Re: [PATCH 07/24] ip: introduce functions to compute the header part checksum for TCP/UDP

[Stefano Brivio <sbrivio@redhat.com>]

On Fri,  2 Feb 2024 15:11:34 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> The TCP and UDP checksums are computed using the data in the TCP/UDP
> payload but also some informations in the IP header (protocol,
> length, source and destination addresses).
> 
> We add two functions, proto_ipv4_header_checksum() and
> proto_ipv6_header_checksum(), to compute the checksum of the IP
> header part.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  ip.h  | 24 ++++++++++++++++++++++++
>  tcp.c | 40 +++++++++++++++-------------------------
>  udp.c |  6 ++----
>  3 files changed, 41 insertions(+), 29 deletions(-)
> 
> diff --git a/ip.h b/ip.h
> index ff7902c45a95..87cb8dd21d2e 100644
> --- a/ip.h
> +++ b/ip.h
> @@ -97,4 +97,28 @@ static inline uint16_t ipv4_hdr_checksum(struct iphdr *iph, int proto)
>  
>  	return ~csum_fold(sum);
>  }
> +
> +static inline uint32_t proto_ipv4_header_checksum(struct iphdr *iph, int proto)

Function comments, proto can be uint8_t for consistency, and probably
all these don't need to be inlines. Interesting readings in case you
haven't come across them:

	https://lwn.net/Kernel/Index/#Inline_functions
	https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?id=6d280f4d760e3bcb4a8df302afebf085b65ec982#n962

> +{
> +	uint32_t sum = htons(proto);
> +
> +	sum += (iph->saddr >> 16) & 0xffff;
> +	sum += iph->saddr & 0xffff;
> +	sum += (iph->daddr >> 16) & 0xffff;
> +	sum += iph->daddr & 0xffff;
> +	sum += htons(ntohs(iph->tot_len) - 20);
> +
> +	return sum;
> +}
> +
> +static inline uint32_t proto_ipv6_header_checksum(struct ipv6hdr *ip6h,
> +						  int proto)
> +{
> +	uint32_t sum = htons(proto) + ip6h->payload_len;
> +
> +	sum += sum_16b(&ip6h->saddr, sizeof(ip6h->saddr));
> +	sum += sum_16b(&ip6h->daddr, sizeof(ip6h->daddr));
> +
> +	return sum;
> +}
>  #endif /* IP_H */
> diff --git a/tcp.c b/tcp.c
> index 293ab12d8c21..2fd6bc2eda53 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -938,39 +938,25 @@ static void tcp_sock_set_bufsize(const struct ctx *c, int s)
>   * tcp_update_check_tcp4() - Update TCP checksum from stored one
>   * @buf:	L2 packet buffer with final IPv4 header
>   */
> -static void tcp_update_check_tcp4(struct tcp4_l2_buf_t *buf)
> +static uint16_t tcp_update_check_tcp4(struct iphdr *iph)
>  {
> -	uint16_t tlen = ntohs(buf->iph.tot_len) - 20;
> -	uint32_t sum = htons(IPPROTO_TCP);
> +	struct tcphdr *th = (void *)(iph + 1);
> +	uint16_t tlen = ntohs(iph->tot_len) - 20;
> +	uint32_t sum = proto_ipv4_header_checksum(iph, IPPROTO_TCP);
>  
> -	sum += (buf->iph.saddr >> 16) & 0xffff;
> -	sum += buf->iph.saddr & 0xffff;
> -	sum += (buf->iph.daddr >> 16) & 0xffff;
> -	sum += buf->iph.daddr & 0xffff;
> -	sum += htons(ntohs(buf->iph.tot_len) - 20);
> -
> -	buf->th.check = 0;
> -	buf->th.check = csum(&buf->th, tlen, sum);
> +	return csum(th, tlen, sum);
>  }
>  
>  /**
>   * tcp_update_check_tcp6() - Calculate TCP checksum for IPv6
>   * @buf:	L2 packet buffer with final IPv6 header
>   */
> -static void tcp_update_check_tcp6(struct tcp6_l2_buf_t *buf)
> +static uint16_t tcp_update_check_tcp6(struct ipv6hdr *ip6h)
>  {
> -	int len = ntohs(buf->ip6h.payload_len) + sizeof(struct ipv6hdr);
> -
> -	buf->ip6h.hop_limit = IPPROTO_TCP;
> -	buf->ip6h.version = 0;
> -	buf->ip6h.nexthdr = 0;
> +	struct tcphdr *th = (void *)(ip6h + 1);
> +	uint32_t sum = proto_ipv6_header_checksum(ip6h, IPPROTO_TCP);
>  
> -	buf->th.check = 0;
> -	buf->th.check = csum(&buf->ip6h, len, 0);
> -
> -	buf->ip6h.hop_limit = 255;
> -	buf->ip6h.version = 6;
> -	buf->ip6h.nexthdr = IPPROTO_TCP;
> +	return csum(th, ntohs(ip6h->payload_len), sum);
>  }
>  
>  /**
> @@ -1381,7 +1367,7 @@ do {									\
>  
>  		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
>  
> -		tcp_update_check_tcp4(b);
> +		b->th.check = tcp_update_check_tcp4(&b->iph);
>  
>  		tlen = tap_iov_len(c, &b->taph, ip_len);
>  	} else {
> @@ -1400,7 +1386,11 @@ do {									\
>  
>  		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
>  
> -		tcp_update_check_tcp6(b);
> +		b->th.check = tcp_update_check_tcp6(&b->ip6h);
> +
> +		b->ip6h.hop_limit = 255;
> +		b->ip6h.version = 6;
> +		b->ip6h.nexthdr = IPPROTO_TCP;
>  
>  		b->ip6h.flow_lbl[0] = (conn->sock >> 16) & 0xf;
>  		b->ip6h.flow_lbl[1] = (conn->sock >> 8) & 0xff;
> diff --git a/udp.c b/udp.c
> index 6f867df81c05..96b4e6ca9a85 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -669,10 +669,8 @@ static size_t udp_update_hdr6(const struct ctx *c, int n, in_port_t dstport,
>  	b->uh.source = b->s_in6.sin6_port;
>  	b->uh.dest = htons(dstport);
>  	b->uh.len = b->ip6h.payload_len;
> -
> -	b->ip6h.hop_limit = IPPROTO_UDP;
> -	b->ip6h.version = b->ip6h.nexthdr = b->uh.check = 0;
> -	b->uh.check = csum(&b->ip6h, ip_len, 0);
> +	b->uh.check = csum(&b->uh, ntohs(b->ip6h.payload_len),
> +			 proto_ipv6_header_checksum(&b->ip6h, IPPROTO_UDP));
>  	b->ip6h.version = 6;
>  	b->ip6h.nexthdr = IPPROTO_UDP;
>  	b->ip6h.hop_limit = 255;

-- 
Stefano