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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 27 Oct 2019 08:05:11 -0400
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Subject: Re: [PATCH RESEND v14 2/6] namei: LOOKUP_IN_ROOT: chroot-like path
 resolution
To: Aleksa Sarai <cyphar@cyphar.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Sat, Oct 26, 2019 at 2:58 PM Aleksa Sarai <cyphar@cyphar.com> wrote:
>
> +       /* LOOKUP_IN_ROOT treats absolute paths as being relative-to-dirfd. */
> +       if (flags & LOOKUP_IN_ROOT)
> +               while (*s == '/')
> +                       s++;
> +
>         /* Figure out the starting path and root (if needed). */
>         if (*s == '/') {
>                 error = nd_jump_root(nd);

So I'm still hung up on this.

I guess I can't help it, but I look at the above, and it makes me go
"whoever wrote those tests wasn't thinking".

It just annoys me how it tests for '/' completely unnecessarily.

If LOOKUP_IN_ROOT is true, we know the subsequent test for '/' is not
going to match, because we just removed it. So I look at that code and
go "that code is doing stupid things".

That's why I suggested moving the LOOKUP_IN_ROOT check inside the '/' test.

Alternatively, just make the logic be

        if (flags & LOOKUP_IN_ROOT) {
               .. remove '/'s ...
        } else if (*s == '/') {
                .. handl;e root ..

and remove the next "else" clause

    Linus