linux-kernel - Re: [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path

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Date:   Fri, 12 Jul 2019 22:12:01 +1000
From:   Aleksa Sarai <cyphar@...har.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     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>,
        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>,
        Christian Brauner <christian@...uner.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Drysdale <drysdale@...gle.com>,
        Chanho Min <chanho.min@....com>,
        Oleg Nesterov <oleg@...hat.com>, Aleksa Sarai <asarai@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        containers@...ts.linux-foundation.org, linux-alpha@...r.kernel.org,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v9 04/10] namei: split out nd->dfd handling to
 dirfd_path_init

On 2019-07-12, Aleksa Sarai <cyphar@...har.com> wrote:
> On 2019-07-12, Al Viro <viro@...iv.linux.org.uk> wrote:
> > On Sun, Jul 07, 2019 at 12:57:31AM +1000, Aleksa Sarai wrote:
> > > Previously, path_init's handling of *at(dfd, ...) was only done once,
> > > but with LOOKUP_BENEATH (and LOOKUP_IN_ROOT) we have to parse the
> > > initial nd->path at different times (before or after absolute path
> > > handling) depending on whether we have been asked to scope resolution
> > > within a root.
> > 
> > >  	if (*s == '/') {
> > > -		set_root(nd);
> > > -		if (likely(!nd_jump_root(nd)))
> > > -			return s;
> > > -		return ERR_PTR(-ECHILD);
> > 
> > > +		if (likely(!nd->root.mnt))
> > > +			set_root(nd);
> > 
> > How can we get there with non-NULL nd->root.mnt, when LOOKUP_ROOT case
> > has been already handled by that point?
> 
> Yup, you're completely right. I will remove the
>   if (!nd->root.mnt)
> in the next version.

Ah sorry, there is a reason for it -- later in the series the
LOOKUP_BENEATH case means that you might end up with a non-NULL
nd->root.mnt. If you want, I can move the addition of the conditional to
later in the series (it was easier to split the patch by-hunk back when
you originally asked me to split out dirfd_path_init()).

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

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