From 703286608a220d53584cca5986aad5305eec75ed Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Mon, 8 Aug 2016 14:33:23 -0500
Subject: [PATCH] netns: Add a limit on the number of net namespaces

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 include/linux/user_namespace.h |  1 +
 include/net/net_namespace.h    |  1 +
 kernel/ucount.c                |  1 +
 net/core/net_namespace.c       | 22 +++++++++++++++++++++-
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index d067f0d3038e..c6bc980b06a9 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -29,6 +29,7 @@ enum ucount_type {
 	UCOUNT_PID_NAMESPACES,
 	UCOUNT_UTS_NAMESPACES,
 	UCOUNT_IPC_NAMESPACES,
+	UCOUNT_NET_NAMESPACES,
 	UCOUNT_CGROUP_NAMESPACES,
 	UCOUNT_COUNTS,
 };
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 0933c7455a30..fc4f757107df 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -60,6 +60,7 @@ struct net {
 	struct list_head	exit_list;	/* Use only net_mutex */
 
 	struct user_namespace   *user_ns;	/* Owning user namespace */
+	struct ucounts		*ucounts;
 	spinlock_t		nsid_lock;
 	struct idr		netns_ids;
 
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 335cc5d2cdd7..205f1a07faac 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -71,6 +71,7 @@ static struct ctl_table user_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..3e2812aeceb7 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 struct ucounts *inc_net_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, current_euid(), UCOUNT_NET_NAMESPACES);
+}
+
+static void dec_net_namespaces(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_NET_NAMESPACES);
+}
+
 /*
  * setup_net runs the initializers for the network namespace object.
  */
@@ -351,19 +361,27 @@ void net_drop_ns(void *p)
 struct net *copy_net_ns(unsigned long flags,
 			struct user_namespace *user_ns, struct net *old_net)
 {
+	struct ucounts *ucounts;
 	struct net *net;
 	int rv;
 
 	if (!(flags & CLONE_NEWNET))
 		return get_net(old_net);
 
+	ucounts = inc_net_namespaces(user_ns);
+	if (!ucounts)
+		return ERR_PTR(-ENFILE);
+
 	net = net_alloc();
-	if (!net)
+	if (!net) {
+		dec_net_namespaces(ucounts);
 		return ERR_PTR(-ENOMEM);
+	}
 
 	get_user_ns(user_ns);
 
 	mutex_lock(&net_mutex);
+	net->ucounts = ucounts;
 	rv = setup_net(net, user_ns);
 	if (rv == 0) {
 		rtnl_lock();
@@ -372,6 +390,7 @@ struct net *copy_net_ns(unsigned long flags,
 	}
 	mutex_unlock(&net_mutex);
 	if (rv < 0) {
+		dec_net_namespaces(ucounts);
 		put_user_ns(user_ns);
 		net_drop_ns(net);
 		return ERR_PTR(rv);
@@ -444,6 +463,7 @@ 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->ucounts);
 		put_user_ns(net->user_ns);
 		net_drop_ns(net);
 	}
-- 
2.20.1