AT_EXECPATH aux_info vector contains path of interpreter when directly exec'ing rtld

[Konstantin Belousov]

On Fri, Dec 20, 2019 at 04:26:41PM -0500, Ryan Stone wrote:
> I've noticed that on head, if I directly execute rtld to run an
> executable, AT_EXECPATH contains the path to rtld on head (on
> 12.0-RELEASE it will contain nothing).  This is causing me a problem
> because clang uses AT_EXECPATH to preferentially locate where it's
> installed, which it uses to locate its driver programs.
> 
> The end result is that clang can no longer successfully be executed
> from a process in capability mode, whereas before I could fexecve rtld
> and give it a pre-opened file descriptor to /usr/bin/clang.
> 
> I've put together a quick test program demonstrating the problem:
> 
> https://people.freebsd.org/~rstone/getprogname.c
> 
> On 12.0-RELEASE, directly executing rtld to run this program gives this output:
> $ /libexec/ld-elf.so.1 -- ./progname
> progname: progname
> argv[0]:  ./progname
> elf_aux_info failed: No such file or directory
> 
> On head, I get this instead:
> /libexec/ld-elf.so.1 -- ./progname
> progname: progname
> argv[0]:  ./progname
> AT_EXECPATH: /libexec/ld-elf.so.1

https://reviews.freebsd.org/D22894