[PATCH v2 1/8] exec: Teach prepare_exec_creds how exec treats uids & gids

[Kees Cook]

On Mon, May 18, 2020 at 07:29:41PM -0500, Eric W. Biederman wrote:
> 
> It is almost possible to use the result of prepare_exec_creds with no
> modifications during exec.  Update prepare_exec_creds to initialize
> the suid and the fsuid to the euid, and the sgid and the fsgid to the
> egid.  This is all that is needed to handle the common case of exec
> when nothing special like a setuid exec is happening.
> 
> That this preserves the existing behavior of exec can be verified
> by examing bprm_fill_uid and cap_bprm_set_creds.

Yup, agreed.

> This change makes it clear that the later parts of exec that
> update bprm->cred are just need to handle special cases such
> as setuid exec and change of domains.

One question, though: why add this, since the repeat calling of the caps
LSM hook will do this? Is there a call ordering change here, or is this
just to make the new LSM hook more robust?

Regardless, this looks correct, if perhaps redundant. :)

Reviewed-by: Kees Cook <keescook at chromium.org>

-- 
Kees Cook