Re: [PATCH v3 7/9] checksum: introduce functions to compute the header part checksum for TCP/UDP

[David Gibson <david@gibson.dropbear.id.au>]

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On Sat, Feb 17, 2024 at 04:07:23PM +0100, Laurent Vivier 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_psum() and
> proto_ipv6_header_psum(), to compute the checksum of the IP
> header part.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> 
> Notes:
>     v3:
>       - function parameters provide tot_len, saddr, daddr and protocol
>         rather than an iphdr/ipv6hdr
>     
>     v2:
>       - move new function to checksum.c
>       - use _psum rather than _checksum in the name
>       - replace csum_udp4() and csum_udp6() by the new function
> 
>  checksum.c | 67 ++++++++++++++++++++++++++++++++++++++++++------------
>  checksum.h |  4 ++++
>  tcp.c      | 44 ++++++++++++++++-------------------
>  udp.c      | 10 ++++----
>  4 files changed, 81 insertions(+), 44 deletions(-)
> 
> diff --git a/checksum.c b/checksum.c
> index 511b296a9a80..55bf1340a257 100644
> --- a/checksum.c
> +++ b/checksum.c
> @@ -134,6 +134,30 @@ uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
>  	return ~csum_fold(sum);
>  }
>  
> +/**
> + * proto_ipv4_header_psum() - Calculates the partial checksum of an
> + * 			      IPv4 header for UDP or TCP
> + * @tot_len:	Payload length
> + * @proto:	Protocol number
> + * @saddr:	Source address
> + * @daddr:	Destination address
> + * @proto:	proto Protocol number
> + * Returns:	Partial checksum of the IPv4 header
> + */
> +uint32_t proto_ipv4_header_psum(uint16_t tot_len, uint8_t protocol,
> +				uint32_t saddr, uint32_t daddr)
> +{
> +	uint32_t psum = htons(protocol);
> +
> +	psum += (saddr >> 16) & 0xffff;
> +	psum += saddr & 0xffff;
> +	psum += (daddr >> 16) & 0xffff;
> +	psum += daddr & 0xffff;
> +	psum += htons(ntohs(tot_len) - 20);
> +
> +	return psum;
> +}
> +
>  /**
>   * csum_udp4() - Calculate and set checksum for a UDP over IPv4 packet
>   * @udp4hr:	UDP header, initialised apart from checksum
> @@ -150,14 +174,10 @@ void csum_udp4(struct udphdr *udp4hr,
>  	udp4hr->check = 0;
>  
>  	if (UDP4_REAL_CHECKSUMS) {
> -		/* UNTESTED: if we did want real UDPv4 checksums, this
> -		 * is roughly what we'd need */
> -		uint32_t psum = csum_fold(saddr.s_addr)
> -			+ csum_fold(daddr.s_addr)
> -			+ htons(len + sizeof(*udp4hr))
> -			+ htons(IPPROTO_UDP);
> -		/* Add in partial checksum for the UDP header alone */
> -		psum += sum_16b(udp4hr, sizeof(*udp4hr));
> +		uint32_t psum = proto_ipv4_header_psum(len, IPPROTO_UDP,
> +						       saddr.s_addr,
> +						       daddr.s_addr);
> +		psum = csum_unfolded(udp4hr, sizeof(struct udphdr), psum);
>  		udp4hr->check = csum(payload, len, psum);
>  	}
>  }
> @@ -180,6 +200,26 @@ void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t len)
>  	icmp4hr->checksum = csum(payload, len, psum);
>  }
>  
> +/**
> + * proto_ipv6_header_psum() - Calculates the partial checksum of an
> + * 			      IPv6 header for UDP or TCP
> + * @payload_len:	Payload length
> + * @proto:		Protocol number
> + * @saddr:		Source address
> + * @daddr:		Destination address
> + * Returns:	Partial checksum of the IPv6 header
> + */
> +uint32_t proto_ipv6_header_psum(uint16_t payload_len, uint8_t protocol,
> +				struct in6_addr saddr, struct in6_addr daddr)

Hrm, this is passing 2 16-byte IPv6 addresses by value, which might
not be what we want.

> +{
> +	uint32_t sum = htons(protocol) + payload_len;

Uh.. doesn't that need to be htons(payload_len + sizeof(struct
ipv6hdr)) rather than simply payload_len?

