Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there

[Linus Torvalds <torvalds@linux-foundation.org>]

On Wed, Apr 29, 2020 at 2:57 PM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> I've never had any reason to use FDPIC, and I don't have any binaries
> that would use it.  Nicolas Pitre added ARM support, so I guess he
> would be the one to talk to about it.  (Added Nicolas.)

While we're at it, is there anybody who knows binfmt_flat?

It might be Nicolas too.

binfmt_flat doesn't do core-dumping, but it has some other oddities.
In particular, I'd like to bring sanity to the installation of the new
creds, and all the _normal_ binfmt cases do it largely close together
with setup_new_exec().

binfmt_flat is doing odd things. It's doing this:

        /* Flush all traces of the currently running executable */
        if (id == 0) {
                ret = flush_old_exec(bprm);
                if (ret)
                        goto err;

                /* OK, This is the point of no return */
                set_personality(PER_LINUX_32BIT);
                setup_new_exec(bprm);
        }

in load_flat_file() - which is also used to loading _libraries_. Where
it makes no sense at all.

It does the

        install_exec_creds(bprm);

in load_flat_binary() (which makes more sense: that is only for actual
binary loading, no library case).

I would _like_ for every binfmt loader to do

        /* Flush all traces of the currently running executable */
        retval = flush_old_exec(bprm);
        if (retval)
                return retval;

   .. possibly set up personalities here ..

        setup_new_exec(bprm);
        install_exec_creds(bprm);

all together, and at least merge 'setup_new_exec()' with 'install_exec_creds()'.

And I think all the binfmt handlers would be ok with that, but the
flat one in particular is really oddly set up.

*Particularly* with that flush_old_exec/setup_new_exec() being done by
the same routine that is also loading libraries (and called from
'calc_reloc()' from binary loading too).

Adding Greg Ungerer for m68knommu. Can somebody sort out why that
flush_old_exec/setup_new_exec() isn't in load_flat_binary() like
install_exec_creds() is?

Most of that file goes back to pre-git days. And most of the commits
since are not so much about binfmt_flat, as they are about cleanups or
changes elsewhere where binfmt_flat was just a victim.

               Linus