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, 26 insertions, 20 deletions

diff --git a/udp.c b/udp.c
index e22f3ac..9032e47 100644
--- a/udp.c
+++ b/udp.c
@@ -951,35 +951,35 @@ void udp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events,
  * @c:		Execution context
  * @af:		Address family, AF_INET or AF_INET6
  * @addr:	Destination address
- * @msg:	Input messages
- * @count:	Message count
+ * @p:		Pool of UDP packets, with UDP headers
  * @now:	Current timestamp
  *
  * Return: count of consumed packets
  *
  * #syscalls sendmmsg
  */
-int udp_tap_handler(struct ctx *c, int af, void *addr,
-		    struct tap_l4_msg *msg, int count, struct timespec *now)
+int udp_tap_handler(struct ctx *c, int af, void *addr, struct pool *p,
+		    struct timespec *now)
 {
-	/* The caller already checks that all the messages have the same source
-	 * and destination, so we can just take those from the first message.
-	 */
-	struct udphdr *uh = (struct udphdr *)(pkt_buf + msg[0].pkt_buf_offset);
 	struct mmsghdr mm[UIO_MAXIOV] = { 0 };
 	struct iovec m[UIO_MAXIOV];
 	struct sockaddr_in6 s_in6;
 	struct sockaddr_in s_in;
 	struct sockaddr *sa;
+	int i, s, count = 0;
 	in_port_t src, dst;
+	struct udphdr *uh;
 	socklen_t sl;
-	int i, s;
 
 	(void)c;
 
-	if (msg[0].l4_len < sizeof(*uh))
+	uh = packet_get(p, 0, 0, sizeof(*uh), NULL);
+	if (!uh)
 		return 1;
 
+	/* The caller already checks that all the messages have the same source
+	 * and destination, so we can just take those from the first message.
+	 */
 	src = ntohs(uh->source);
 	dst = ntohs(uh->dest);
 
@@ -998,8 +998,8 @@ int udp_tap_handler(struct ctx *c, int af, void *addr,
 						     .udp.port = src };
 
 			s = sock_l4(c, AF_INET, IPPROTO_UDP, src, 0, uref.u32);
-			if (s <= 0)
-				return count;
+			if (s < 0)
+				return p->count;
 
 			udp_tap_map[V4][src].sock = s;
 			bitmap_set(udp_act[V4][UDP_ACT_TAP], src);
@@ -1050,8 +1050,8 @@ int udp_tap_handler(struct ctx *c, int af, void *addr,
 
 			s = sock_l4(c, AF_INET6, IPPROTO_UDP, src, bind_to,
 				    uref.u32);
-			if (s <= 0)
-				return count;
+			if (s < 0)
+				return p->count;
 
 			udp_tap_map[V6][src].sock = s;
 			bitmap_set(udp_act[V6][UDP_ACT_TAP], src);
@@ -1060,18 +1060,26 @@ int udp_tap_handler(struct ctx *c, int af, void *addr,
 		udp_tap_map[V6][src].ts = now->tv_sec;
 	}
 
-	for (i = 0; i < count; i++) {
+	for (i = 0; i < (int)p->count; i++) {
 		struct udphdr *uh_send;
+		size_t len;
+
+		uh_send = packet_get(p, i, 0, sizeof(*uh), &len);
+		if (!uh_send)
+			return p->count;
+		if (!len)
+			continue;
 
-		uh_send = (struct udphdr *)(msg[i].pkt_buf_offset + pkt_buf);
 		m[i].iov_base = (char *)(uh_send + 1);
-		m[i].iov_len = msg[i].l4_len - sizeof(*uh_send);
+		m[i].iov_len = len;
 
 		mm[i].msg_hdr.msg_name = sa;
 		mm[i].msg_hdr.msg_namelen = sl;
 
 		mm[i].msg_hdr.msg_iov = m + i;
 		mm[i].msg_hdr.msg_iovlen = 1;
+
+		count++;
 	}
 
 	count = sendmmsg(s, mm, count, MSG_NOSIGNAL);
@@ -1172,13 +1180,11 @@ static void udp_splice_iov_init(void)
  *
  * Return: 0 on success, -1 on failure
  */
-int udp_sock_init(struct ctx *c, struct timespec *now)
+int udp_sock_init(struct ctx *c)
 {
 	union udp_epoll_ref uref = { .udp.bound = 1 };
 	int dst, s;
 
-	(void)now;
-
 	for (dst = 0; dst < USHRT_MAX; dst++) {
 		if (!bitmap_isset(c->udp.port_to_tap, dst))
 			continue;