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Date:   Wed, 13 Nov 2019 13:44:14 +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>,
        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>, Tycho Andersen <tycho@tycho.ws>,
        David Drysdale <drysdale@google.com>,
        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>,
        Christian Brauner <christian@brauner.io>,
        Aleksa Sarai <asarai@suse.de>,
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Subject: Re: [PATCH v15 5/9] namei: LOOKUP_IN_ROOT: chroot-like scoped
 resolution
Message-ID: <20191113024414.wlmvtjstpnkxa36n@yavin.dot.cyphar.com>
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On 2019-11-13, Al Viro <viro@zeniv.linux.org.uk> wrote:
> On Tue, Nov 05, 2019 at 08:05:49PM +1100, Aleksa Sarai wrote:
>=20
> > @@ -2277,12 +2277,20 @@ static const char *path_init(struct nameidata *=
nd, unsigned flags)
> > =20
> >  	nd->m_seq =3D read_seqbegin(&mount_lock);
> > =20
> > -	/* Figure out the starting path and root (if needed). */
> > -	if (*s =3D=3D '/') {
> > +	/* Absolute pathname -- fetch the root. */
> > +	if (flags & LOOKUP_IN_ROOT) {
> > +		/* With LOOKUP_IN_ROOT, act as a relative path. */
> > +		while (*s =3D=3D '/')
> > +			s++;
>=20
> Er...  Why bother skipping slashes?  I mean, not only link_path_walk()
> will skip them just fine, you are actually risking breakage in this:
>                 if (*s && unlikely(!d_can_lookup(dentry))) {
>                         fdput(f);
>                         return ERR_PTR(-ENOTDIR);
>                 }
> which is downstream from there with you patch, AFAICS.

I switched to stripping the slashes at your suggestion a few revisions
ago[1], and had (wrongly) assumed we needed to handle "/" somehow in
path_init(). But you're quite right about link_path_walk() -- and I'd be
more than happy to drop it.

[1]: https://lore.kernel.org/lkml/20190712125552.GL17978@ZenIV.linux.org.uk/

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

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