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Date:   Thu, 14 Nov 2019 15:57:44 +1100
From:   Aleksa Sarai <cyphar@cyphar.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
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Subject: Re: [PATCH v15 4/9] namei: LOOKUP_BENEATH: O_BENEATH-like scoped
 resolution
Message-ID: <20191114045744.d3e7mp3zrupfe2wr@yavin.dot.cyphar.com>
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On 2019-11-13, Aleksa Sarai <cyphar@cyphar.com> wrote:
> 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.
>=20
> Will do.
>=20
> > > +			/* 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 =
*nd)
> > >  	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?
>=20
> 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.
>=20
> I guess that also means LOOKUP_NO_XDEV should trigger -ECHILD in
> follow_dotdot_rcu()?

Scratch the last question -- AFAICS we don't need to do that for
LOOKUP_NO_XDEV because we check against mount_lock so it's very unlikely
that -ECHILD will have any benefit.

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

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