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

From: Aleksa Sarai <cyphar@cyphar.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jeff Layton <jlayton@kernel.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Arnd Bergmann <arnd@arndb.de>,
	David Howells <dhowells@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Eric Biederman <ebiederm@xmission.com>,
	Andy Lutomirski <luto@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
	Christian Brauner <christian@brauner.io>,
	Tycho Andersen <tycho@tycho.ws>,
	David Drysdale <drysdale@google.com>,
	Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
	Aleksa Sarai <asarai@suse.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	containers@lists.linux-foundation.org,
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Subject: Re: [PATCH v9 04/10] namei: split out nd->dfd handling to dirfd_path_init
Date: Fri, 12 Jul 2019 22:12:01 +1000	[thread overview]
Message-ID: <20190712121201.ouhwqgeszfq44t33@yavin> (raw)
In-Reply-To: <20190712120743.mka3vl5t4zndc5wj@yavin>

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On 2019-07-12, Aleksa Sarai <cyphar@cyphar.com> wrote:
> On 2019-07-12, Al Viro <viro@zeniv.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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