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Date:   Wed, 13 Nov 2019 18:47:57 +1100
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>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        David Drysdale <drysdale@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Tycho Andersen <tycho@tycho.ws>,
        Chanho Min <chanho.min@lge.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
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Subject: Re: [PATCH v15 4/9] namei: LOOKUP_BENEATH: O_BENEATH-like scoped
 resolution
Message-ID: <20191113074757.5b4u5vlyx2u6pbn6@yavin.dot.cyphar.com>
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On 2019-11-13, Al Viro <viro@zeniv.linux.org.uk> wrote:
> Minor nit here - I'd split "move the conditional call of set_root()
> into nd_jump_root()" into a separate patch before that one.  Makes
> for fewer distractions in this one.  I'd probably fold "and be
> ready for errors other than -ECHILD" into the same preliminary
> patch.

Will do.

> > +			/* Not currently safe for scoped-lookups. */
> > +			if (unlikely(nd->flags & LOOKUP_IS_SCOPED))
> > +				return ERR_PTR(-EXDEV);
>=20
> Also a candidate for doing in nd_jump_link()...
>=20
> > @@ -1373,8 +1403,11 @@ static int follow_dotdot_rcu(struct nameidata *n=
d)
> >  	struct inode *inode =3D nd->inode;
> > =20
> >  	while (1) {
> > -		if (path_equal(&nd->path, &nd->root))
> > +		if (path_equal(&nd->path, &nd->root)) {
> > +			if (unlikely(nd->flags & LOOKUP_BENEATH))
> > +				return -EXDEV;
>=20
> Umm...  Are you sure it's not -ECHILD?

It wouldn't hurt to be -ECHILD -- though it's not clear to me how likely
a success would be in REF-walk if the parent components didn't already
trigger an unlazy_walk() in RCU-walk.

I guess that also means LOOKUP_NO_XDEV should trigger -ECHILD in
follow_dotdot_rcu()?

--=20
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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