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, 36 insertions, 18 deletions

diff --git a/dhcp.c b/dhcp.c
index d24ef86..7f2191d 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -22,9 +22,11 @@
 #include <stdint.h>
 #include <unistd.h>
 #include <string.h>
+#include <limits.h>
 
 #include "util.h"
 #include "checksum.h"
+#include "packet.h"
 #include "passt.h"
 #include "tap.h"
 #include "dhcp.h"
@@ -257,27 +259,32 @@ static void opt_set_dns_search(struct ctx *c, size_t max_len)
 /**
  * dhcp() - Check if this is a DHCP 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 a DHCP message, 1 if handled, -1 on failure
  */
-int dhcp(struct ctx *c, struct ethhdr *eh, size_t len)
+int dhcp(struct ctx *c, struct pool *p)
 {
-	struct iphdr *iph = (struct iphdr *)(eh + 1);
-	size_t mlen, olen;
+	size_t mlen, len, offset = 0, opt_len, opt_off = 0;
+	struct ethhdr *eh;
+	struct iphdr *iph;
 	struct udphdr *uh;
 	unsigned int i;
 	struct msg *m;
 
-	if (len < sizeof(*eh) + sizeof(*iph))
-		return 0;
+	eh  = packet_get(p, 0, offset, sizeof(*eh),  NULL);
+	offset += sizeof(*eh);
 
-	if (len < sizeof(*eh) + (long)iph->ihl * 4 + sizeof(*uh))
-		return 0;
+	iph = packet_get(p, 0, offset, sizeof(*iph), NULL);
+	if (!eh || !iph)
+		return -1;
 
-	uh = (struct udphdr *)((char *)iph + (long)(iph->ihl * 4));
-	m = (struct msg *)(uh + 1);
+	offset += iph->ihl * 4UL;
+	uh  = packet_get(p, 0, offset, sizeof(*uh),  &mlen);
+	offset += sizeof(*uh);
+
+	if (!uh)
+		return -1;
 
 	if (uh->dest != htons(67))
 		return 0;
@@ -285,18 +292,29 @@ int dhcp(struct ctx *c, struct ethhdr *eh, size_t len)
 	if (c->no_dhcp)
 		return 1;
 
-	mlen = len - sizeof(*eh) - (long)iph->ihl * 4 - sizeof(*uh);
-	if (mlen != ntohs(uh->len) - sizeof(*uh) ||
-	    mlen < offsetof(struct msg, o) ||
+	m   = packet_get(p, 0, offset, offsetof(struct msg, o), &opt_len);
+	if (!m						||
+	    mlen  != ntohs(uh->len) - sizeof(*uh)	||
+	    mlen  <  offsetof(struct msg, o)		||
 	    m->op != BOOTREQUEST)
 		return -1;
 
-	olen = mlen - offsetof(struct msg, o);
-	for (i = 0; i + 2 < olen; i += m->o[i + 1] + 2) {
-		if (m->o[i + 1] + i + 2 >= olen)
+	offset += offsetof(struct msg, o);
+
+	while (opt_off + 2 < opt_len) {
+		uint8_t *olen, *type, *val;
+
+		type = packet_get(p, 0, offset + opt_off,	1,	NULL);
+		olen = packet_get(p, 0, offset + opt_off + 1,	1,	NULL);
+		if (!type || !olen)
+			return -1;
+
+		val =  packet_get(p, 0, offset + opt_off + 2,	*olen,	NULL);
+		if (!val)
 			return -1;
 
-		memcpy(&opts[m->o[i]].c, &m->o[i + 2], m->o[i + 1]);
+		memcpy(&opts[*type].c, val, *olen);
+		opt_off += *olen + 2;
 	}
 
 	if (opts[53].c[0] == DHCPDISCOVER) {