[PATCH v2 2/2] udp: support traceroute with udp

[Jon Maloy <jmaloy@redhat.com>]

Now that ICMP pass-through from socket-to-tap and TTL/hop limit based
outgoing flow separation is in place, it is easy to support UDP based
traceroute functionality in direction tap-to-socket.

We fix that in this commit.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
---
v2: Using ancillary data instead  of setsockopt to transfer outgoing
    TTL.
---
 udp.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/udp.c b/udp.c
index 8a2c593..7361ffa 100644
--- a/udp.c
+++ b/udp.c
@@ -861,6 +861,7 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 		    uint8_t ttl, const struct pool *p, int idx,
 		    const struct timespec *now)
 {
+	char ancillary[CMSG_SPACE(sizeof(int))];
 	const struct flowside *toside;
 	struct mmsghdr mm[UIO_MAXIOV];
 	union sockaddr_inany to_sa;
@@ -868,6 +869,8 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 	const struct udphdr *uh;
 	struct udp_flow *uflow;
 	int i, s, count = 0;
+	char *control = NULL;
+	int control_len = 0;
 	flow_sidx_t tosidx;
 	in_port_t src, dst;
 	uint8_t topif;
@@ -914,6 +917,22 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 
 	pif_sockaddr(c, &to_sa, &sl, topif, &toside->eaddr, toside->eport);
 
+	if (ttl != DEFAULT_TTL) {
+		struct cmsghdr *cmsg = (void *) ancillary;
+
+		if (af == AF_INET) {
+			cmsg->cmsg_level = IPPROTO_IP;
+			cmsg->cmsg_type = IP_TTL;
+		} else {
+			cmsg->cmsg_level = IPPROTO_IPV6;
+			cmsg->cmsg_type = IPV6_HOPLIMIT;
+		}
+		cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+		*((int *) CMSG_DATA(cmsg)) = ttl;
+		control = ancillary;
+		control_len = sizeof(ancillary);
+	}
+
 	for (i = 0; i < (int)p->count - idx; i++) {
 		struct udphdr *uh_send;
 		size_t len;
@@ -936,8 +955,8 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 			mm[i].msg_hdr.msg_iovlen = 0;
 		}
 
-		mm[i].msg_hdr.msg_control = NULL;
-		mm[i].msg_hdr.msg_controllen = 0;
+		mm[i].msg_hdr.msg_control = control;
+		mm[i].msg_hdr.msg_controllen = control_len;
 		mm[i].msg_hdr.msg_flags = 0;
 
 		count++;
-- 
@@ -861,6 +861,7 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 		    uint8_t ttl, const struct pool *p, int idx,
 		    const struct timespec *now)
 {
+	char ancillary[CMSG_SPACE(sizeof(int))];
 	const struct flowside *toside;
 	struct mmsghdr mm[UIO_MAXIOV];
 	union sockaddr_inany to_sa;
@@ -868,6 +869,8 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 	const struct udphdr *uh;
 	struct udp_flow *uflow;
 	int i, s, count = 0;
+	char *control = NULL;
+	int control_len = 0;
 	flow_sidx_t tosidx;
 	in_port_t src, dst;
 	uint8_t topif;
@@ -914,6 +917,22 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 
 	pif_sockaddr(c, &to_sa, &sl, topif, &toside->eaddr, toside->eport);
 
+	if (ttl != DEFAULT_TTL) {
+		struct cmsghdr *cmsg = (void *) ancillary;
+
+		if (af == AF_INET) {
+			cmsg->cmsg_level = IPPROTO_IP;
+			cmsg->cmsg_type = IP_TTL;
+		} else {
+			cmsg->cmsg_level = IPPROTO_IPV6;
+			cmsg->cmsg_type = IPV6_HOPLIMIT;
+		}
+		cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+		*((int *) CMSG_DATA(cmsg)) = ttl;
+		control = ancillary;
+		control_len = sizeof(ancillary);
+	}
+
 	for (i = 0; i < (int)p->count - idx; i++) {
 		struct udphdr *uh_send;
 		size_t len;
@@ -936,8 +955,8 @@ int udp_tap_handler(const struct ctx *c, uint8_t pif,
 			mm[i].msg_hdr.msg_iovlen = 0;
 		}
 
-		mm[i].msg_hdr.msg_control = NULL;
-		mm[i].msg_hdr.msg_controllen = 0;
+		mm[i].msg_hdr.msg_control = control;
+		mm[i].msg_hdr.msg_controllen = control_len;
 		mm[i].msg_hdr.msg_flags = 0;
 
 		count++;
-- 
2.48.1