macsec: limit replay window size with XPN

IEEE 802.1AEbw-2013 (section 10.7.8) specifies that the maximum value
of the replay window is 2^30-1, to help with recovery of the upper
bits of the PN.

To avoid leaving the existing macsec device in an inconsistent state
if this test fails during changelink, reuse the cleanup mechanism
introduced for HW offload. This wasn't needed until now because
macsec_changelink_common could not fail during changelink, as
modifying the cipher suite was not allowed.

Finally, this must happen after handling IFLA_MACSEC_CIPHER_SUITE so
that secy->xpn is set.

Fixes: 48ef50f ("macsec: Netlink support of XPN cipher suites (IEEE 802.1AEbw)")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: qsn

drivers/net/macsec.c

@@ -243,6 +243,7 @@ static struct macsec_cb *macsec_skb_cb(struct sk_buff *skb)
 #define DEFAULT_SEND_SCI true
 #define DEFAULT_ENCRYPT false
 #define DEFAULT_ENCODING_SA 0
+#define MACSEC_XPN_MAX_REPLAY_WINDOW (((1 << 30) - 1))
 
 static bool send_sci(const struct macsec_secy *secy)
 {
@@ -3746,9 +3747,6 @@ static int macsec_changelink_common(struct net_device *dev,
 		secy->operational = tx_sa && tx_sa->active;
 	}
 
-	if (data[IFLA_MACSEC_WINDOW])
-		secy->replay_window = nla_get_u32(data[IFLA_MACSEC_WINDOW]);
-
 	if (data[IFLA_MACSEC_ENCRYPT])
 		tx_sc->encrypt = !!nla_get_u8(data[IFLA_MACSEC_ENCRYPT]);
 
@@ -3794,6 +3792,16 @@ static int macsec_changelink_common(struct net_device *dev,
 		}
 	}
 
+	if (data[IFLA_MACSEC_WINDOW]) {
+		secy->replay_window = nla_get_u32(data[IFLA_MACSEC_WINDOW]);
+
+		/* IEEE 802.1AEbw-2013 10.7.8 - maximum replay window
+		 * for XPN cipher suites */
+		if (secy->xpn &&
+		    secy->replay_window > MACSEC_XPN_MAX_REPLAY_WINDOW)
+			return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -3823,7 +3831,7 @@ static int macsec_changelink(struct net_device *dev, struct nlattr *tb[],
 
 	ret = macsec_changelink_common(dev, data);
 	if (ret)
-		return ret;
+		goto cleanup;
 
 	/* If h/w offloading is available, propagate to the device */
 	if (macsec_is_offloaded(macsec)) {