vrrpd: read and validate vrrp advertisements

* Validate IPvX headers and packet contents
* Remove filter of non-255 TTL IPv4 packets; better to receive, log and
  drop them ourselves
* Set outgoing packet TTL / hop limit to 255
* Use existing sockopt functions

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

1 files changed, 163 insertions, 3 deletions

diff --git a/vrrpd/vrrp_packet.c b/vrrpd/vrrp_packet.c
index 631b8d7865..d305081574 100644
--- a/vrrpd/vrrp_packet.c
+++ b/vrrpd/vrrp_packet.c
@@ -18,13 +18,37 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  */
 #include <zebra.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
 
-#include "lib/memory.h"
-#include "lib/ipaddr.h"
 #include "lib/checksum.h"
+#include "lib/ipaddr.h"
+#include "lib/memory.h"
 
 #include "vrrp_packet.h"
 
+/* clang-format off */
+const char *vrrp_packet_names[16] = {
+	[0] = "Unknown",
+	[VRRP_TYPE_ADVERTISEMENT] = "ADVERTISEMENT",
+	[2] = "Unknown",
+	[3] = "Unknown",
+	[4] = "Unknown",
+	[5] = "Unknown",
+	[6] = "Unknown",
+	[7] = "Unknown",
+	[8] = "Unknown",
+	[9] = "Unknown",
+	[10] = "Unknown",
+	[11] = "Unknown",
+	[12] = "Unknown",
+	[13] = "Unknown",
+	[14] = "Unknown",
+	[15] = "Unknown",
+};
+/* clang-format on */
+
 ssize_t vrrp_pkt_build(struct vrrp_pkt **pkt, uint8_t vrid, uint8_t prio,
 		       uint16_t max_adver_int, uint8_t numip,
 		       struct ipaddr **ips)
@@ -32,7 +56,7 @@ ssize_t vrrp_pkt_build(struct vrrp_pkt **pkt, uint8_t vrid, uint8_t prio,
 	bool v6 = IS_IPADDR_V6(ips[0]);
 
 	size_t addrsz = v6 ? sizeof(struct in6_addr) : sizeof(struct in_addr);
-	size_t pktsize = sizeof(struct vrrp_hdr) + addrsz * numip;
+	size_t pktsize = VRRP_PKT_SIZE(v6 ? AF_INET6 : AF_INET, numip);
 	*pkt = XCALLOC(MTYPE_TMP, pktsize);
 
 	(*pkt)->hdr.vertype |= VRRP_VERSION << 4;
@@ -50,8 +74,144 @@ ssize_t vrrp_pkt_build(struct vrrp_pkt **pkt, uint8_t vrid, uint8_t prio,
 	}
 	(*pkt)->hdr.chksum = 0;
 
+	/* FIXME: v6 checksum */
 	uint16_t chksum = in_cksum(*pkt, pktsize);
 	(*pkt)->hdr.chksum = htons(chksum);
 
