Try using the ip_len header field to guess the input buffer's size.

1 files changed, 11 insertions, 1 deletions

diff --git a/libnet/src/libnet_checksum.c b/libnet/src/libnet_checksum.c
index fcbde5b..a978555 100644
--- a/libnet/src/libnet_checksum.c
+++ b/libnet/src/libnet_checksum.c
@@ -152,8 +152,18 @@ static int check_ip_payload_size(libnet_t*l, const uint8_t *iphdr, int ip_hl, in
 int
 libnet_do_checksum(libnet_t *l, uint8_t *iphdr, int protocol, int h_len)
 {
+    uint16_t ip_len = 0;
+    struct libnet_ipv4_hdr* ip4 = (struct libnet_ipv4_hdr *)iphdr;
+    struct libnet_ipv6_hdr* ip6 = (struct libnet_ipv6_hdr *)iphdr;
+
+    if(ip4->ip_v == 4) {
+        ip_len = ntohs(ip4->ip_len);
+    } else {
+        ip_len = ntohs(ip6->ip_len);
+    }
+
     return libnet_inet_checksum(l, iphdr, protocol, h_len,
-            iphdr, iphdr + LIBNET_IPV4_H + h_len
+            iphdr, iphdr + ip_len
             );
 }