net: dsa: ksz: fix skb freeing

The DSA layer frees the original skb when an xmit function returns NULL,
meaning an error occurred. But if the tagging code copied the original
skb, it is responsible of freeing the copy if an error occurs.

The ksz tagging code currently has two issues: if skb_put_padto fails,
the skb copy is not freed, and the original skb will be freed twice.

To fix that, move skb_put_padto inside both branches of the skb_tailroom
condition, before freeing the original skb, and free the copy on error.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Woojung Huh <woojung.huh@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index fab41de8e9837b512709b3c853ffb4831fe08317..de66ca8e620177693e55b54492404d8d3ee52197 100644 (file)
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -42,6 +42,9 @@ static struct sk_buff *ksz_xmit(struct sk_buff *skb, struct net_device *dev)
        padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len;
 
        if (skb_tailroom(skb) >= padlen + KSZ_INGRESS_TAG_LEN) {
+               if (skb_put_padto(skb, skb->len + padlen))
+                       return NULL;
+
                nskb = skb;
        } else {
                nskb = alloc_skb(NET_IP_ALIGN + skb->len +
@@ -56,13 +59,15 @@ static struct sk_buff *ksz_xmit(struct sk_buff *skb, struct net_device *dev)
                skb_set_transport_header(nskb,
                                         skb_transport_header(skb) - skb->head);
                skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
+
+               if (skb_put_padto(nskb, nskb->len + padlen)) {
+                       kfree_skb(nskb);
+                       return NULL;
+               }
+
                kfree_skb(skb);
        }
 
-       /* skb is freed when it fails */
-       if (skb_put_padto(nskb, nskb->len + padlen))
-               return NULL;
-
        tag = skb_put(nskb, KSZ_INGRESS_TAG_LEN);
        tag[0] = 0;
        tag[1] = 1 << p->dp->index; /* destination port */