mntns: Add a limit on the number of mount namespaces.

v2: Fixed the very obvious lack of setting ucounts
    on struct mnt_ns reported by Andrei Vagin, and the kbuild
    test report.

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

1 files changed, 21 insertions, 1 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 7bb2cda3bfef..491b8f3e4c9a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2719,9 +2719,20 @@ dput_out:
 	return retval;
 }
 
+static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
+}
+
+static void dec_mnt_namespaces(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
+}
+
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
 	ns_free_inum(&ns->ns);
+	dec_mnt_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);
 	kfree(ns);
 }
@@ -2738,14 +2749,22 @@ static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 {
 	struct mnt_namespace *new_ns;
+	struct ucounts *ucounts;
 	int ret;
 
+	ucounts = inc_mnt_namespaces(user_ns);
+	if (!ucounts)
+		return ERR_PTR(-ENFILE);
+
 	new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
-	if (!new_ns)
+	if (!new_ns) {
+		dec_mnt_namespaces(ucounts);
 		return ERR_PTR(-ENOMEM);
+	}
 	ret = ns_alloc_inum(&new_ns->ns);
 	if (ret) {
 		kfree(new_ns);
+		dec_mnt_namespaces(ucounts);
 		return ERR_PTR(ret);
 	}
 	new_ns->ns.ops = &mntns_operations;
@@ -2756,6 +2775,7 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 	init_waitqueue_head(&new_ns->poll);
 	new_ns->event = 0;
 	new_ns->user_ns = get_user_ns(user_ns);
+	new_ns->ucounts = ucounts;
 	return new_ns;
 }