Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

From: "Serge E. Hallyn" <serge@hallyn.com>
To: Seth Forshee <seth.forshee@canonical.com>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@canonical.com>,
	Richard Weinberger <richard.weinberger@gmail.com>,
	Austin S Hemmelgarn <ahferroin7@gmail.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	linux-bcache@vger.kernel.org, dm-devel@redhat.com,
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	fuse-devel@lists.sourceforge.net,
	linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov
Subject: Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns
Date: Fri, 4 Dec 2015 13:42:54 -0600	[thread overview]
Message-ID: <20151204194254.GG3624@mail.hallyn.com> (raw)
In-Reply-To: <20151204174605.GC147214@ubuntu-hedt>

Quoting Seth Forshee (seth.forshee@canonical.com):
> On Fri, Dec 04, 2015 at 11:27:38AM -0600, Serge E. Hallyn wrote:
> > On Wed, Dec 02, 2015 at 09:40:09AM -0600, Seth Forshee wrote:
> > > Add checks to inode_change_ok to verify that uid and gid changes
> > > will map into the superblock's user namespace. If they do not
> > > fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.
> > > 
> > > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> > 
> > Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> > 
> > ...  although i could see root on the host being upset that it can't
> > assign a uid not valid in the mounter's ns.  But it does seem safer.
> 
> That change wouldn't be representable in the backing store though, and
> that could lead to unexpected behaviour. It's better to tell root that
> we can't make the requested change, in my opinion.

Makes sense.  Thanks.