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, 37 insertions, 23 deletions

diff --git a/util.c b/util.c
index 0adc6b9..f16cd61 100644
--- a/util.c
+++ b/util.c
@@ -38,6 +38,7 @@
 
 #include "util.h"
 #include "passt.h"
+#include "packet.h"
 
 /* For __openlog() and __setlogmask() wrappers, and passt_vsyslog() */
 static int	log_mask;
@@ -156,46 +157,59 @@ void passt_vsyslog(int pri, const char *format, va_list ap)
 	send(log_sock, buf, n, 0);
 }
 
+#define IPV6_NH_OPT(nh)							\
+	((nh) == 0   || (nh) == 43  || (nh) == 44  || (nh) == 50  ||	\
+	 (nh) == 51  || (nh) == 60  || (nh) == 135 || (nh) == 139 ||	\
+	 (nh) == 140 || (nh) == 253 || (nh) == 254)
+
 /**
  * ipv6_l4hdr() - Find pointer to L4 header in IPv6 packet and extract protocol
- * @ip6h:	IPv6 header
+ * @p:		Packet pool, packet number @index has IPv6 header at @offset
+ * @index:	Index of packet in pool
+ * @offset:	Pre-calculated IPv6 header offset
  * @proto:	Filled with L4 protocol number
+ * @dlen:	Data length (payload excluding header extensions), set on return
  *
  * Return: pointer to L4 header, NULL if not found
  */
-char *ipv6_l4hdr(struct ipv6hdr *ip6h, uint8_t *proto)
+char *ipv6_l4hdr(struct pool *p, int index, size_t offset, uint8_t *proto,
+		 size_t *dlen)
 {
-	int offset, len, hdrlen;
 	struct ipv6_opt_hdr *o;
+	struct ipv6hdr *ip6h;
+	char *base;
+	int hdrlen;
 	uint8_t nh;
 
-	len = ntohs(ip6h->payload_len);
-	offset = 0;
+	base = packet_get(p, index, 0, 0, NULL);
+	ip6h = packet_get(p, index, offset, sizeof(*ip6h), dlen);
+	if (!ip6h)
+		return NULL;
 
-	while (offset < len) {
-		if (!offset) {
-			nh = ip6h->nexthdr;
-			hdrlen = sizeof(struct ipv6hdr);
-		} else {
-			o = (struct ipv6_opt_hdr *)(((char *)ip6h) + offset);
-			nh = o->nexthdr;
-			hdrlen = (o->hdrlen + 1) * 8;
-		}
+	offset += sizeof(*ip6h);
 
-		if (nh == 59)
-			return NULL;
+	nh = ip6h->nexthdr;
+	if (!IPV6_NH_OPT(nh))
+		goto found;
+
+	while ((o = packet_get_try(p, index, offset, sizeof(*o), dlen))) {
+		nh = o->nexthdr;
+		hdrlen = (o->hdrlen + 1) * 8;
 
-		if (nh == 0   || nh == 43  || nh == 44  || nh == 50  ||
-		    nh == 51  || nh == 60  || nh == 135 || nh == 139 ||
-		    nh == 140 || nh == 253 || nh == 254) {
+		if (IPV6_NH_OPT(nh))
 			offset += hdrlen;
-		} else {
-			*proto = nh;
-			return (char *)(ip6h + 1) + offset;
-		}
+		else
+			goto found;
 	}
 
 	return NULL;
+
+found:
+	if (nh == 59)
+		return NULL;
+
+	*proto = nh;
+	return base + offset;
 }
 
 /**