[PATCH 3/3] dhcpv6: Inject custom options into DHCPv6 replies

[Anshu Kumari <anskuma@redhat.com>]

Add dhcpv6_custom_opts_fill() which appends user-specified custom
options to DHCPv6 response packets, and call it from the main dhcpv6()
handler after the built-in DNS and FQDN options.

Each custom option is written with its DHCPv6 option header (code +
length) followed by the binary-encoded value from dhcpv6_opt_parse().
Options that would exceed the IPv6 minimum MTU are skipped with a
debug message.

Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
 dhcpv6.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/dhcpv6.c b/dhcpv6.c
index 85e2926..590c40d 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -798,6 +798,41 @@ static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data,
 	return offset + sizeof(struct opt_hdr) + opt_len;
 }
 
+/**
+ * dhcpv6_custom_opts_fill() - Append user-specified custom options to reply
+ * @c:		Execution context
+ * @buf:	Response message buffer
+ * @offset:	Current offset in buffer
+ *
+ * Return: updated offset after appending custom options
+ */
+static size_t dhcpv6_custom_opts_fill(const struct ctx *c,
+				      char *buf, int offset)
+{
+	int i;
+
+	for (i = 0; i < c->custom_v6opts_count; i++) {
+		struct opt_hdr *hdr;
+		uint16_t len = c->custom_v6opts[i].len;
+
+		if ((size_t)offset + sizeof(struct opt_hdr) + len > OPT_MAX_SIZE) {
+			debug("DHCPv6: custom option %u doesn't fit, skipping",
+			      c->custom_v6opts[i].code);
+			continue;
+		}
+
+		hdr = (struct opt_hdr *)(buf + offset);
+		hdr->t = htons(c->custom_v6opts[i].code);
+		hdr->l = htons(len);
+		offset += sizeof(struct opt_hdr);
+
+		memcpy(buf + offset, c->custom_v6opts[i].val, len);
+		offset += len;
+	}
+
+	return offset;
+}
+
 /**
  * dhcpv6() - Check if this is a DHCPv6 message, reply as needed
  * @c:		Execution context
@@ -936,6 +971,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data,
 	    sizeof(struct opt_hdr) + ntohs(client_id->l);
 	n = dhcpv6_dns_fill(c, (char *)&resp, n);
 	n = dhcpv6_client_fqdn_fill(data, c, (char *)&resp, n);
+	n = dhcpv6_custom_opts_fill(c, (char *)&resp, n);
 
 	resp.hdr.xid = mh->xid;
 
-- 
2.54.0