afs: Only allow mounting afs in the intial network namespace

rxrpc sockets only work in the initial network namespace so it isn't
possible to support afs in any other network namespace.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: N"Eric W. Biederman" <ebiederm@xmission.com>

fs/afs/super.c

@@ -24,6 +24,8 @@
 #include <linux/parser.h>
 #include <linux/statfs.h>
 #include <linux/sched.h>
+#include <linux/nsproxy.h>
+#include <net/net_namespace.h>
 #include "internal.h"
 
 #define AFS_FS_MAGIC 0x6B414653 /* 'kAFS' */
@@ -363,6 +365,10 @@ static struct dentry *afs_mount(struct file_system_type *fs_type,
 
 	memset(&params, 0, sizeof(params));
 
+	ret = -EINVAL;
+	if (current->nsproxy->net_ns != &init_net)
+		goto error;
+
 	/* parse the options and device name */
 	if (options) {
 		ret = afs_parse_options(&params, options, &dev_name);