing_their_jobs.patch
>
> BTW, I like this approach.
It is very similar to ->self_exec_id, which was used before, but with
really unique ids ;)
--
Vasiliy
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