Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754411Ab3JDTlu (ORCPT ); Fri, 4 Oct 2013 15:41:50 -0400 Received: from numidia.opendz.org ([98.142.220.152]:50822 "EHLO numidia.opendz.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754091Ab3JDTls (ORCPT ); Fri, 4 Oct 2013 15:41:48 -0400 Date: Fri, 4 Oct 2013 20:41:42 +0100 From: Djalal Harouni To: Andy Lutomirski Cc: "Eric W. Biederman" , Kees Cook , Al Viro , Andrew Morton , Linus Torvalds , Ingo Molnar , "Serge E. Hallyn" , Cyrill Gorcunov , David Rientjes , LKML , Linux FS Devel , "kernel-hardening@lists.openwall.com" , Djalal Harouni Subject: Re: [PATCH v2 2/9] procfs: add proc_allow_access() to check if file's opener may access task Message-ID: <20131004194142.GA4524@dztty> References: <20131003201332.GA3500@dztty> <20131004085911.GA2157@dztty> <20131004182353.GA2600@dztty> <20131004191113.GA3916@dztty> <20131004192712.GA4334@dztty> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4289 Lines: 115 On Fri, Oct 04, 2013 at 12:32:09PM -0700, Andy Lutomirski wrote: > On Fri, Oct 4, 2013 at 12:27 PM, Djalal Harouni wrote: > > On Fri, Oct 04, 2013 at 12:16:26PM -0700, Andy Lutomirski wrote: > >> On Fri, Oct 4, 2013 at 12:11 PM, Djalal Harouni wrote: > >> > On Fri, Oct 04, 2013 at 07:34:08PM +0100, Andy Lutomirski wrote: > >> >> On Fri, Oct 4, 2013 at 7:23 PM, Djalal Harouni wrote: > >> >> > On Fri, Oct 04, 2013 at 04:40:01PM +0100, Andy Lutomirski wrote: > >> >> >> On Fri, Oct 4, 2013 at 9:59 AM, Djalal Harouni wrote: > >> >> >> > On Thu, Oct 03, 2013 at 02:09:55PM -0700, Andy Lutomirski wrote: > >> > [...] > >> >> Sorry, I described the obviously broken scenario incorrectly. Your > >> >> patch breaks (in the absence of things like selinux) if a exec > >> >> something setuid root. > >> >> > >> >> [...] > >> >> > >> >> > > >> >> > I did the check in the proc_same_open_cred() function: > >> >> > return (uid_eq(fcred->uid, cred->uid) && > >> >> > gid_eq(fcred->gid, cred->gid) && > >> >> > cap_issubset(cred->cap_permitted, fcred->cap_permitted)); > >> >> > >> >> Which has nothing to do with anything. If that check fails, you're > >> >> just going on to a different, WRONG check/. > >> >> > >> >> > > >> >> > Check if this is the same uid/gid and the capabilities superset! > >> >> > > >> >> > But in the proc_allow_access() the capabilities superset is missing. > >> >> > > >> >> > > >> >> > So to fix it: > >> >> > 1) if proc_same_open_cred() detects that cred have changed between > >> >> > ->open() and ->read() then abort, return zero, the ->read(),write()... > >> >> > >> >> IMO yuck. > >> >> > >> >> > > >> >> > > >> >> > 2) Improve the proc_allow_access() check by: > >> >> > if this is the same user namespace then check uid/gid of f_cred on > >> >> > target cred task, and the capabilities superset: > >> >> > cap_issubset(tcred->cap_permitted, fcred->cap_permitted)); > >> >> > > >> >> > If it fails let security_capable() or file_ns_capable() do its magic. > >> >> > > >> >> > >> >> NAK. You need to actually call the LSM. What if the reason to fail > >> >> the request isn't that the writer gained capabilities -- what if the > >> >> writer's selinux label changed? > >> > Sorry I can't follow you here! Can you be more explicit please? > >> > > >> > For me we are already doing this during ptrace_may_access() on each > >> > syscall, which will call LSM to inspect the privileges on each ->open(), > >> > ->write()... So LSM hooks are already called. If you want to have more > >> > LSM hooks, then perhaps that's another problem? > >> > >> Can you show me where, in your code, LSMs are asked whether the > >> process calling read() is permitted to ptrace the process that the > >> proc file points at? > > Yes. > > [PATCH v2 9/9] procfs: improve permission checks on /proc/*/syscall > > > > ->read() > > ->syscall_read() > > ->lock_trace() > > ->ptrace_may_access() > > ->__ptrace_may_access() > > ->security_ptrace_access_check() > > ->yama_ptrace_access_check() > > ->security_ops->ptrace_access_check() > > > > > > And also for patch: > > [PATCH v2 8/9] procfs: improve permission checks on /proc/*/stack > > > > And during ->open() and ->read() > > > > > > So sorry Andy, I don't follow what you are describing. > > And what parameters are you passing to security_ptrace_access_check? > It's supposed to be f_cred, right? Because you want to make sure > that, if the opener had some low-privilege label, the target has > execed and gotten a more secure label, and the reader has a > high-privilege label, that the opener's label is checked against the > target's new label. The current's cred each time. Is there some mechanism to check what you describe? > --Andy > > > > >> --Andy > > > > -- > > Djalal Harouni > > http://opendz.org > > > > -- > Andy Lutomirski > AMA Capital Management, LLC -- Djalal Harouni http://opendz.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/