linux-kernel - Re: [PATCH v3 00/15] exec: Use sane stack rlimit under secureexec

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Date:   Tue, 18 Jul 2017 22:22:05 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        John Johansen <john.johansen@...onical.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        James Morris <james.l.morris@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/15] exec: Use sane stack rlimit under secureexec

On Tue, Jul 18, 2017 at 03:25:21PM -0700, Kees Cook wrote:
> This series has grown... :P
> 
> As discussed with Linus and Andy, we need to reset the stack rlimit
> before we do memory layouts when execing a privilege-gaining (e.g.
> setuid) program. To do this, we need to know the results of the
> bprm_secureexec hook before memory layouts. As it turns out, this
> can be made _mostly_ trivial by collapsing bprm_secureexec into
> bprm_set_creds.
> 
> The LSMs using bprm_secureexec nearly always save state between
> bprm_set_creds and bprm_secureexec. In the face of multiple calls to
> bprm_set_creds (via prepare_binprm() calls from binfmt_script, etc),
> all LSMs except commoncap only pay attention to the first call, so
> that aligns well with collapsing bprm_secureexec into bprm_set_creds.
> The commoncaps, though, needs to check the _last_ bprm_set_creds, so
> this series just swaps one bprm flag for another (cap_effective is no
> longer needed to save state between bprm_set_creds and bprm_secureexec,
> but we do need to keep a separate state, so we add the cap_elevated flag).
> 
> Once secureexec is available to setup_new_exec() before the memory
> layout, we can add an rlimit sanity-check for setuid execs. (With no
> need to clean up since we're past the point of no return.)
> 
> Along the way, this fixes comments, renames a variable, and consolidates
> dumpability and pdeath_signal clearing, which includes some commit log
> archeology to examine the subtle differences between what we had and
> what we need.
> 
> I'd appreciate some extra eyes on this to make sure this isn't broken
> in some special way. Looking at the diffstat, even after all my long
> comments, this is a net reduction in lines. :)
> 
> Given this crosses a bunch of areas, I think this is likely best to
> go via the -mm tree, which is where nearly all of my prior exec work
> has lived too.
> 
> Thanks!
> 
> -Kees
> ----------------------------------------------------------------
> Kees Cook (15):
>       binfmt: Introduce secureexec flag
>       exec: Rename bprm->cred_prepared to called_set_creds
>       apparmor: Refactor to remove bprm_secureexec hook
>       selinux: Refactor to remove bprm_secureexec hook
>       smack: Refactor to remove bprm_secureexec hook
>       commoncap: Refactor to remove bprm_secureexec hook
>       commoncap: Move cap_elevated calculation into bprm_set_creds
>       LSM: drop bprm_secureexec hook
>       exec: Correct comments about "point of no return"
>       exec: Use secureexec for setting dumpability
>       exec: Use secureexec for clearing pdeath_signal
>       smack: Remove redundant pdeath_signal clearing
>       exec: Consolidate dumpability logic
>       exec: Use sane stack rlimit under secureexec
>       exec: Consolidate pdeath_signal clearing

Thanks, the set looks good to me,

Acked-by: Serge Hallyn <serge@...lyn.com>

Have you had a chance to run the ltp caps tests against this?

-serge