[PATCH net] net: dsa: tag_rtl4_a: fix egress tags

[DENG Qingfang]

Commit 86dd9868b878 has several issues, but was accepted too soon
before anyone could take a look.

- Double free. dsa_slave_xmit() will free the skb if the xmit function
  returns NULL, but the skb is already freed by eth_skb_pad(). Use
  __skb_put_padto() to avoid that.
- Unnecessary allocation. It has been done by DSA core since commit
  a3b0b6479700.
- A u16 pointer points to skb data. It should be __be16 for network
  byte order.
- Typo in comments. "numer" -> "number".

Fixes: 86dd9868b878 ("net: dsa: tag_rtl4_a: Support also egress tags")
Signed-off-by: DENG Qingfang <dqfext@xxxxxxxxx>
---
 net/dsa/tag_rtl4_a.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/dsa/tag_rtl4_a.c b/net/dsa/tag_rtl4_a.c
index c17d39b4a1a0..e9176475bac8 100644
--- a/net/dsa/tag_rtl4_a.c
+++ b/net/dsa/tag_rtl4_a.c
@@ -35,14 +35,12 @@ static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
 				      struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
+	__be16 *p;
 	u8 *tag;
-	u16 *p;
 	u16 out;
 
 	/* Pad out to at least 60 bytes */
-	if (unlikely(eth_skb_pad(skb)))
-		return NULL;
-	if (skb_cow_head(skb, RTL4_A_HDR_LEN) < 0)
+	if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
 		return NULL;
 
 	netdev_dbg(dev, "add realtek tag to package to port %d\n",
@@ -53,13 +51,13 @@ static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
 	tag = skb->data + 2 * ETH_ALEN;
 
 	/* Set Ethertype */
-	p = (u16 *)tag;
+	p = (__be16 *)tag;
 	*p = htons(RTL4_A_ETHERTYPE);
 
 	out = (RTL4_A_PROTOCOL_RTL8366RB << 12) | (2 << 8);
-	/* The lower bits is the port numer */
+	/* The lower bits is the port number */
 	out |= (u8)dp->index;
-	p = (u16 *)(tag + 2);
+	p = (__be16 *)(tag + 2);
 	*p = htons(out);
 
 	return skb;
-- 
2.25.1