[PATCH 0/2] exec: Use sane stack rlimit for setuid exec

[Kees Cook]

As discussed with Linus and Andy, we need to reset the stack rlimit
before we do memory layouts when execing a privilege-gaining (e.g.
setuid) program. This moves security_bprm_secureexec() earlier (with
required changes), and then lowers the stack limit when appropriate.

As a side-effect, dumpability is expanded to cover capabilities and
other LSM definitions of secureexec, and Smack can drop its special
handler for pdeath_signal clearing.

I'd appreciate some extra eyes on this to make sure this isn't
broken in some special way. I couldn't find anything that _depended_
on security_bprm_secureexec() being called late.

Thanks!

-Kees