RE: [PATCH v3] lib/net: fix tcp/udp cksum with padding data

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Kaiwen Deng [mailto:kaiwenx.deng@intel.com]
> Sent: Tuesday, 12 December 2023 03.16
> 
> IEEE 802 packets may have a minimum size limit. The data fields
> should be padded when necessary. In some cases, the padding data
> is not zero.
> 
> In 'rte_ipv4_udptcp_cksum_mbuf()', as payload length
> "mbuf->pkt_len - l4_off" is used, which includes padding and if
> padding is not zero it will end up producing wrong checksum.
> 
> This patch will use IP header to get the payload size to calculate
> tcp/udp checksum.
> 
> Fixes: d178f693bbfe ("net: add UDP/TCP checksum in mbuf segments")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Kaiwen Deng <kaiwenx.deng@intel.com>
> ---
>  lib/net/rte_ip.h | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index 6fa98a5a0f..c503a2b57f 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -423,7 +423,10 @@ __rte_ipv4_udptcp_cksum_mbuf(const struct rte_mbuf
> *m,
>  	if (l4_off > m->pkt_len)
>  		return 0;

It's not directly related, but while you are at it, please also add unlikely to the above check:

-	if (l4_off > m->pkt_len)
-		return 0;
+	if (unlikely(l4_off > m->pkt_len))
+		return 0; /* invalid params, return a dummy value */

> 
> -	if (rte_raw_cksum_mbuf(m, l4_off, m->pkt_len - l4_off,
> &raw_cksum))
> +	uint16_t len = rte_be_to_cpu_16(ipv4_hdr->total_length) -
> +				(uint16_t)rte_ipv4_hdr_len(ipv4_hdr);
> +
> +	if (rte_raw_cksum_mbuf(m, l4_off, len, &raw_cksum))

Please declare "uint16_t len;" with the other variables at the top of the function, and only set its value here. (It's allowed to declare here, but please follow this function's existing convention of where variables are declared.)

>  		return 0;
> 
>  	cksum = raw_cksum + rte_ipv4_phdr_cksum(ipv4_hdr, 0);
> @@ -666,7 +669,9 @@ __rte_ipv6_udptcp_cksum_mbuf(const struct rte_mbuf
> *m,
>  	if (l4_off > m->pkt_len)
>  		return 0;

Again not directly related, but please also add unlikely to this comparison:

-	if (l4_off > m->pkt_len)
-		return 0;
+	if (unlikely(l4_off > m->pkt_len))
+		return 0; /* invalid params, return a dummy value */

> 
> -	if (rte_raw_cksum_mbuf(m, l4_off, m->pkt_len - l4_off,
> &raw_cksum))
> +	uint16_t len = rte_be_to_cpu_16(ipv6_hdr->payload_len);
> +
> +	if (rte_raw_cksum_mbuf(m, l4_off, len, &raw_cksum))

No need for "len" variable here, just use rte_be_to_cpu_16(ipv6_hdr->payload_len) directly:

-	if (rte_raw_cksum_mbuf(m, l4_off, m->pkt_len - l4_off, &raw_cksum))
+	if (rte_raw_cksum_mbuf(m, l4_off, rte_be_to_cpu_16(ipv6_hdr->payload_len), &raw_cksum))

>  		return 0;
> 
>  	cksum = raw_cksum + rte_ipv6_phdr_cksum(ipv6_hdr, 0);
> --
> 2.34.1