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, 27 insertions, 24 deletions

diff --git a/arp.c b/arp.c
index 3195692..bcce804 100644
--- a/arp.c
+++ b/arp.c
@@ -30,53 +30,56 @@
 #include "tap.h"
 
 /**
- * arp() - Check if this is an ARP message, reply as needed
+ * arp() - Check if this is a supported ARP message, reply as needed
  * @c:		Execution context
- * @len:	Total L2 packet length
- * @eh:		Packet buffer, Ethernet header
+ * @p:		Packet pool, single packet with Ethernet buffer
  *
- * Return: 0 if it's not an ARP message, 1 if handled, -1 on failure
+ * Return: 1 if handled, -1 on failure
  */
-int arp(struct ctx *c, struct ethhdr *eh, size_t len)
+int arp(struct ctx *c, struct pool *p)
 {
-	struct arphdr *ah = (struct arphdr *)(eh + 1);
-	struct arpmsg *am = (struct arpmsg *)(ah + 1);
 	unsigned char swap[4];
+	struct ethhdr *eh;
+	struct arphdr *ah;
+	struct arpmsg *am;
+	size_t len;
 
-	if (eh->h_proto != htons(ETH_P_ARP))
-		return 0;
+	eh = packet_get(p, 0, 0,			 sizeof(*eh), NULL);
+	ah = packet_get(p, 0, sizeof(*eh),		 sizeof(*ah), NULL);
+	am = packet_get(p, 0, sizeof(*eh) + sizeof(*ah), sizeof(*am), NULL);
 
-	if (len < sizeof(*eh) + sizeof(*ah) + sizeof(*am))
+	if (!eh || !ah || !am)
 		return -1;
 
-	if (ah->ar_hrd != htons(ARPHRD_ETHER) ||
-	    ah->ar_pro != htons(ETH_P_IP) ||
-	    ah->ar_hln != ETH_ALEN || ah->ar_pln != 4 ||
-	    ah->ar_op != htons(ARPOP_REQUEST))
+	if (ah->ar_hrd != htons(ARPHRD_ETHER)	||
+	    ah->ar_pro != htons(ETH_P_IP)	||
+	    ah->ar_hln != ETH_ALEN		||
+	    ah->ar_pln != 4			||
+	    ah->ar_op  != htons(ARPOP_REQUEST))
 		return 1;
 
 	/* Discard announcements (but not 0.0.0.0 "probes"): we might have the
 	 * same IP address, hide that.
 	 */
-	if (memcmp(am->sip, (unsigned char[4]){ 0, 0, 0, 0 }, 4) &&
-	    !memcmp(am->sip, am->tip, 4))
+	if (memcmp(am->sip, (unsigned char[4]){ 0 }, sizeof(am->tip)) &&
+	    !memcmp(am->sip, am->tip, sizeof(am->sip)))
 		return 1;
 
 	/* Don't resolve our own address, either. */
-	if (!memcmp(am->tip, &c->addr4, 4))
+	if (!memcmp(am->tip, &c->addr4, sizeof(am->tip)))
 		return 1;
 
 	ah->ar_op = htons(ARPOP_REPLY);
-	memcpy(am->tha, am->sha, ETH_ALEN);
-	memcpy(am->sha, c->mac, ETH_ALEN);
+	memcpy(am->tha,		am->sha,	sizeof(am->tha));
+	memcpy(am->sha,		c->mac,		sizeof(am->sha));
 
-	memcpy(swap, am->tip, 4);
-	memcpy(am->tip, am->sip, 4);
-	memcpy(am->sip, swap, 4);
+	memcpy(swap,		am->tip,	sizeof(am->tip));
+	memcpy(am->tip,		am->sip,	sizeof(am->tip));
+	memcpy(am->sip,		swap,		sizeof(am->sip));
 
 	len = sizeof(*eh) + sizeof(*ah) + sizeof(*am);
-	memcpy(eh->h_dest, eh->h_source, ETH_ALEN);
-	memcpy(eh->h_source, c->mac, ETH_ALEN);
+	memcpy(eh->h_dest,	eh->h_source,	sizeof(eh->h_dest));
+	memcpy(eh->h_source,	c->mac,		sizeof(eh->h_source));
 
 	if (tap_send(c, eh, len, 0) < 0)
 		perror("ARP: send");