2021-07-21 23:58:02

by Lino Sanfilippo

Subject: [PATCH v2 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum

If the checksum calculation is offloaded to the network device (e.g due to
NETIF_F_HW_CSUM inherited from the DSA master device), the calculated
layer 4 checksum is incorrect. This is since the DSA tag which is placed
after the layer 4 data is considered as being part of the daa and thus
errorneously included into the checksum calculation.
To avoid this, always calculate the layer 4 checksum in software.

Signed-off-by: Lino Sanfilippo <[email protected]>
---
net/dsa/tag_ksz.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index 53565f48934c..a201ccf2435d 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -53,6 +53,9 @@ static struct sk_buff *ksz8795_xmit(struct sk_buff *skb, struct net_device *dev)
u8 *tag;
u8 *addr;

+ if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
+ return NULL;
+
/* Tag encoding */
tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
addr = skb_mac_header(skb);
@@ -114,6 +117,9 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
u8 *addr;
u16 val;

+ if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
+ return NULL;
+
/* Tag encoding */
tag = skb_put(skb, KSZ9477_INGRESS_TAG_LEN);
addr = skb_mac_header(skb);
@@ -164,6 +170,9 @@ static struct sk_buff *ksz9893_xmit(struct sk_buff *skb,
u8 *addr;
u8 *tag;

+ if (skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_help(skb))
+ return NULL;
+
/* Tag encoding */
tag = skb_put(skb, KSZ_INGRESS_TAG_LEN);
addr = skb_mac_header(skb);
--
2.32.0

2021-07-22 03:59:49

by Florian Fainelli

Subject: Re: [PATCH v2 2/2] net: dsa: tag_ksz: dont let the hardware process the layer 4 checksum

On 7/21/2021 2:56 PM, Lino Sanfilippo wrote:
> If the checksum calculation is offloaded to the network device (e.g due to
> NETIF_F_HW_CSUM inherited from the DSA master device), the calculated
> layer 4 checksum is incorrect. This is since the DSA tag which is placed
> after the layer 4 data is considered as being part of the daa and thus
> errorneously included into the checksum calculation.
> To avoid this, always calculate the layer 4 checksum in software.
>
> Signed-off-by: Lino Sanfilippo <[email protected]>

Reviewed-by: Florian Fainelli <[email protected]>
--
Florian