lockdown: Lock down TIOCSSERIAL

Lock down TIOCSSERIAL as that can be used to change the ioport and irq
settings on a serial port.  This only appears to be an issue for the serial
drivers that use the core serial code.  All other drivers seem to either
ignore attempts to change port/irq or give an error.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/security.h b/include/linux/security.h
index 683f060..b4a85ba 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -112,6 +112,7 @@ enum lockdown_reason {
 	LOCKDOWN_MSR,
 	LOCKDOWN_ACPI_TABLES,
 	LOCKDOWN_PCMCIA_CIS,
+	LOCKDOWN_TIOCSSERIAL,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };