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>

4 files changed, 24 insertions, 1 deletions

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);
         }