From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 05/24] devtmpfs: open code ksys_chdir and ksys_chroot
Date: Tue, 21 Jul 2020 20:26:07 +0200
Message-ID: <20200721182607.GA14450@lst.de>
References: <20200721162818.197315-1-hch@lst.de> <20200721162818.197315-6-hch@lst.de> <CAHk-=wi0GQqAq6VSY=O2iWnPuuS54TkyRBH5B9Ca0Kg5A9d2aA@mail.gmail.com> <20200721171627.GZ2786714@ZenIV.linux.org.uk>
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To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Christoph Hellwig <hch@lst.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-raid@vger.kernel.org, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>
List-Id: linux-raid.ids

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@lst.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.