diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c
index 6f88b507f927..6bf3e2da7bda 100644
--- a/security/keys/user_defined.c
+++ b/security/keys/user_defined.c
@@ -61,7 +61,8 @@ int user_preparse(struct key_preparsed_payload *prep)
 	struct user_key_payload *upayload;
 	size_t datalen = prep->datalen;
 
-	if (datalen == 0 || datalen > 32767 || !prep->data)
+	if (datalen == 0 || datalen > 32767 || datalen < 4 ||
+	    !prep->data)
 		return -EINVAL;
 
 	upayload = kmalloc_flex(*upayload, data, datalen);