[PATCH 09/10] netns: Add a limit on the number of net namespaces

["Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>]

Signed-off-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
---
 include/linux/user_namespace.h |  1 +
 kernel/user_namespace.c        |  1 +
 net/core/net_namespace.c       | 15 +++++++++++++++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 3ad3cb505781..785a7ca2731b 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -27,6 +27,7 @@ enum ucounts {
 	UCOUNT_PID_NAMESPACES,
 	UCOUNT_UTS_NAMESPACES,
 	UCOUNT_IPC_NAMESPACES,
+	UCOUNT_NET_NAMESPACES,
 	UCOUNT_CGROUP_NAMESPACES,
 	UCOUNT_MAX,
 };
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index c150765c328e..23a70d66a310 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -80,6 +80,7 @@ static struct ctl_table userns_table[] = {
 	UCOUNT_ENTRY("max_pid_namespaces"),
 	UCOUNT_ENTRY("max_uts_namespaces"),
 	UCOUNT_ENTRY("max_ipc_namespaces"),
+	UCOUNT_ENTRY("max_net_namespaces"),
 	UCOUNT_ENTRY("max_cgroup_namespaces"),
 	{ }
 };
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 2c2eb1b629b1..a489f192d619 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -266,6 +266,16 @@ struct net *get_net_ns_by_id(struct net *net, int id)
 	return peer;
 }
 
+static bool inc_net_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, UCOUNT_NET_NAMESPACES);
+}
+
+static void dec_net_namespaces(struct user_namespace *ns)
+{
+	dec_ucount(ns, UCOUNT_NET_NAMESPACES);
+}
+
 /*
  * setup_net runs the initializers for the network namespace object.
  */
@@ -276,6 +286,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	int error = 0;
 	LIST_HEAD(net_exit_list);
 
+	if (!inc_net_namespaces(user_ns))
+		return -ENFILE;
+
 	atomic_set(&net->count, 1);
 	atomic_set(&net->passive, 1);
 	net->dev_base_seq = 1;
@@ -372,6 +385,7 @@ struct net *copy_net_ns(unsigned long flags,
 	}
 	mutex_unlock(&net_mutex);
 	if (rv < 0) {
+		dec_net_namespaces(user_ns);
 		put_user_ns(user_ns);
 		net_drop_ns(net);
 		return ERR_PTR(rv);
@@ -444,6 +458,7 @@ static void cleanup_net(struct work_struct *work)
 	/* Finally it is safe to free my network namespace structure */
 	list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {
 		list_del_init(&net->exit_list);
+		dec_net_namespaces(net->user_ns);
 		put_user_ns(net->user_ns);
 		net_drop_ns(net);
 	}
-- 
2.8.3