ipc: Restrict mounting the mqueue filesystem

commit a636b702ed1805e988ad3d8ff8b52c060f8b341c upstream.

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.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 6ebfbf52712de6f29e6fd4ada9ac4aac6a8d0b80..f3f40dc2aa86ceef8bcb895de9cad141e14835a4 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);
 }