> +
> +	sum += sum_16b(&saddr, sizeof(saddr));
> +	sum += sum_16b(&daddr, sizeof(daddr));
> +
> +	return sum;
> +}
> +
>  /**
>   * csum_udp6() - Calculate and set checksum for a UDP over IPv6 packet
>   * @udp6hr:	UDP header, initialised apart from checksum
> @@ -190,14 +230,11 @@ void csum_udp6(struct udphdr *udp6hr,
>  	       const struct in6_addr *saddr, const struct in6_addr *daddr,
>  	       const void *payload, size_t len)
>  {
> -	/* Partial checksum for the pseudo-IPv6 header */
> -	uint32_t psum = sum_16b(saddr, sizeof(*saddr)) +
> -		        sum_16b(daddr, sizeof(*daddr)) +
> -		        htons(len + sizeof(*udp6hr)) + htons(IPPROTO_UDP);
> -
> +	uint32_t psum = proto_ipv6_header_psum(len, IPPROTO_UDP,
> +					       *saddr, *daddr);
>  	udp6hr->check = 0;
> -	/* Add in partial checksum for the UDP header alone */
> -	psum += sum_16b(udp6hr, sizeof(*udp6hr));
> +
> +	psum = csum_unfolded(udp6hr, sizeof(struct udphdr), psum);
>  	udp6hr->check = csum(payload, len, psum);
>  }
>  
> diff --git a/checksum.h b/checksum.h
> index 92db73612b6e..b2b5b8e8b77e 100644
> --- a/checksum.h
> +++ b/checksum.h
> @@ -15,10 +15,14 @@ uint16_t csum_fold(uint32_t sum);
>  uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init);
>  uint16_t csum_ip4_header(uint16_t tot_len, uint8_t protocol,
>  			 uint32_t saddr, uint32_t daddr);
> +uint32_t proto_ipv4_header_psum(uint16_t tot_len, uint8_t protocol,
> +				uint32_t saddr, uint32_t daddr);
>  void csum_udp4(struct udphdr *udp4hr,
>  	       struct in_addr saddr, struct in_addr daddr,
>  	       const void *payload, size_t len);
>  void csum_icmp4(struct icmphdr *ih, const void *payload, size_t len);
> +uint32_t proto_ipv6_header_psum(uint16_t payload_len, uint8_t protocol,
> +				struct in6_addr saddr, struct in6_addr daddr);
>  void csum_udp6(struct udphdr *udp6hr,
>  	       const struct in6_addr *saddr, const struct in6_addr *daddr,
>  	       const void *payload, size_t len);
> diff --git a/tcp.c b/tcp.c
> index 8887656d3ee8..8ee252131504 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -938,39 +938,29 @@ 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 void 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 = (struct tcphdr *)(iph + 1);
> +	uint16_t tlen = ntohs(iph->tot_len) - 20;
> +	uint32_t sum = proto_ipv4_header_psum(iph->tot_len, IPPROTO_TCP,
> +					      iph->saddr, iph->daddr);
>  
> -	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);
> +	th->check = 0;
> +	th->check = 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 void 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 = (struct tcphdr *)(ip6h + 1);
> +	uint32_t sum = proto_ipv6_header_psum(ip6h->payload_len, IPPROTO_TCP,
> +					      ip6h->saddr, ip6h->daddr);
>  
> -	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;
> +	th->check = 0;
> +	th->check = csum(th, ntohs(ip6h->payload_len), sum);
>  }
>  
>  /**
> @@ -1382,7 +1372,7 @@ do {									\
>  
>  		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
>  
> -		tcp_update_check_tcp4(b);
> +		tcp_update_check_tcp4(&b->iph);
>  
>  		tlen = tap_iov_len(c, &b->taph, ip_len);
>  	} else {
> @@ -1401,7 +1391,11 @@ do {									\
>  
>  		SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq);
>  
> -		tcp_update_check_tcp6(b);
> +		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 cd34f659210b..e123b35a955c 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -670,10 +670,12 @@ 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 = 0;
> +	b->uh.check = csum(&b->uh, ntohs(b->ip6h.payload_len),
> +			   proto_ipv6_header_psum(b->ip6h.payload_len,
> +						  IPPROTO_UDP,
> +						  b->ip6h.saddr,
> +						  b->ip6h.daddr));
>  	b->ip6h.version = 6;
>  	b->ip6h.nexthdr = IPPROTO_UDP;
>  	b->ip6h.hop_limit = 255;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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