[PATCH net v2 2/2] net: dsa: skb_put_padto() already frees nskb

[Florian Fainelli]

The first call of skb_put_padto() will free up the SKB on error, but we
return NULL which tells dsa_slave_xmit() that the original SKB should be
freed so this would lead to a double free here.

The second skb_put_padto() already frees the passed sk_buff reference
upon error, so calling kfree_skb() on it again is not necessary.

Detected by CoverityScan, CID#1416687 ("USE_AFTER_FREE")

Fixes: e71cb9e00922 ("net: dsa: ksz: fix skb freeing")
Signed-off-by: Florian Fainelli <f.faine...@gmail.com>
---
 net/dsa/tag_ksz.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index de66ca8e6201..3bd6e2a83125 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -42,7 +42,8 @@ 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))
+               /* Let dsa_slave_xmit() free skb */
+               if (__skb_put_padto(skb, skb->len + padlen, false))
                        return NULL;
 
                nskb = skb;
@@ -60,10 +61,11 @@ static struct sk_buff *ksz_xmit(struct sk_buff *skb, struct 
net_device *dev)
                                         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);
+               /* Let skb_put_padto() free nskb, and let dsa_slave_xmit() free
+                * skb
+                */
+               if (skb_put_padto(nskb, nskb->len + padlen))
                        return NULL;
-               }
 
                kfree_skb(skb);
        }
-- 
2.9.3