Creds: creds->security can be NULL is selinux is disabled

__validate_process_creds should check if selinux is actually enabled before
running tests on the selinux portion of the credentials struct.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 24520a5..fb37160 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -15,6 +15,7 @@
 #include <linux/capability.h>
 #include <linux/init.h>
 #include <linux/key.h>
+#include <linux/selinux.h>
 #include <asm/atomic.h>
 
 struct user_struct;
@@ -182,11 +183,13 @@
 	if (atomic_read(&cred->usage) < atomic_read(&cred->subscribers))
 		return true;
 #ifdef CONFIG_SECURITY_SELINUX
-	if ((unsigned long) cred->security < PAGE_SIZE)
-		return true;
-	if ((*(u32*)cred->security & 0xffffff00) ==
-	    (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
-		return true;
+	if (selinux_is_enabled()) {
+		if ((unsigned long) cred->security < PAGE_SIZE)
+			return true;
+		if ((*(u32 *)cred->security & 0xffffff00) ==
+		    (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
+			return true;
+	}
 #endif
 	return false;
 }