linux-kernel - Re: [PATCH v3 06/15] commoncap: Refactor to remove bprm

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Date:   Wed, 19 Jul 2017 19:26:28 +1000 (AEST)
From:   James Morris <jmorris@...ei.org>
To:     Kees Cook <keescook@...omium.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Serge Hallyn <serge@...lyn.com>,
        Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        John Johansen <john.johansen@...onical.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>,
        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 06/15] commoncap: Refactor to remove bprm_secureexec
 hook

On Tue, 18 Jul 2017, Kees Cook wrote:

> The commoncap implementation of the bprm_secureexec hook is the only LSM
> that depends on the final call to its bprm_set_creds hook (since it may
> be called for multiple files, it ignores bprm->called_set_creds). As a
> result, it cannot safely _clear_ bprm->secureexec since other LSMs may
> have set it.  Instead, remove the bprm_secureexec hook by introducing a
> new flag to bprm specific to commoncap: cap_elevated. This is similar to
> cap_effective, but that is used for a specific subset of elevated
> privileges, and exists solely to track state from bprm_set_creds to
> bprm_secureexec. As such, it will be removed in the next patch.
> 
> Here, set the new bprm->cap_elevated flag when setuid/setgid has happened
> from bprm_fill_uid() or fscapabilities have been prepared. This temporarily
> moves the bprm_secureexec hook to a static inline. The helper will be
> removed in the next patch; this makes the step easier to review and bisect,
> since this does not introduce any changes to inputs nor outputs to the
> "elevated privileges" calculation.
> 
> The new flag is merged with the bprm->secureexec flag in setup_new_exec()
> since this marks the end of any further prepare_binprm() calls.
> 
> Cc: Serge Hallyn <serge@...lyn.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>


Acked-by: James Morris <james.l.morris@...cle.com>


-- 
James Morris
<jmorris@...ei.org>