Re: [PATCH 03/14] Add csum_udp6() helper for calculating UDP over IPv6 checksums

On Mon, 17 Oct 2022 19:57:56 +1100
David Gibson <david(a)gibson.dropbear.id.au> wrote:

...
  Add a helper for calculating UDP checksums when used
over IPv6
 For future flexibility, the new helper takes parameters for the fields in
 the IPv6 pseudo-header, so an IPv6 header or pseudo-header doesn't need to
 be explicitly constructed.  It also allows the UDP header and payload to
 be in separate buffers, although we don't use this yet.
 
 Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
 ---
  checksum.c | 23 +++++++++++++++++++++++
  checksum.h |  5 +++++
  tap.c      |  5 ++---
  3 files changed, 30 insertions(+), 3 deletions(-)
 
 diff --git a/checksum.c b/checksum.c
 index c8b6b42..0849fb1 100644
 --- a/checksum.c
 +++ b/checksum.c
 @@ -52,6 +52,7 @@
  #include <stddef.h>
  #include <stdint.h>
  
 +#include <linux/udp.h>
  #include <linux/icmp.h>
  #include <linux/icmpv6.h>
  
 @@ -122,6 +123,28 @@ void csum_icmp4(struct icmphdr *icmp4hr, const void *payload, size_t
len)
  	icmp4hr->checksum = csum_unaligned(payload, len, hrsum);
  }
  
 +/**
 + * csum_udp6() - Calculate checksum for a UDP over IPv6 packet 
Calculate and set.

...
  + * @udp6hr:	UDP header, initialized apart from
checksum 
-ised.

...
  + * @payload:	UDP packet payload
 + * @len:	Length of @payload (not including UDP header)
 + */
 +void csum_udp6(struct udphdr *udp6hr,
 +	       const struct in6_addr *saddr,
 +	       const struct in6_addr *daddr, 
You could use some horizontal space.

...
  +	       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); 
Alignment:

	uint32_t psum = sum_16b(saddr, sizeof(*saddr)) +
			sum_16b(daddr, sizeof(*daddr)) +
			htons(len + sizeof(*udp6hr))   + htons(IPPROTO_UDP);

...
  +	udp6hr->check = 0;
 +	/* Add in partial checksum for the UDP header alone */
 +	psum += sum_16b(udp6hr, sizeof(*udp6hr));
 +	udp6hr->check = csum_unaligned(payload, len, psum);
 +}
 +
  /**
   * csum_icmp6() - Calculate checksum for an ICMPv6 packet
   * @icmp6hr:	ICMPv6 header, initialized apart from checksum
 diff --git a/checksum.h b/checksum.h
 index ff95cf9..1b9f48e 100644
 --- a/checksum.h
 +++ b/checksum.h
 @@ -6,6 +6,7 @@
  #ifndef CHECKSUM_H
  #define CHECKSUM_H
  
 +struct udphdr;
  struct icmphdr;
  struct icmp6hdr;
  
 @@ -13,6 +14,10 @@ uint32_t sum_16b(const void *buf, size_t len);
  uint16_t csum_fold(uint32_t sum);
  uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init);
  void csum_icmp4(struct icmphdr *ih, const void *payload, size_t len);
 +void csum_udp6(struct udphdr *udp6hr,
 +	       const struct in6_addr *saddr,
 +	       const struct in6_addr *daddr,
 +	       const void *payload, size_t len); 
Use some horizontal space.

...
   void csum_icmp6(struct icmp6hdr *ih,
  		const struct in6_addr *saddr,
  		const struct in6_addr *daddr,
 diff --git a/tap.c b/tap.c
 index f082901..9c197cb 100644
 --- a/tap.c
 +++ b/tap.c
 @@ -183,9 +183,8 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src,
uint8_t proto,
  		} else if (proto == IPPROTO_UDP) {
  			struct udphdr *uh = (struct udphdr *)(ip6h + 1);
  
 -			uh->check = 0;
 -			uh->check = csum_unaligned(ip6h, len + sizeof(*ip6h),
 -						   0);
 +			csum_udp6(uh, &ip6h->saddr, &ip6h->daddr,
 +				  uh + 1, len - sizeof(*uh));
  		} else if (proto == IPPROTO_ICMPV6) {
  			struct icmp6hdr *ih = (struct icmp6hdr *)(ip6h + 1);
   
-- 
Stefano