Bug #594 Add some additional headroom to cached packets

When using '--preload-pcap' option any additional VLAN headers
results in Heap Buffer Overflow. Add 512 bytes additional buffer
space.

TODO: Add intelligence to understand when and how much memory
to allocate/reallocate based on tcpedit function.

src/defines.h.in

@@ -161,6 +161,8 @@ typedef struct tcpr_speed_s {
                                          * couple VLAN headers or a L2 header
                                          */
 
+#define PACKET_HEADROOM 512     /* additional headroom allocated for packets to accommodate editing */
+
 #define DNS_RESOLVE 1
 #define DNS_DONT_RESOLVE 0
 

src/send_packets.c

@@ -1055,7 +1055,7 @@ get_next_packet(tcpreplay_t *ctx, pcap_t *pcap, struct pcap_pkthdr *pkthdr, int
                     (*prev_packet)->next = NULL;
                     pktlen = pkthdr->len;
 
-                    (*prev_packet)->pktdata = safe_malloc(pktlen);
+                    (*prev_packet)->pktdata = safe_malloc(pktlen + PACKET_HEADROOM);
                     memcpy((*prev_packet)->pktdata, pktdata, pktlen);
                     memcpy(&((*prev_packet)->pkthdr), pkthdr, sizeof(struct pcap_pkthdr));
                 }