linux-kernel - Re: [PATCH v3 10/15] exec: Use secureexec for setting dumpability

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Date:   Tue, 25 Jul 2017 20:59:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.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-fsdevel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 10/15] exec: Use secureexec for setting dumpability

On Tue, Jul 18, 2017 at 3:25 PM, Kees Cook <keescook@...omium.org> 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>

David (or anyone else), how does this (and the following undiscussed
patches) look? I only have a few unreviewed patches in this series,
and I'd like to get some more eyes on it.

Thanks!

-Kees

> ---
>  fs/exec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index f9480d3e0b82..5241c8f25f5d 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1353,7 +1353,7 @@ void setup_new_exec(struct linux_binprm * bprm)
>
>         current->sas_ss_sp = current->sas_ss_size = 0;
>
> -       if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
> +       if (!bprm->secureexec)
>                 set_dumpable(current->mm, SUID_DUMP_USER);
>         else
>                 set_dumpable(current->mm, suid_dumpable);
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security