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Add csum_icmp6() helper for calculating ICMPv6 checksums

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At least two places in passt calculate ICMPv6 checksums, ndp() and
tap_ip_send().  Add a helper to handle this calculation in both places.
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 ICMPv6 header and payload to
be in separate buffers, although we don't use this yet.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2022-10-19 11:43:44 +11:00 committed by Stefano Brivio
parent b3f359167b
commit 7abd2b0d72
4 changed files with 33 additions and 8 deletions
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25
checksum.c
View file

@ -52,6 +52,8 @@
#include <stddef.h>
#include <stdint.h>
#include <linux/icmpv6.h>
/**
* sum_16b() - Calculate sum of 16-bit words
* @buf: Input buffer
@ -105,6 +107,29 @@ uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
return (uint16_t)~csum_fold(sum_16b(buf, len) + init);
}
/**
* csum_icmp6() - Calculate and set checksum for an ICMPv6 packet
* @icmp6hr: ICMPv6 header, initialised apart from checksum
* @saddr: IPv6 source address
* @daddr: IPv6 destination address
* @payload: ICMP packet payload
* @len: Length of @payload (not including ICMPv6 header)
*/
void csum_icmp6(struct icmp6hdr *icmp6hr,
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(*icmp6hr)) + htons(IPPROTO_ICMPV6);
icmp6hr->icmp6_cksum = 0;
/* Add in partial checksum for the ICMPv6 header alone */
psum += sum_16b(icmp6hr, sizeof(*icmp6hr));
icmp6hr->icmp6_cksum = csum_unaligned(payload, len, psum);
}
/**
* csum_tcp4() - Calculate TCP checksum for IPv4 and set in place
* @iph: Packet buffer, IP header

5
checksum.h
View file

@ -6,9 +6,14 @@
#ifndef CHECKSUM_H
#define CHECKSUM_H
struct icmp6hdr;
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_icmp6(struct icmp6hdr *icmp6hr,
const struct in6_addr *saddr, const struct in6_addr *daddr,
const void *payload, size_t len);
void csum_tcp4(struct iphdr *iph);
uint16_t csum(const void *buf, size_t len, uint32_t init);

5
ndp.c
View file

@ -189,10 +189,7 @@ dns_done:
ip6hr->saddr = c->ip6.addr_ll;
ip6hr->payload_len = htons(sizeof(*ihr) + len);
ip6hr->hop_limit = IPPROTO_ICMPV6;
ihr->icmp6_cksum = 0;
ihr->icmp6_cksum = csum_unaligned(ip6hr, sizeof(*ip6hr) +
sizeof(*ihr) + len, 0);
csum_icmp6(ihr, &ip6hr->saddr, &ip6hr->daddr, ihr + 1, len);
ip6hr->version = 6;
ip6hr->nexthdr = IPPROTO_ICMPV6;

6
tap.c
View file

@ -191,10 +191,8 @@ void tap_ip_send(const struct ctx *c, const struct in6_addr *src, uint8_t proto,
} else if (proto == IPPROTO_ICMPV6) {
struct icmp6hdr *ih = (struct icmp6hdr *)(ip6h + 1);
ih->icmp6_cksum = 0;
ih->icmp6_cksum = csum_unaligned(ip6h,
len + sizeof(*ip6h),
0);
csum_icmp6(ih, &ip6h->saddr, &ip6h->daddr,
ih + 1, len - sizeof(*ih));
}
ip6h->version = 6;
ip6h->nexthdr = proto;