linux-kernel - Re: [PATCH 05/24] devtmpfs: open code ksys_chdir and ksys

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Message-ID: <20200721182607.GA14450@lst.de>
Date:   Tue, 21 Jul 2020 20:26:07 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-raid@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 05/24] devtmpfs: open code ksys_chdir and ksys_chroot

On Tue, Jul 21, 2020 at 06:16:27PM +0100, Al Viro wrote:
> 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@....de> 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.

Yep.  Only saving grace is that the error just doesn't happen during
early init.