On Fri, Oct 4, 2013 at 12:27 PM, Djalal Harouni <tixxdz@xxxxxxxxxx> 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 <tixxdz@xxxxxxxxxx> 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 <tixxdz@xxxxxxxxxx> 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 <tixxdz@xxxxxxxxxx> 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. --Andy > >> --Andy > > -- > Djalal Harouni > http://opendz.org -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
