net: mac802154: tx: expand tailroom if necessary

This patch is necessary if case of AF_PACKET or other socket interface
which I am aware of it and didn't allocated the necessary room.

Reported-by: David Palma <[e-mail]>
Reported-by: Rabi Narayan Sahoo <[e-mail]>
Cc: [e-mail]
Signed-off-by: Alexander Aring <[e-mail]>
Signed-off-by: Stefan Schmidt <[e-mail]>

net/mac802154/tx.c

···
 	int ret;
 
 	if (!(local->hw.flags & IEEE802154_HW_TX_OMIT_CKSUM)) {
-		u16 crc = crc_ccitt(0, skb->data, skb->len);
+		struct sk_buff *nskb;
+		u16 crc;
 
+		if (unlikely(skb_tailroom(skb) < IEEE802154_FCS_LEN)) {
+			nskb = skb_copy_expand(skb, 0, IEEE802154_FCS_LEN,
+					       GFP_ATOMIC);
+			if (likely(nskb)) {
+				consume_skb(skb);
+				skb = nskb;
+			} else {
+				goto err_tx;
+			}
+		}
+
+		crc = crc_ccitt(0, skb->data, skb->len);
 		put_unaligned_le16(crc, skb_put(skb, 2));
 	}