Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161055AbbBDQ1n (ORCPT ); Wed, 4 Feb 2015 11:27:43 -0500 Received: from mail-lb0-f171.google.com ([209.85.217.171]:34768 "EHLO mail-lb0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965761AbbBDQ1k (ORCPT ); Wed, 4 Feb 2015 11:27:40 -0500 MIME-Version: 1.0 In-Reply-To: <20150204155617.GE16726@mail.hallyn.com> References: <20150202171257.GD24351@ubuntumail> <20150203155544.GE2923@mail.hallyn.com> <20150203172653.GB4748@mail.hallyn.com> <20150204155617.GE16726@mail.hallyn.com> From: Andy Lutomirski Date: Wed, 4 Feb 2015 08:27:19 -0800 Message-ID: Subject: Re: [capabilities] Allow normal inheritance for a configurable set of capabilities To: "Serge E. Hallyn" Cc: "linux-kernel@vger.kernel.org" , Andrew Morton , Aaron Jones , LSM List , "Ted Ts'o" , Serge Hallyn , "Andrew G. Morgan" , Christoph Lameter , Serge Hallyn , Jonathan Corbet Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3190 Lines: 73 On Feb 4, 2015 7:56 AM, "Serge E. Hallyn" wrote: > > Quoting Christoph Lameter (cl@linux.com): > > On Wed, 4 Feb 2015, Andrew G. Morgan wrote: > > > > > I'm not generally in favor of this. Mostly because this seems to be a > > > mini-root kind of inheritance that propagates privilege to binaries > > > that aren't prepared for privilege. I don't really buy the mmap code > > > concern because the model as it stands says that you trust the binary > > > (and all of the various ways it was programmed to execute code) with > > > specific privileges. If the binary mmap's some code (PAM modules come > > > to mind) then that is part of what it was programmed to/allowed to do. > > > > > > That being said, if you really really want this kind of thing, then > > > make it a single secure bit (with another lock on/off bit) which, when > > > set, makes: fI default to X. > > > > > > pP' = (X & fP) | (pI & fI) > > > > > > That way the per-process bounding set still works as advertised and > > > you don't need to worry about the existing semantics being violated. > > > > Ok but then also fI needs to be set to X so that the binary f invokes > > can also inherit. So if we copy the inheritable flags to fI then we > > wont be needing the bounding set anymore. > > > > The changes to brpm_caps_from_vfs_cap would then > > be only the following? (substitute capable(CAP_INHERIT_BY_DEFAULT through > > any other means like PRCTL if wanted). > > > > > > Index: linux/security/commoncap.c > > =================================================================== > > --- linux.orig/security/commoncap.c 2015-02-04 09:44:25.000000000 -0600 > > +++ linux/security/commoncap.c 2015-02-04 09:45:59.381572756 -0600 > > @@ -350,6 +350,9 @@ static inline int bprm_caps_from_vfs_cap > > __u32 permitted = caps->permitted.cap[i]; > > __u32 inheritable = caps->inheritable.cap[i]; > > > > + if (capable(CAP_INHERIT_BY_DEFAULT) > > + new->cap_inheritable.cap[i] = inheritable; > > + > > /* > > * pP' = (X & fP) | (pI & fI) > > */ > > Not quite - I think more like > > if (secure(SECURE_AMBIENT_PRIVS)) > new->cap_inheritable.cap[i] = inheritable; I *still* think this should be inheritable & permitted. > > Then ns_capable(CAP_INHERIT_BY_DEFAULT), or perhaps rather > ns_capable(CAP_SETPCAP), would be required in order to set > SECURE_AMBIENT_PRIVS, which is off by default. Can we make this depend on no_new_privs instead of a new cap? I don't want to see people leaking this securebit into the environment for reasons they think are good a la CVE-2014-3215. I sincerely doubt that running, say, sendmail or exim with this bit set and no_new_privs off is a good idea. Hmm. On an unrelated note, we should consider allowing no_new_privs to be cleared in conjunction with unsharing userns. --Andy -- 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/