linux-kernel - Re: [PATCH v4 10/15] exec: Use secureexec for setting dumpability

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Date:   Tue, 1 Aug 2017 10:48:17 +1000 (AEST)
From:   James Morris <jmorris@...ei.org>
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 v4 10/15] exec: Use secureexec for setting dumpability

On Mon, 31 Jul 2017, Kees Cook wrote:

> The examination of "current" to decide dumpability is wrong. This was a
> check of and euid/uid (or egid/gid) mismatch in the existing process,
> not the newly created one. This appears to stretch back into even the
> "history.git" tree. Luckily, dumpability is later set in commit_creds().
> In earlier kernel versions before creds existed, similar checks also
> existed late in the exec flow, covering up the mistake as far back as I
> could find.
> 
> Note that because the commit_creds() check examines differences of euid,
> uid, egid, gid, and capabilities between the old and new creds, it would
> look like the setup_new_exec() dumpability test could be entirely removed.
> However, the secureexec test may cover a different set of tests (specific
> to the LSMs) than what commit_creds() checks for. So, fix this test to
> use secureexec (the removed euid tests are redundant to the commoncap
> secureexec checks now).
> 
> Cc: David Howells <dhowells@...hat.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Acked-by: Serge Hallyn <serge@...lyn.com>
> ---
>  fs/exec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

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


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