ipc: Restrict mounting the mqueue filesystem

Only allow mounting the mqueue filesystem if the caller has CAP_SYS_ADMIN
rights over the ipc namespace.   The principle here is if you create
or have capabilities over it you can mount it, otherwise you get to live
with what other people have mounted.

This information is not particularly sensitive and mqueue essentially
only reports which posix messages queues exist.  Still when creating a
restricted environment for an application to live any extra
information may be of use to someone with sufficient creativity.  The
historical if imperfect way this information has been restricted has
been not to allow mounts and restricting this to ipc namespace
creators maintains the spirit of the historical restriction.

Cc: stable@vger.kernel.org
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index e5c4f609f22c2a902789e710756aa117f40cf5cc..c4ae32ec6c6b09a9cae21c23840a215e185dff71 100644 (file)
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -330,8 +330,16 @@ static struct dentry *mqueue_mount(struct file_system_type *fs_type,
                         int flags, const char *dev_name,
                         void *data)
 {
-       if (!(flags & MS_KERNMOUNT))
-               data = current->nsproxy->ipc_ns;
+       if (!(flags & MS_KERNMOUNT)) {
+               struct ipc_namespace *ns = current->nsproxy->ipc_ns;
+               /* Don't allow mounting unless the caller has CAP_SYS_ADMIN
+                * over the ipc namespace.
+                */
+               if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+                       return ERR_PTR(-EPERM);
+
+               data = ns;
+       }
        return mount_ns(fs_type, flags, data, mqueue_fill_super);
 }