linux-kernel - Re: [PATCH v2 2/8] exec: Move security_bprm

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Message-ID: <CAGXu5jLw6SsXM66x7ZHdj+Pb8Aepq7rHn1saNHRhq-wqk8p=4g@mail.gmail.com>
Date:   Mon, 10 Jul 2017 09:06:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Serge Hallyn <serge@...lyn.com>,
        John Johansen <john.johansen@...onical.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Michal Hocko <mhocko@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Hugh Dickins <hughd@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...hat.com>,
        James Morris <james.l.morris@...cle.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Ingo Molnar <mingo@...nel.org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Paul Moore <paul@...l-moore.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Mickaël Salaün <mic@...ikod.net>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        SE Linux <selinux@...ho.nsa.gov>
Subject: Re: [PATCH v2 2/8] exec: Move security_bprm_secureexec() earlier

On Mon, Jul 10, 2017 at 1:57 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> There are several places where exec needs to know if a privilege-gain has
>> happened. These should be using the results of security_bprm_secureexec()
>> but it is getting (needlessly) called very late.
>
> It is hard to tell at a glance but I believe this introduces a
> regression.
>
> cap_bprm_set_creds is currently called before cap_bprm_secureexec and
> it has a number of cases such as no_new_privs and ptrace that can result
> in some of the precomputed credential changes not happening.
>
> Without accounting for that I believe your cap_bprm_securexec now
> returns a postive value too early.

It's still before cap_bprm_secureexec. cap_brpm_set_creds() is in
prepare_binprm(), which is well before exec_binprm() and it's eventual
call to setup_new_exec().

-Kees

-- 
Kees Cook
Pixel Security