[PATCH net] net: dsa: ksz: fix skb freeing

[PATCH net] net: dsa: ksz: fix skb freeing

[Vivien Didelot]

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>
---
 net/dsa/tag_ksz.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index fab41de8e983..de66ca8e6201 100644
--- 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 */
-- 
2.14.0

Re: [PATCH net] net: dsa: ksz: fix skb freeing

[Andrew Lunn]

Hi Vivien

You missed sending a copy to Woojung Huh.

    Andrew

On Wed, Aug 09, 2017 at 04:46:09PM -0400, Vivien Didelot wrote:
> 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>
> ---
>  net/dsa/tag_ksz.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
> index fab41de8e983..de66ca8e6201 100644
> --- 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 */
> -- 
> 2.14.0
> 

RE: [PATCH net] net: dsa: ksz: fix skb freeing

[Woojung.Huh]

> 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>

Re: [PATCH net] net: dsa: ksz: fix skb freeing

[David Miller]

From: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Date: Wed,  9 Aug 2017 16:46:09 -0400

> 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>

Applied, thanks.