linux-kernel - Re: [PATCH v2] vfs: add NOFOLLOW flag to umount(2)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <E1Njeua-0000Fd-2b@pomaz-ex.szeredi.hu>
Date:	Mon, 22 Feb 2010 21:29:48 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	hch@...radead.org, miklos@...redi.hu,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	eugene@...hat.com, mtk.manpages@...il.com, 7eggert@....de
Subject: Re: [PATCH v2] vfs: add NOFOLLOW flag to umount(2)

On Sun, 21 Feb 2010, Al Viro wrote:
> On Thu, Feb 11, 2010 at 12:21:00PM -0500, Christoph Hellwig wrote:
> > On Wed, Feb 10, 2010 at 12:15:53PM +0100, Miklos Szeredi wrote:
> > >  - renamed flag to UMOUNT_NOFOLLOW
> > >  - added UMOUNT_UNUSED for feature detection
> > 
> > Umm, why?  MNT_ certainly isn't the best naming for unmount flags,
> > but switching convention after we had a few doesn't make any sense.
> 
> Actually, I've got more interesting question: what's being attempted
> there?  Is that just a "let's protect ourselves against somebody feeding
> us an untrusted symlink"?  I'm not sure if it makes much sense; if we
> are dealing with pathnames on untrusted fs, there's nothing to stop the
> attacker from having /mnt/foo/dir (originally containing a mountpoint
> at /mnt/foo/dir/usr) killed and replaced with a symlink to /, making any
> code that does umount() on such pathnames vulnerable as hell anyway.

It is trivial to check the path up to the mountpoint (chdir + getcwd).
But doing that on the mountpoint will make it busy, so NOFOLLOW is
really needed there.

Thanks,
Miklos
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/