[PATCH v2 2/2] dhcpv6: Inject custom options into DHCPv6 replies

[Anshu Kumari <anskuma@redhat.com>]

Append user-specified options from --dhcpv6-opt to DHCPv6 reply
messages.  Options are parsed from the stored string value at reply
time using dhcpv6_opt_parse(), and skipped with a debug message if
they exceed the available space.

Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v2:
  - Updated dhcpv6_custom_opts_fill() to parse str at reply time
    using dhcpv6_opt_parse() instead of copying cached val/len.
---
 dhcpv6.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/dhcpv6.c b/dhcpv6.c
index 1e1dd0d..6b1e90b 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -748,6 +748,49 @@ 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->dhcpv6_opts_count; i++) {
+		uint16_t code = c->dhcpv6_opts[i].code;
+		struct opt_hdr *hdr;
+		uint8_t val[255];
+		int vlen;
+
+		vlen = dhcpv6_opt_parse(code, c->dhcpv6_opts[i].str,
+					val, sizeof(val));
+		if (vlen < 0)
+			continue;
+
+		if ((size_t)offset + sizeof(struct opt_hdr) + vlen >
+		    OPT_MAX_SIZE) {
+			debug("DHCPv6: custom option %u doesn't fit,"
+			      " skipping", code);
+			continue;
+		}
+
+		hdr = (struct opt_hdr *)(buf + offset);
+		hdr->t = htons(code);
+		hdr->l = htons(vlen);
+		offset += sizeof(struct opt_hdr);
+
+		memcpy(buf + offset, val, vlen);
+		offset += vlen;
+	}
+
+	return offset;
+}
+
 /**
  * dhcpv6() - Check if this is a DHCPv6 message, reply as needed
  * @c:		Execution context
@@ -886,6 +929,7 @@ 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