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udp: Add udp_pktinfo() helper

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Currently we open code parsing the control message for IP_PKTINFO in
udp_peek_addr().  We have an upcoming case where we want to parse PKTINFO
in another place, so split this out into a helper function.

While we're there, make the parsing a bit more robust: scan all cmsgs to
look for the one we want, rather than assuming there's only one.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: udp_pktinfo(): Fix typo in comment and change err() to debug()]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2025-04-15 17:16:22 +10:00 • committed by Stefano Brivio
parent 04984578b0
commit f107a86cc0
1 changed files with 36 additions and 16 deletions

52
udp.c
View file

@ -464,6 +464,41 @@ static void udp_send_tap_icmp6(const struct ctx *c,
tap_icmp6_send(c, saddr, eaddr, &msg, msglen); tap_icmp6_send(c, saddr, eaddr, &msg, msglen);
} }
/**
* udp_pktinfo() - Retrieve packet destination address from cmsg
* @msg: msghdr into which message has been received
* @dst: (Local) destination address of message in @mh (output)
*
* Return: 0 on success, -1 if the information was missing (@dst is set to
* inany_any6).
*/
static int udp_pktinfo(struct msghdr *msg, union inany_addr *dst)
{
struct cmsghdr *hdr;
for (hdr = CMSG_FIRSTHDR(msg); hdr; hdr = CMSG_NXTHDR(msg, hdr)) {
if (hdr->cmsg_level == IPPROTO_IP &&
hdr->cmsg_type == IP_PKTINFO) {
const struct in_pktinfo *i4 = (void *)CMSG_DATA(hdr);
*dst = inany_from_v4(i4->ipi_addr);
return 0;
}
if (hdr->cmsg_level == IPPROTO_IPV6 &&
hdr->cmsg_type == IPV6_PKTINFO) {
const struct in6_pktinfo *i6 = (void *)CMSG_DATA(hdr);
dst->a6 = i6->ipi6_addr;
return 0;
}
}
debug("Missing PKTINFO cmsg on datagram");
*dst = inany_any6;
return -1;
}
/** /**
* udp_sock_recverr() - Receive and clear an error from a socket * udp_sock_recverr() - Receive and clear an error from a socket
* @c: Execution context * @c: Execution context
@ -607,7 +642,6 @@ static int udp_peek_addr(int s, union sockaddr_inany *src,
union inany_addr *dst) union inany_addr *dst)
{ {
char sastr[SOCKADDR_STRLEN], dstr[INANY_ADDRSTRLEN]; char sastr[SOCKADDR_STRLEN], dstr[INANY_ADDRSTRLEN];
const struct cmsghdr *hdr;
char cmsg[PKTINFO_SPACE]; char cmsg[PKTINFO_SPACE];
struct msghdr msg = { struct msghdr msg = {
.msg_name = src, .msg_name = src,
@ -624,21 +658,7 @@ static int udp_peek_addr(int s, union sockaddr_inany *src,
return -errno; return -errno;
} }
hdr = CMSG_FIRSTHDR(&msg); udp_pktinfo(&msg, dst);
if (hdr && hdr->cmsg_level == IPPROTO_IP &&
hdr->cmsg_type == IP_PKTINFO) {
const struct in_pktinfo *info4 = (void *)CMSG_DATA(hdr);
*dst = inany_from_v4(info4->ipi_addr);
} else if (hdr && hdr->cmsg_level == IPPROTO_IPV6 &&
hdr->cmsg_type == IPV6_PKTINFO) {
const struct in6_pktinfo *info6 = (void *)CMSG_DATA(hdr);
dst->a6 = info6->ipi6_addr;
} else {
debug("Unexpected cmsg on UDP datagram");
*dst = inany_any6;
}
trace("Peeked UDP datagram: %s -> %s", trace("Peeked UDP datagram: %s -> %s",
sockaddr_ntop(src, sastr, sizeof(sastr)), sockaddr_ntop(src, sastr, sizeof(sastr)),