[PATCH 3.16 107/328] net: mac802154: tx: expand tailroom if necessary

[Ben Hutchings]

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alexander Aring <aring@xxxxxxxxxxxx>

commit f9c52831133050c6b82aa8b6831c92da2bbf2a0b upstream.

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 <david.palma@xxxxxxx>
Reported-by: Rabi Narayan Sahoo <rabinarayans0828@xxxxxxxxx>
Signed-off-by: Alexander Aring <aring@xxxxxxxxxxxx>
Signed-off-by: Stefan Schmidt <stefan@xxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Substitute literal number for IEEE802154_FCS_LEN
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/mac802154/tx.c
+++ b/net/mac802154/tx.c
@@ -96,8 +96,20 @@ netdev_tx_t mac802154_tx(struct mac80215
 	mac802154_monitors_rx(mac802154_to_priv(&priv->hw), skb);
 
 	if (!(priv->hw.flags & IEEE802154_HW_OMIT_CKSUM)) {
-		u16 crc = crc_ccitt(0, skb->data, skb->len);
+		struct sk_buff *nskb;
+		u16 crc;
 
+		if (unlikely(skb_tailroom(skb) < 2)) {
+			nskb = skb_copy_expand(skb, 0, 2, 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));
 	}