macsec: limit ICV length to 16 octets

IEEE 802.1AE-2006 standard recommends that the ICV element in a MACsec
frame should not exceed 16 octets: add MACSEC_STD_ICV_LEN in uapi
definitions accordingly, and avoid accepting configurations where the ICV
length exceeds the standard value. Leave definition of MACSEC_MAX_ICV_LEN
unchanged for backwards compatibility with userspace programs.

Fixes: dece8d2b78 ("uapi: add MACsec bits")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macsec.c

@@ -510,7 +510,7 @@ static bool macsec_validate_skb(struct sk_buff *skb, u16 icv_len)
 }
 
 #define MACSEC_NEEDED_HEADROOM (macsec_extra_len(true))
-#define MACSEC_NEEDED_TAILROOM MACSEC_MAX_ICV_LEN
+#define MACSEC_NEEDED_TAILROOM MACSEC_STD_ICV_LEN
 
 static void macsec_fill_iv(unsigned char *iv, sci_t sci, u32 pn)
 {
@@ -3217,7 +3217,7 @@ static int macsec_validate_attr(struct nlattr *tb[], struct nlattr *data[])
 	case MACSEC_DEFAULT_CIPHER_ID:
 	case MACSEC_DEFAULT_CIPHER_ALT:
 		if (icv_len < MACSEC_MIN_ICV_LEN ||
-		    icv_len > MACSEC_MAX_ICV_LEN)
+		    icv_len > MACSEC_STD_ICV_LEN)
 			return -EINVAL;
 		break;
 	default:

include/uapi/linux/if_macsec.h

@@ -26,6 +26,8 @@
 
 #define MACSEC_MIN_ICV_LEN 8
 #define MACSEC_MAX_ICV_LEN 32
+/* upper limit for ICV length as recommended by IEEE802.1AE-2006 */
+#define MACSEC_STD_ICV_LEN 16
 
 enum macsec_attrs {
 	MACSEC_ATTR_UNSPEC,