Re: [PATCH 05/24] devtmpfs: open code ksys_chdir and ksys_chroot

[Al Viro]

On Tue, Jul 21, 2020 at 09:49:17AM -0700, Linus Torvalds wrote:
> On Tue, Jul 21, 2020 at 9:28 AM Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > +
> > +       /* traverse into overmounted root and then chroot to it */
> > +       if (!kern_path("/..", LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path) &&
> > +           !inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR) &&
> > +           ns_capable(current_user_ns(), CAP_SYS_CHROOT) &&
> > +           !security_path_chroot(&path)) {
> > +               set_fs_pwd(current->fs, &path);
> > +               set_fs_root(current->fs, &path);
> > +       }
> > +       path_put(&path);
> 
> This looks wrong.

It is wrong.  kern_path() leaves *path unmodified in case of error, and
that struct path is uninitialized here.