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SubjectRe: [PATCH 2/2] exec: Compute file based creds only once
On Fri, May 29, 2020 at 10:28:41PM -0500, Eric W. Biederman wrote:
> The range-diff winds up being:
> 1: c9258ef4879b ! 1: a7868323c263 exec: Add a per bprm->file version of per_clear
> @@ Commit message
>
> History Tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
> Fixes: 1bb0fa189c6a ("[PATCH] NX: clean up legacy binary support")
> + Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>
> ## fs/exec.c ##
> @@ include/linux/lsm_hooks.h
> * transitions between security domains).
> * The hook must set @bprm->active_secureexec to 1 if AT_SECURE should be set to
> * request libc enable secure mode.
> -+ * The hook must set @bprm->pf_per_clear to the personality flags that
> -+ * should be cleared from current->personality.
> ++ * The hook must add to @bprm->pf_per_clear any personality flags that
> ++ * should be cleared from current->personality.
> * @bprm contains the linux_binprm structure.
> * Return 0 if the hook is successful and permission is granted.
> * @bprm_check_security:
> 2: e6f20c69b96e ! 2: 56305aa9b6fa exec: Compute file based creds only once
> @@ Commit message
> secureity attribute and derive capabilities from the fact the
> user had uid 0 has been added.
>
> + Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>
> ## fs/binfmt_misc.c ##
> @@ include/linux/lsm_hooks.h
> + * between security domains).
> + * The hook must set @bprm->secureexec to 1 if AT_SECURE should be set to
> * request libc enable secure mode.
> -- * The hook must set @bprm->pf_per_clear to the personality flags that
> -+ * The hook must set @bprm->per_clear to the personality flags that
> - * should be cleared from current->personality.
> +- * The hook must add to @bprm->pf_per_clear any personality flags that
> ++ * The hook must add to @bprm->per_clear any personality flags that
> + * should be cleared from current->personality.
> * @bprm contains the linux_binprm structure.
> * Return 0 if the hook is successful and permission is granted.

Awesome; thanks!

> > The cap_ambient_invariant_ok() test is needlessly repeated: it doesn't
> > examine securebits, and nonroot_raised_pE appears to have no
> > side-effects.
> >
> > One of those can be dropped, yes?
>
> That is what it looks like to me.

Okay, cool. I was worried I was missing something in the mess of tiny
helper calls. :)

> I hope that when the dust clears the function can become a
> straightforward implementation of the capability equations.
> We will see.

Yeah, this looks better and better every day! I'm glad you're able to
dig through all of this.

--
Kees Cook

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