[PATCH v2 08/10] cgroupns: Add a limit on the number of cgroup namespaces

[Eric W. Biederman]

Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
---
 include/linux/user_namespace.h |  1 +
 kernel/cgroup.c                | 15 +++++++++++++++
 kernel/user_namespace.c        |  1 +
 3 files changed, 17 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 367cf08ff63d..1a3a9cb93277 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_CGROUP_NAMESPACES,
        UCOUNT_COUNTS,
 };
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 86cb5c6e8932..240eec43390b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6260,6 +6260,16 @@ void cgroup_sk_free(struct sock_cgroup_data *skcd)
 
 /* cgroup namespaces */
 
+static bool inc_cgroup_namespaces(struct user_namespace *ns)
+{
+       return inc_ucount(ns, UCOUNT_CGROUP_NAMESPACES);
+}
+
+static void dec_cgroup_namespaces(struct user_namespace *ns)
+{
+       dec_ucount(ns, UCOUNT_CGROUP_NAMESPACES);
+}
+
 static struct cgroup_namespace *alloc_cgroup_ns(void)
 {
        struct cgroup_namespace *new_ns;
@@ -6281,6 +6291,7 @@ 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->user_ns);
        put_user_ns(ns->user_ns);
        ns_free_inum(&ns->ns);
        kfree(ns);
@@ -6305,6 +6316,9 @@ struct cgroup_namespace *copy_cgroup_ns(unsigned long 
flags,
        if (!ns_capable(user_ns, CAP_SYS_ADMIN))
                return ERR_PTR(-EPERM);
 
+       if (!inc_cgroup_namespaces(user_ns))
+               return ERR_PTR(-ENFILE);
+
        mutex_lock(&cgroup_mutex);
        spin_lock_bh(&css_set_lock);
 
@@ -6317,6 +6331,7 @@ 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(user_ns);
                return new_ns;
        }
 
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 060d3e099f87..1cf074cb47e2 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_cgroup_namespaces"),
        { }
 };
 #endif /* CONFIG_SYSCTL */
-- 
2.8.3