linux-kernel - Re: [PATCH RESEND v14 2/6] namei: LOOKUP_IN

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Message-ID: <20191027154115.ex55njkysey4m6pu@yavin.dot.cyphar.com>
Date:   Mon, 28 Oct 2019 02:41:15 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Tycho Andersen <tycho@...ho.ws>,
        David Drysdale <drysdale@...gle.com>,
        Chanho Min <chanho.min@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Aleksa Sarai <asarai@...e.de>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        alpha <linux-alpha@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        GNU C Library <libc-alpha@...rceware.org>,
        linux-arch <linux-arch@...r.kernel.org>,
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        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
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Subject: Re: [PATCH RESEND v14 2/6] namei: LOOKUP_IN_ROOT: chroot-like path
 resolution

On 2019-10-27, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Sat, Oct 26, 2019 at 2:58 PM Aleksa Sarai <cyphar@...har.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".

Okay, fair enough.

> 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

I've gone with the latter since I think it reads better.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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