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tap: Fill the IPv6 flow label field to represent flow association

Browse source 
This isn't optional: TCP streams must carry a unique, hard-to-guess,
non-zero label for each direction. Linux, probably among others,
will otherwise refuse to associate packets in a given stream to the
same connection.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2021-07-26 07:30:57 +02:00
parent 17765f8de0
commit 16b08367a5
5 changed files with 25 additions and 10 deletions

18
tap.c
View file

@ -91,9 +91,10 @@ int tap_send(struct ctx *c, void *data, size_t len, int vnet_pre)
* @proto: L4 protocol number
* @in: Payload
* @len: L4 payload length
* @flow: Flow label for TCP over IPv6
*/
void tap_ip_send(struct ctx *c, struct in6_addr *src, uint8_t proto,
char *in, size_t len)
char *in, size_t len, uint32_t flow)
{
char buf[USHRT_MAX];
char *pkt = buf + 4;
@ -161,21 +162,30 @@ void tap_ip_send(struct ctx *c, struct in6_addr *src, uint8_t proto,
struct tcphdr *th = (struct tcphdr *)(ip6h + 1);
th->check = 0;
th->check = csum_ip4(ip6h, len + sizeof(*ip6h));
th->check = csum_unaligned(ip6h, len + sizeof(*ip6h),
0);
} else if (proto == IPPROTO_UDP) {
struct udphdr *uh = (struct udphdr *)(ip6h + 1);
uh->check = 0;
uh->check = csum_ip4(ip6h, len + sizeof(*ip6h));
uh->check = csum_unaligned(ip6h, len + sizeof(*ip6h),
0);
} else if (proto == IPPROTO_ICMPV6) {
struct icmp6hdr *ih = (struct icmp6hdr *)(ip6h + 1);
ih->icmp6_cksum = 0;
ih->icmp6_cksum = csum_ip4(ip6h, len + sizeof(*ip6h));
ih->icmp6_cksum = csum_unaligned(ip6h,
len + sizeof(*ip6h),
0);
}
ip6h->version = 6;
ip6h->nexthdr = proto;
ip6h->hop_limit = 255;
if (flow) {
ip6h->flow_lbl[0] = (flow >> 16) & 0xf;
ip6h->flow_lbl[1] = (flow >> 8) & 0xff;
ip6h->flow_lbl[2] = (flow >> 0) & 0xff;
}
tap_send(c, buf, len + sizeof(*ip6h) + sizeof(*eh), 1);
}