[PATCH v2 06/10] utsns: Add a limit on the number of uts namespaces

@@ -25,6 +25,7 @@ struct uid_gid_map {	/* 64 bytes -- 1 cache line */
 enum ucounts {
 	UCOUNT_USER_NAMESPACES,
 	UCOUNT_PID_NAMESPACES,
+	UCOUNT_UTS_NAMESPACES,
 	UCOUNT_COUNTS,
 };
 

@@ -78,6 +78,7 @@ static int count_max = COUNT_MAX;
 static struct ctl_table userns_table[] = {
 	UCOUNT_ENTRY("max_user_namespaces"),
 	UCOUNT_ENTRY("max_pid_namespaces"),
+	UCOUNT_ENTRY("max_uts_namespaces"),
 	{ }
 };
 #endif /* CONFIG_SYSCTL */

@@ -17,6 +17,16 @@
 #include <linux/user_namespace.h>
 #include <linux/proc_ns.h>
 
+static bool inc_uts_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, UCOUNT_UTS_NAMESPACES);
+}
+
+static void dec_uts_namespaces(struct user_namespace *ns)
+{
+	dec_ucount(ns, UCOUNT_UTS_NAMESPACES);
+}
+
 static struct uts_namespace *create_uts_ns(void)
 {
 	struct uts_namespace *uts_ns;

@@ -38,15 +48,18 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 	struct uts_namespace *ns;
 	int err;
 
+	err = -ENFILE;
+	if (!inc_uts_namespaces(user_ns))
+		goto fail;
+
+	err = -ENOMEM;
 	ns = create_uts_ns();
 	if (!ns)
-		return ERR_PTR(-ENOMEM);
+		goto fail_dec;
 
 	err = ns_alloc_inum(&ns->ns);
-	if (err) {
-		kfree(ns);
-		return ERR_PTR(err);
-	}
+	if (err)
+		goto fail_free;
 
 	ns->ns.ops = &utsns_operations;
 

@@ -55,6 +68,13 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 	ns->user_ns = get_user_ns(user_ns);
 	up_read(&uts_sem);
 	return ns;
+
+fail_free:
+	kfree(ns);
+fail_dec:
+	dec_uts_namespaces(user_ns);
+fail:
+	return ERR_PTR(err);
 }
 
 /*

@@ -85,6 +105,7 @@ void free_uts_ns(struct kref *kref)
 	struct uts_namespace *ns;
 
 	ns = container_of(kref, struct uts_namespace, kref);
+	dec_uts_namespaces(ns->user_ns);
 	put_user_ns(ns->user_ns);
 	ns_free_inum(&ns->ns);
 	kfree(ns);