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

DENG Qingfang
2021-02-28T17:09:33Z

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@gmail.com>
---
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