utsns: Add a limit on the number of uts namespaces

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

4 files changed, 32 insertions, 5 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9ee94827728d..f9df7dd2609a 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -27,6 +27,7 @@ struct ucounts;
 enum ucount_type {
         UCOUNT_USER_NAMESPACES,
         UCOUNT_PID_NAMESPACES,
+        UCOUNT_UTS_NAMESPACES,
         UCOUNT_COUNTS,
 };
 
diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index 5093f58ae192..60f0bb83b313 100644
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -24,6 +24,7 @@ struct uts_namespace {
         struct kref kref;
         struct new_utsname name;
         struct user_namespace *user_ns;
+        struct ucounts *ucounts;
         struct ns_common ns;
 };
 extern struct uts_namespace init_uts_ns;
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 66eca94e4ada..866850e2eb92 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -69,6 +69,7 @@ static int int_max = INT_MAX;
 static struct ctl_table user_table[] = {
         UCOUNT_ENTRY("max_user_namespaces"),
         UCOUNT_ENTRY("max_pid_namespaces"),
+        UCOUNT_ENTRY("max_uts_namespaces"),
         { }
 };
 #endif /* CONFIG_SYSCTL */
diff --git a/kernel/utsname.c b/kernel/utsname.c
index 831ea7108232..f3b0bb4ac3ba 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -17,6 +17,16 @@
 #include <linux/user_namespace.h>
 #include <linux/proc_ns.h>
 
+static struct ucounts *inc_uts_namespaces(struct user_namespace *ns)
+{
+        return inc_ucount(ns, current_euid(), UCOUNT_UTS_NAMESPACES);
+}
+
+static void dec_uts_namespaces(struct ucounts *ucounts)
+{
+        dec_ucount(ucounts, UCOUNT_UTS_NAMESPACES);
+}
+
 static struct uts_namespace *create_uts_ns(void)
 {
         struct uts_namespace *uts_ns;
@@ -36,18 +46,24 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
                                           struct uts_namespace *old_ns)
 {
         struct uts_namespace *ns;
+        struct ucounts *ucounts;
         int err;
 
+        err = -ENFILE;
+        ucounts = inc_uts_namespaces(user_ns);
+        if (!ucounts)
+                goto fail;
+
+        err = -ENOMEM;
         ns = create_uts_ns();
         if (!ns)
-                return ERR_PTR(-ENOMEM);
+                goto fail_dec;
 
         err = ns_alloc_inum(&ns->ns);
-        if (err) {
-                kfree(ns);
-                return ERR_PTR(err);
-        }
+        if (err)
+                goto fail_free;
 
+        ns->ucounts = ucounts;
         ns->ns.ops = &utsns_operations;
 
         down_read(&uts_sem);
@@ -55,6 +71,13 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
         ns->user_ns = get_user_ns(user_ns);
         up_read(&uts_sem);
         return ns;
+
+fail_free:
+        kfree(ns);
+fail_dec:
+        dec_uts_namespaces(ucounts);
+fail:
+        return ERR_PTR(err);
 }
 
 /*
@@ -85,6 +108,7 @@ void free_uts_ns(struct kref *kref)
         struct uts_namespace *ns;
 
         ns = container_of(kref, struct uts_namespace, kref);
+        dec_uts_namespaces(ns->ucounts);
         put_user_ns(ns->user_ns);
         ns_free_inum(&ns->ns);
         kfree(ns);