linux-kernel - Re: [PATCH v3 01/15] binfmt: Introduce secureexec flag

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Date:   Tue, 18 Jul 2017 18:01:22 -0700
From:   Andy Lutomirski <luto@...nel.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 FS Devel <linux-fsdevel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 01/15] binfmt: Introduce secureexec flag

On Tue, Jul 18, 2017 at 3:25 PM, Kees Cook <keescook@...omium.org> wrote:
> To begin this refactoring, this adds the secureexec flag to the bprm
> struct, which will eventually be used in place of the LSM hook.

I'm very confused.  See below.  Maybe a later patch will unconfuse me.

>
> Cc: David Howells <dhowells@...hat.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  fs/binfmt_elf.c         | 3 ++-
>  fs/binfmt_elf_fdpic.c   | 3 ++-
>  include/linux/binfmts.h | 8 +++++++-
>  3 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 5075fd5c62c8..991e4de3515f 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -254,7 +254,8 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
>         NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));
>         NEW_AUX_ENT(AT_GID, from_kgid_munged(cred->user_ns, cred->gid));
>         NEW_AUX_ENT(AT_EGID, from_kgid_munged(cred->user_ns, cred->egid));
> -       NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
> +       bprm->secureexec |= security_bprm_secureexec(bprm);
> +       NEW_AUX_ENT(AT_SECURE, bprm->secureexec);

This is ->load_binary ...

> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
> index 05488da3aee9..9508b5f83c7e 100644
> --- a/include/linux/binfmts.h
> +++ b/include/linux/binfmts.h
> @@ -27,9 +27,15 @@ struct linux_binprm {
>         unsigned int
>                 cred_prepared:1,/* true if creds already prepared (multiple
>                                  * preps happen for interpreters) */
> -               cap_effective:1;/* true if has elevated effective capabilities,
> +               cap_effective:1,/* true if has elevated effective capabilities,
>                                  * false if not; except for init which inherits
>                                  * its parent's caps anyway */
> +               /*
> +                * Set by bprm_set_creds hook to indicate a privilege-gaining
> +                * exec has happened. Used to sanitize execution environment
> +                * and to set AT_SECURE auxv for glibc.
> +                */

... which is not bprm_set_creds().

What am I missing here?