linux-kernel - Re: [PATCH v4 2/5] fuse: Support fuse filesystems outside of init_user

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

Message-ID: <20141015150512.GA22951@ubuntu-mba51>
Date:	Wed, 15 Oct 2014 17:05:12 +0200
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge H. Hallyn" <serge.hallyn@...ntu.com>
Subject: Re: [PATCH v4 2/5] fuse: Support fuse filesystems outside of
 init_user_ns

On Wed, Oct 15, 2014 at 07:49:39AM -0700, Andy Lutomirski wrote:
> On 10/14/2014 07:25 AM, Seth Forshee wrote:
> > Update fuse to translate uids and gids to/from the user namspace
> > of the process servicing requests on /dev/fuse. Any ids which do
> > not map into the namespace will result in errors. inodes will
> > also be marked bad when unmappable ids are received from
> > userspace.
> > 
> > Due to security concerns the namespace used should be fixed,
> > otherwise a user might be able to gain elevated privileges or
> > influence processes that the user would otherwise be unable to
> > manipulate. Thus the namespace of the mounting process is used
> > for all translations, and this namespace is required to be the
> > same as the one in use when /dev/fuse was opened.
> > 
> 
> I'm not sure that this is necessary if my nosuid patch goes in, but I
> also don't think it makes any sense to hold this up while we find a
> perfect solution.
> 
> Is there a decent way to extend this to different translation schemes in
> the future (e.g. a flag at fs setup that could be used)?

I think it would be possible to relax the translation scheme
restrictions in the future, certainly that's easier than tightening down
a looser restriction. I still favor picking one namespace to use for
translation (surely that's how it would work with other filesystems
anyway) rather than using the current namespace during /dev/fuse I/O. I
did an implementation using the latter technique, and it's far more
complex with no benefits that I can see.

Thanks,
Seth
--
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/