[PATCH v5 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 that exceed available buffer space are skipped
with a rate-limited warning.

Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v5:
  - Replaced warn() with warn_ratelimit(now, ...)

v4:
  - warn() instead of debug() when options don't fit in the reply.
  - doc comment for dhcpv6_user_opts_fill() updated.

v3:
  - rename dhcpv6_custom_opts_fill() to dhcpv6_user_opts_fill().
  - Iterate directly over the pre-parsed binary dhcpv6_user_opts[]
    array instead of re-parsing string values at reply time.

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 +++++++++++++++++++++++++++++++++++++++++++-
 dhcpv6.h |  3 ++-
 tap.c    |  2 +-
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/dhcpv6.c b/dhcpv6.c
index a98f1a9c..9bafa99e 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -891,17 +891,58 @@ static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data,
 	return offset + sizeof(struct opt_hdr) + opt_len;
 }
 
+/**
+ * dhcpv6_user_opts_fill() - Append user-specified options to reply
+ * @buf:	Response message buffer
+ * @offset:	Current offset in buffer
+ * @now:	Current timestamp
+ *
+ * Return: offset after appended user options
+ */
+static size_t dhcpv6_user_opts_fill(char *buf, size_t offset,
+				    const struct timespec *now)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(dhcpv6_user_opts); i++) {
+		int vlen = dhcpv6_user_opts[i].len;
+		struct opt_hdr *hdr;
+
+		if (!vlen)
+			continue;
+
+		if (offset + sizeof(struct opt_hdr) + vlen > OPT_MAX_SIZE) {
+			warn_ratelimit(now,
+				       "DHCPv6: option %u doesn't fit, skipping",
+				       i);
+			continue;
+		}
+
+		hdr = (struct opt_hdr *)(buf + offset);
+		hdr->t = htons(i);
+		hdr->l = htons(vlen);
+		offset += sizeof(struct opt_hdr);
+
+		memcpy(buf + offset, dhcpv6_user_opts[i].val, vlen);
+		offset += vlen;
+	}
+
+	return offset;
+}
+
 /**
  * dhcpv6() - Check if this is a DHCPv6 message, reply as needed
  * @c:		Execution context
  * @data:	Single packet starting from UDP header
  * @saddr:	Source IPv6 address of original message
  * @daddr:	Destination IPv6 address of original message
+ * @now:	Current timestamp
  *
  * Return: 0 if it's not a DHCPv6 message, 1 if handled, -1 on failure
  */
 int dhcpv6(struct ctx *c, struct iov_tail *data,
-	   const struct in6_addr *saddr, const struct in6_addr *daddr)
+	   const struct in6_addr *saddr, const struct in6_addr *daddr,
+	   const struct timespec *now)
 {
 	const struct opt_server_id *server_id = NULL;
 	const struct opt_hdr *client_id = NULL;
@@ -1029,6 +1070,7 @@ 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_user_opts_fill((char *)&resp, n, now);
 
 	resp.hdr.xid = mh->xid;
 
diff --git a/dhcpv6.h b/dhcpv6.h
index 6cefd15b..00cf51af 100644
--- a/dhcpv6.h
+++ b/dhcpv6.h
@@ -7,7 +7,8 @@
 #define DHCPV6_H
 
 int dhcpv6(struct ctx *c, struct iov_tail *data,
-	   const struct in6_addr *saddr, const struct in6_addr *daddr);
+	   const struct in6_addr *saddr, const struct in6_addr *daddr,
+	   const struct timespec *now);
 void dhcpv6_init(const struct ctx *c);
 void dhcpv6_set_opt(uint16_t code, const char *val_str);
 const char *dhcpv6_opt_to_str(uint16_t code, char *buf, size_t buf_len,
diff --git a/tap.c b/tap.c
index dfa66c71..0a9938de 100644
--- a/tap.c
+++ b/tap.c
@@ -1041,7 +1041,7 @@ resume:
 		if (proto == IPPROTO_UDP) {
 			struct iov_tail uh_data = data;
 
-			if (dhcpv6(c, &uh_data, saddr, daddr))
+			if (dhcpv6(c, &uh_data, saddr, daddr, now))
 				continue;
 		}
 
-- 
2.55.0