send: simplify skb_padding with nice macro

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/src/send.c b/src/send.c
index 9c9f694..9b1aec0 100644
--- a/src/send.c
+++ b/src/send.c
@@ -112,12 +112,11 @@ static inline void keep_key_fresh(struct wireguard_peer *peer)
 static inline unsigned int skb_padding(struct sk_buff *skb)
 {
 	/* We do this modulo business with the MTU, just in case the networking layer
-	 * gives us a packet that's bigger than the MTU. Since we support GSO, this
-	 * isn't strictly neccessary, but it's better to be cautious here, especially
-	 * if that code ever changes.
+	 * gives us a packet that's bigger than the MTU. In that case, we wouldn't want
+	 * the final subtraction to overflow in the case of the padded_size being clamped.
 	 */
 	unsigned int last_unit = skb->len % PACKET_CB(skb)->mtu;
-	unsigned int padded_size = (last_unit + MESSAGE_PADDING_MULTIPLE - 1) & ~(MESSAGE_PADDING_MULTIPLE - 1);
+	unsigned int padded_size = ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE);
 
 	if (padded_size > PACKET_CB(skb)->mtu)
 		padded_size = PACKET_CB(skb)->mtu;