treewide: Packet abstraction with mandatory boundary checks

Implement a packet abstraction providing boundary and size checks
based on packet descriptors: packets stored in a buffer can be queued
into a pool (without storage of its own), and data can be retrieved
referring to an index in the pool, specifying offset and length.

Checks ensure data is not read outside the boundaries of buffer and
descriptors, and that packets added to a pool are within the buffer
range with valid offset and indices.

This implies a wider rework: usage of the "queueing" part of the
abstraction mostly affects tap_handler_{passt,pasta}() functions and
their callees, while the "fetching" part affects all the guest or tap
facing implementations: TCP, UDP, ICMP, ARP, NDP, DHCP and DHCPv6
handlers.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 25 insertions, 34 deletions

diff --git a/ndp.c b/ndp.c
index 6b1c1a8..b40a0c4 100644
--- a/ndp.c
+++ b/ndp.c
@@ -39,28 +39,23 @@
 /**
  * ndp() - Check for NDP solicitations, reply as needed
  * @c:		Execution context
- * @len:	Total L2 packet length
- * @eh:		Packet buffer, Ethernet header
+ * @ih:		ICMPv6 header
+ * @eh_source:	Source Ethernet address
+ * @saddr	Source IPv6 address
  *
  * Return: 0 if not handled here, 1 if handled, -1 on failure
  */
-int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
+int ndp(struct ctx *c, struct icmp6hdr *ih, unsigned char *eh_source,
+	struct in6_addr *saddr)
 {
-	struct ethhdr *ehr;
-	struct ipv6hdr *ip6h = (struct ipv6hdr *)(eh + 1), *ip6hr;
-	struct icmp6hdr *ih, *ihr;
 	char buf[BUFSIZ] = { 0 };
-	uint8_t proto, *p;
-
-	if (len < sizeof(*ehr) + sizeof(*ip6h) + sizeof(*ih))
-		return 0;
-
-	ih = (struct icmp6hdr *)ipv6_l4hdr(ip6h, &proto);
-	if (!ih)
-		return -1;
+	struct ipv6hdr *ip6hr;
+	struct icmp6hdr *ihr;
+	struct ethhdr *ehr;
+	unsigned char *p;
+	size_t len;
 
-	if (proto != IPPROTO_ICMPV6 ||
-	    ih->icmp6_type < RS || ih->icmp6_type > NA)
+	if (ih->icmp6_type < RS || ih->icmp6_type > NA)
 		return 0;
 
 	if (c->no_ndp)
@@ -71,11 +66,7 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
 	ihr = (struct icmp6hdr *)(ip6hr + 1);
 
 	if (ih->icmp6_type == NS) {
-		if (len < sizeof(*ehr) + sizeof(*ip6h) + sizeof(*ih) +
-			  sizeof(struct in6_addr))
-			return -1;
-
-		if (IN6_IS_ADDR_UNSPECIFIED(&ip6h->saddr))
+		if (IN6_IS_ADDR_UNSPECIFIED(saddr))
 			return 1;
 
 		info("NDP: received NS, sending NA");
@@ -132,10 +123,10 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
 
 		for (n = 0; !IN6_IS_ADDR_UNSPECIFIED(&c->dns6[n]); n++);
 		if (n) {
-			*p++ = 25;			/* RDNSS */
-			*p++ = 1 + 2 * n;		/* length */
-			p += 2;				/* reserved */
-			*(uint32_t *)p = htonl(60);	/* lifetime */
+			*p++ = 25;				/* RDNSS */
+			*p++ = 1 + 2 * n;			/* length */
+			p += 2;					/* reserved */
+			*(uint32_t *)p = htonl(60);		/* lifetime */
 			p += 4;
 
 			for (i = 0; i < n; i++) {
@@ -148,10 +139,10 @@ int ndp(struct ctx *c, struct ethhdr *eh, size_t len)
 		}
 
 		if (!c->no_dhcp_dns_search && dns_s_len) {
-			*p++ = 31;			/* DNSSL */
-			*p++ = (len + 8 - 1) / 8 + 1;	/* length */
-			p += 2;				/* reserved */
-			*(uint32_t *)p = htonl(60);	/* lifetime */
+			*p++ = 31;				/* DNSSL */
+			*p++ = (dns_s_len + 8 - 1) / 8 + 1;	/* length */
+			p += 2;					/* reserved */
+			*(uint32_t *)p = htonl(60);		/* lifetime */
 			p += 4;
 
 			for (i = 0; i < n; i++) {
@@ -185,12 +176,12 @@ dns_done:
 
 	len = (uintptr_t)p - (uintptr_t)ihr - sizeof(*ihr);
 
-	if (IN6_IS_ADDR_LINKLOCAL(&ip6h->saddr))
-		c->addr6_ll_seen = ip6h->saddr;
+	if (IN6_IS_ADDR_LINKLOCAL(saddr))
+		c->addr6_ll_seen = *saddr;
 	else
-		c->addr6_seen = ip6h->saddr;
+		c->addr6_seen = *saddr;
 
-	ip6hr->daddr = ip6h->saddr;
+	ip6hr->daddr = *saddr;
 	if (IN6_IS_ADDR_LINKLOCAL(&c->gw6))
 		ip6hr->saddr = c->gw6;
 	else
@@ -207,7 +198,7 @@ dns_done:
 	ip6hr->hop_limit = 255;
 
 	len += sizeof(*ehr) + sizeof(*ip6hr) + sizeof(*ihr);
-	memcpy(ehr->h_dest, eh->h_source, ETH_ALEN);
+	memcpy(ehr->h_dest, eh_source, ETH_ALEN);
 	memcpy(ehr->h_source, c->mac, ETH_ALEN);
 	ehr->h_proto = htons(ETH_P_IPV6);