From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Morris Subject: Re: [PATCH v3 4/7] fs: Treat foreign mounts as nosuid Date: Wed, 18 Nov 2015 11:00:53 +1100 (AEDT) Message-ID: References: <1447778351-118699-1-git-send-email-seth.forshee@canonical.com> <1447778351-118699-5-git-send-email-seth.forshee@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <1447778351-118699-5-git-send-email-seth.forshee@canonical.com> Sender: linux-kernel-owner@vger.kernel.org To: Seth Forshee Cc: "Eric W. Biederman" , Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" , Paul Moore , Stephen Smalley , Eric Paris , Andy Lutomirski , linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov List-Id: linux-raid.ids On Tue, 17 Nov 2015, Seth Forshee wrote: > From: Andy Lutomirski > > If a process gets access to a mount from a different user > namespace, that process should not be able to take advantage of > setuid files or selinux entrypoints from that filesystem. Prevent > this by treating mounts from other mount namespaces and those not > owned by current_user_ns() or an ancestor as nosuid. > > This will make it safer to allow more complex filesystems to be > mounted in non-root user namespaces. > > This does not remove the need for MNT_LOCK_NOSUID. The setuid, > setgid, and file capability bits can no longer be abused if code in > a user namespace were to clear nosuid on an untrusted filesystem, > but this patch, by itself, is insufficient to protect the system > from abuse of files that, when execed, would increase MAC privilege. > > As a more concrete explanation, any task that can manipulate a > vfsmount associated with a given user namespace already has > capabilities in that namespace and all of its descendents. If they > can cause a malicious setuid, setgid, or file-caps executable to > appear in that mount, then that executable will only allow them to > elevate privileges in exactly the set of namespaces in which they > are already privileges. > > On the other hand, if they can cause a malicious executable to > appear with a dangerous MAC label, running it could change the > caller's security context in a way that should not have been > possible, even inside the namespace in which the task is confined. > > As a hardening measure, this would have made CVE-2014-5207 much > more difficult to exploit. > > Signed-off-by: Andy Lutomirski > Signed-off-by: Seth Forshee Acked-by: James Morris -- James Morris