On Feb 4, 2015 7:56 AM, "Serge E. Hallyn" <[email protected]> wrote: > > Quoting Christoph Lameter ([email protected]): > > 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 [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
