udp: Rework offender address handling in udp_sock_recverr()

Make a number of changes to udp_sock_recverr() to improve the robustness
of how we handle addresses.

 * Get the "offender" address (source of the ICMP packet) using the
   SO_EE_OFFENDER() macro, reducing assumptions about structure layout.
 * Parse the offender sockaddr using inany_from_sockaddr()
 * Check explicitly that the source and destination pifs are what we
   expect.  Previously we checked something that was probably equivalent
   in practice, but isn't strictly speaking what we require for the rest
   of the code.
 * Verify that for an ICMPv4 error we also have an IPv4 source/offender
   and destination/endpoint address
 * Verify that for an ICMPv6 error we have an IPv6 endpoint
 * Improve debug reporting of any failures

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 48 insertions, 21 deletions

diff --git a/udp.c b/udp.c
index 57769d0..d09b3eb 100644
--- a/udp.c
+++ b/udp.c
@@ -159,6 +159,12 @@ udp_meta[UDP_MAX_FRAMES];
 	MAX(CMSG_SPACE(sizeof(struct in_pktinfo)),	\
 	    CMSG_SPACE(sizeof(struct in6_pktinfo)))
 
+#define RECVERR_SPACE							\
+	MAX(CMSG_SPACE(sizeof(struct sock_extended_err) +		\
+		       sizeof(struct sockaddr_in)),			\
+	    CMSG_SPACE(sizeof(struct sock_extended_err) +		\
+		       sizeof(struct sockaddr_in6)))
+
 /**
  * enum udp_iov_idx - Indices for the buffers making up a single UDP frame
  * @UDP_IOV_TAP         tap specific header
@@ -516,12 +522,8 @@ static int udp_pktinfo(struct msghdr *msg, union inany_addr *dst)
 static int udp_sock_recverr(const struct ctx *c, int s, flow_sidx_t sidx,
 			    uint8_t pif, in_port_t port)
 {
-	struct errhdr {
-		struct sock_extended_err ee;
-		union sockaddr_inany saddr;
-	};
-	char buf[PKTINFO_SPACE + CMSG_SPACE(sizeof(struct errhdr))];
-	const struct errhdr *eh = NULL;
+	char buf[PKTINFO_SPACE + RECVERR_SPACE];
+	const struct sock_extended_err *ee;
 	char data[ICMP6_MAX_DLEN];
 	struct cmsghdr *hdr;
 	struct iovec iov = {
@@ -538,7 +540,13 @@ static int udp_sock_recverr(const struct ctx *c, int s, flow_sidx_t sidx,
 		.msg_controllen = sizeof(buf),
 	};
 	const struct flowside *toside;
-	flow_sidx_t tosidx;
+	char astr[INANY_ADDRSTRLEN];
+	char sastr[SOCKADDR_STRLEN];
+	union inany_addr offender;
+	const struct in_addr *o4;
+	in_port_t offender_port;
+	struct udp_flow *uflow;
+	uint8_t topif;
 	size_t dlen;
 	ssize_t rc;
 
@@ -569,10 +577,10 @@ static int udp_sock_recverr(const struct ctx *c, int s, flow_sidx_t sidx,
 		return -1;
 	}
 
-	eh = (const struct errhdr *)CMSG_DATA(hdr);
+	ee = (const struct sock_extended_err *)CMSG_DATA(hdr);
 
 	debug("%s error on UDP socket %i: %s",
-	      str_ee_origin(&eh->ee), s, strerror_(eh->ee.ee_errno));
+	      str_ee_origin(ee), s, strerror_(ee->ee_errno));
 
 	if (!flow_sidx_valid(sidx)) {
 		/* No hint from the socket, determine flow from addresses */
@@ -588,25 +596,44 @@ static int udp_sock_recverr(const struct ctx *c, int s, flow_sidx_t sidx,
 			debug("Ignoring UDP error without flow");
 			return 1;
 		}
+	} else {
+		pif = pif_at_sidx(sidx);
 	}
 
-	tosidx = flow_sidx_opposite(sidx);
-	toside = flowside_at_sidx(tosidx);
+	uflow = udp_at_sidx(sidx);
+	ASSERT(uflow);
+	toside = &uflow->f.side[!sidx.sidei];
+	topif = uflow->f.pif[!sidx.sidei];
 	dlen = rc;
 
-	if (pif_is_socket(pif_at_sidx(tosidx))) {
-		/* XXX Is there any way to propagate ICMPs from socket to
-		 * socket? */
-	} else if (hdr->cmsg_level == IPPROTO_IP) {
+	if (inany_from_sockaddr(&offender, &offender_port,
+				SO_EE_OFFENDER(ee)) < 0)
+		goto fail;
+
+	if (pif != PIF_HOST || topif != PIF_TAP)
+		/* XXX Can we support any other cases? */
+		goto fail;
+
+	if (hdr->cmsg_level == IPPROTO_IP &&
+	    (o4 = inany_v4(&offender)) && inany_v4(&toside->eaddr)) {
 		dlen = MIN(dlen, ICMP4_MAX_DLEN);
-		udp_send_tap_icmp4(c, &eh->ee, toside,
-				   eh->saddr.sa4.sin_addr, data, dlen);
-	} else if (hdr->cmsg_level == IPPROTO_IPV6) {
-		udp_send_tap_icmp6(c, &eh->ee, toside,
-				   &eh->saddr.sa6.sin6_addr, data,
-				   dlen, sidx.flowi);
+		udp_send_tap_icmp4(c, ee, toside, *o4, data, dlen);
+		return 1;
 	}
 
+	if (hdr->cmsg_level == IPPROTO_IPV6 && !inany_v4(&toside->eaddr)) {
+		udp_send_tap_icmp6(c, ee, toside, &offender.a6, data, dlen,
+				   FLOW_IDX(uflow));
+		return 1;
+	}
+
+fail:
+	flow_dbg(uflow, "Can't propagate %s error from %s %s to %s %s",
+		 str_ee_origin(ee),
+		 pif_name(pif),
+		 sockaddr_ntop(SO_EE_OFFENDER(ee), sastr, sizeof(sastr)),
+		 pif_name(topif),
+		 inany_ntop(&toside->eaddr, astr, sizeof(astr)));
 	return 1;
 }