Date: Fri, 4 Oct 2013 20:11:13 +0100 From: Djalal Harouni <tixxdz@...ndz.org> To: Andy Lutomirski <luto@...capital.net> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, David Rientjes <rientjes@...gle.com>, LKML <linux-kernel@...r.kernel.org>, Linux FS Devel <linux-fsdevel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Djalal Harouni <tixxdz@...il.com> Subject: Re: [PATCH v2 2/9] procfs: add proc_allow_access() to check if file's opener may access task 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@...ndz.org> 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@...ndz.org> 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? -- Djalal Harouni http://opendz.org
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