cgroupns: Add a limit on the number of cgroup namespaces

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

4 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 984f73b719a9..1ed92812785a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -621,6 +621,7 @@ struct cgroup_namespace {
         atomic_t                count;
         struct ns_common        ns;
         struct user_namespace   *user_ns;
+        struct ucounts          *ucounts;
         struct css_set          *root_cset;
 };
 
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index e1d672186f00..d067f0d3038e 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_CGROUP_NAMESPACES,
         UCOUNT_COUNTS,
 };
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7f5221..e9e4427fec46 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6295,6 +6295,16 @@ void cgroup_sk_free(struct sock_cgroup_data *skcd)
 
 /* cgroup namespaces */
 
+static struct ucounts *inc_cgroup_namespaces(struct user_namespace *ns)
+{
+        return inc_ucount(ns, current_euid(), UCOUNT_CGROUP_NAMESPACES);
+}
+
+static void dec_cgroup_namespaces(struct ucounts *ucounts)
+{
+        dec_ucount(ucounts, UCOUNT_CGROUP_NAMESPACES);
+}
+
 static struct cgroup_namespace *alloc_cgroup_ns(void)
 {
         struct cgroup_namespace *new_ns;
@@ -6316,6 +6326,7 @@ static struct cgroup_namespace *alloc_cgroup_ns(void)
 void free_cgroup_ns(struct cgroup_namespace *ns)
 {
         put_css_set(ns->root_cset);
+        dec_cgroup_namespaces(ns->ucounts);
         put_user_ns(ns->user_ns);
         ns_free_inum(&ns->ns);
         kfree(ns);
@@ -6327,6 +6338,7 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
                                         struct cgroup_namespace *old_ns)
 {
         struct cgroup_namespace *new_ns;
+        struct ucounts *ucounts;
         struct css_set *cset;
 
         BUG_ON(!old_ns);
@@ -6340,6 +6352,10 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
         if (!ns_capable(user_ns, CAP_SYS_ADMIN))
                 return ERR_PTR(-EPERM);
 
+        ucounts = inc_cgroup_namespaces(user_ns);
+        if (!ucounts)
+                return ERR_PTR(-ENFILE);
+
         /* It is not safe to take cgroup_mutex here */
         spin_lock_irq(&css_set_lock);
         cset = task_css_set(current);
@@ -6349,10 +6365,12 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long flags,
         new_ns = alloc_cgroup_ns();
         if (IS_ERR(new_ns)) {
                 put_css_set(cset);
+                dec_cgroup_namespaces(ucounts);
                 return new_ns;
         }
 
         new_ns->user_ns = get_user_ns(user_ns);
+        new_ns->ucounts = ucounts;
         new_ns->root_cset = cset;
 
         return new_ns;
diff --git a/kernel/ucount.c b/kernel/ucount.c
index fbab75424da6..335cc5d2cdd7 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_cgroup_namespaces"),
         { }
 };
 #endif /* CONFIG_SYSCTL */