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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 29 Apr 2020 16:03:29 -0700
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Subject: Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem
 properly in there
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>,
        Greg Ungerer <gerg@linux-m68k.org>
Cc:     Jann Horn <jannh@google.com>, Nicolas Pitre <nico@fluxnic.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Mark Salter <msalter@redhat.com>,
        Aurelien Jacquiot <jacquiot.aurelien@gmail.com>,
        linux-c6x-dev@linux-c6x.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        Linux-sh list <linux-sh@vger.kernel.org>
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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