Bug #844 PR# 846: reject invalid header length packets

Triggers when attempting a checksum update but packet length does not match header length. Example: ``` tcprewrite -i test.pcap -o test2.rewrite_1ttl --ttl=58 Warning: skipping packet 11 because caplen 122 minus L2 length 22 does not equal IPv4 header length 255. Consider option '--fixhdrlen'. Warning: skipping packet 12 because caplen 114 minus L2 length 14 does not equal IPv4 header length 84. Consider option '--fixhdrlen'. Warning: skipping packet 14 because caplen 60 minus L2 length 14 does not equal IPv4 header length 28. Consider option '--fixhdrlen'. Warning: skipping packet 15 because caplen 60 minus L2 length 14 does not equal IPv4 header length 28. Consider option '--fixhdrlen'. Warning: skipping packet 16 because caplen 60 minus L2 length 14 does not equal IPv4 header length 28. Consider option '--fixhdrlen'. ```
appneta · Jun 1, 2024 · 4789dee · 4789dee
1 parent 859728b
commit 4789dee
Showing 1 changed file with 7 additions and 6 deletions.
diff --git a/src/tcpedit/edit_packet.c b/src/tcpedit/edit_packet.c
@@ -78,12 +78,13 @@ fix_ipv4_checksums(tcpedit_t *tcpedit, struct pcap_pkthdr *pkthdr, ipv4_hdr_t *i
     /* calc the L4 checksum if we have the whole packet && not a frag or first frag */
     if (pkthdr->caplen == pkthdr->len && (htons(ip_hdr->ip_off) & (IP_MF | IP_OFFMASK)) == 0) {
         if (ip_len != (int)(pkthdr->caplen - l2len)) {
-            tcpedit_seterr(tcpedit,
-                           "caplen minus L2 length %u does IPv4 header length %u: pkt=" COUNTER_SPEC,
-                           pkthdr->caplen - l2len,
-                           ip_len,
-                           tcpedit->runtime.packetnum);
-            return TCPEDIT_ERROR;
+            tcpedit_setwarn(tcpedit,
+                            "skipping packet " COUNTER_SPEC " because caplen %u minus L2 length %u does not equal IPv4 header length %u. Consider option '--fixhdrlen'.",
+                            tcpedit->runtime.packetnum,
+                            pkthdr->caplen,
+                            l2len,
+                            ip_len);
+            return TCPEDIT_WARN;
         }
         ret1 = do_checksum(tcpedit,
                            (u_char *)ip_hdr,