Re: [PATCH v15 5/9] namei: LOOKUP_IN_ROOT: chroot-like scoped resolution

[Aleksa Sarai <cyphar@xxxxxxxxxx>]

On 2019-11-13, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Nov 05, 2019 at 08:05:49PM +1100, Aleksa Sarai wrote:
> 
> > @@ -2277,12 +2277,20 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> >  
> >  	nd->m_seq = read_seqbegin(&mount_lock);
> >  
> > -	/* Figure out the starting path and root (if needed). */
> > -	if (*s == '/') {
> > +	/* Absolute pathname -- fetch the root. */
> > +	if (flags & LOOKUP_IN_ROOT) {
> > +		/* With LOOKUP_IN_ROOT, act as a relative path. */
> > +		while (*s == '/')
> > +			s++;
> 
> 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@xxxxxxxxxxxxxxxxxx/

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

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