 	return pktsize;
 }
+
+size_t vrrp_pkt_dump(char *buf, size_t buflen, struct vrrp_pkt *pkt)
+{
+	if (buflen < 1)
+		return 0;
+
+	char tmpbuf[BUFSIZ];
+	size_t rs = 0;
+	struct vrrp_hdr *hdr = &pkt->hdr;
+
+	buf[0] = 0x00;
+	snprintf(tmpbuf, sizeof(tmpbuf), "Version: %u\n", (hdr->vertype >> 4));
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "Type: %u (%s)\n",
+		 (hdr->vertype & 0x0F),
+		 vrrp_packet_names[(hdr->vertype & 0x0F)]);
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "VRID: %u\n", hdr->vrid);
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "Priority: %u\n", hdr->priority);
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "Count IPvX: %u\n", hdr->naddr);
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "Max Adver Int: %u\n",
+		 ntohs(hdr->v3.adver_int));
+	rs += strlcat(buf, tmpbuf, buflen);
+	snprintf(tmpbuf, sizeof(tmpbuf), "Checksum: %x\n", ntohs(hdr->chksum));
+	rs += strlcat(buf, tmpbuf, buflen);
+
+	return rs;
+}
+
+ssize_t vrrp_parse_datagram(int family, struct msghdr *m, size_t read,
+			    struct vrrp_pkt **pkt, char *errmsg,
+			    size_t errmsg_len)
+{
+	/* Source (MAC & IP), Dest (MAC & IP) TTL validation done by kernel */
+	size_t addrsz = (family == AF_INET) ? sizeof(struct in_addr)
+					    : sizeof(struct in6_addr);
+
+	size_t pktsize;
+	uint8_t *buf = m->msg_iov->iov_base;
+
+#define VRRP_PKT_VCHECK(cond, _f, ...)                                         \
+	do {                                                                   \
+		if (!(cond)) {                                                 \
+			if (errmsg)                                            \
+				snprintf(errmsg, errmsg_len, (_f),             \
+					 ##__VA_ARGS__);                       \
+			return -1;                                             \
+		}                                                              \
+	} while (0)
+
+	/* IPvX header check */
+
+	if (family == AF_INET) {
+		VRRP_PKT_VCHECK(
+			read >= sizeof(struct ip),
+			"Datagram not large enough to contain IP header");
+
+		struct ip *ip = (struct ip *)buf;
+
+		/* IP total length check */
+		VRRP_PKT_VCHECK(
+			ntohs(ip->ip_len) == read,
+			"IPv4 packet length field does not match # received bytes; %u != %lu",
+			ntohs(ip->ip_len), read);
+
+		/* TTL check */
+		VRRP_PKT_VCHECK(ip->ip_ttl == 255, "IPv4 TTL is not 255");
+
+		*pkt = (struct vrrp_pkt *)(buf + (ip->ip_hl << 2));
+		pktsize = read - (ip->ip_hl << 2);
+
+		/* IP empty packet check */
+		VRRP_PKT_VCHECK(pktsize > 0, "IPv4 packet has no payload");
+	} else if (family == AF_INET6) {
+		struct cmsghdr *c;
+		for (c = CMSG_FIRSTHDR(m); c != NULL; CMSG_NXTHDR(m, c)) {
+			if (c->cmsg_level == IPPROTO_IPV6
+			    && c->cmsg_type == IPV6_HOPLIMIT)
+				break;
+		}
+
+		VRRP_PKT_VCHECK(!!c, "IPv6 Hop Limit not received");
+
+		uint8_t *hoplimit = CMSG_DATA(c);
+		VRRP_PKT_VCHECK(*hoplimit == 255, "IPv6 Hop Limit is not 255");
+
+		*pkt = (struct vrrp_pkt *)buf;
+		pktsize = read;
+	} else {
+		assert(!"Unknown address family");
+	}
+
+	/* Size check */
+	size_t minsize = (family == AF_INET) ? VRRP_MIN_PKT_SIZE_V4
+					     : VRRP_MIN_PKT_SIZE_V6;
+	size_t maxsize = (family == AF_INET) ? VRRP_MAX_PKT_SIZE_V4
+					     : VRRP_MAX_PKT_SIZE_V6;
+	VRRP_PKT_VCHECK(pktsize >= minsize,
+			"VRRP packet is undersized (%lu < %lu)", pktsize,
+			VRRP_MIN_PKT_SIZE);
+	VRRP_PKT_VCHECK(pktsize <= maxsize,
+			"VRRP packet is oversized (%lu > %lu)", pktsize,
+			VRRP_MAX_PKT_SIZE);
+	/* Version check */
+	VRRP_PKT_VCHECK(((*pkt)->hdr.vertype >> 4) != 2, "VRPPv2 unsupported");
+	VRRP_PKT_VCHECK(((*pkt)->hdr.vertype >> 4) == 3, "Bad version %u",
+			(*pkt)->hdr.vertype >> 4);
+	/* Type check */
+	VRRP_PKT_VCHECK(((*pkt)->hdr.vertype & 0x0F) == 1, "Bad type %u",
+			(*pkt)->hdr.vertype & 0x0f);
+	/* Priority check */
+	VRRP_PKT_VCHECK((*pkt)->hdr.priority == 255
+				|| (*pkt)->hdr.priority == 0,
+			"Bad priority %u", (*pkt)->hdr.priority);
+	/* # addresses check */
+	size_t ves = VRRP_PKT_SIZE(family, (*pkt)->hdr.naddr);
+	VRRP_PKT_VCHECK(pktsize == ves, "Packet has incorrect # addresses");
+	/* FIXME: checksum check */
+	/* ... */
+
+	/* Addresses check */
+	char vbuf[INET6_ADDRSTRLEN];
+	uint8_t *p = (uint8_t *)(*pkt)->addrs;
+	for (uint8_t i = 0; i < (*pkt)->hdr.naddr; i++) {
+		VRRP_PKT_VCHECK(inet_ntop(family, p, vbuf, sizeof(vbuf)),
+				"Bad IP address, #%u", i);
+		p += addrsz;
+	}
+
+	/* Everything checks out */
+	return pktsize;
+}