Add option to turn on/off fix packet header length

src/tcpedit/parse_args.c

@@ -95,6 +95,12 @@ tcpedit_post_args(tcpedit_t *tcpedit)
     if (HAVE_OPT(FIXCSUM))
         tcpedit->fixcsum = true;
 
+    /* --fixhdrlen */
+    if (HAVE_OPT(FIXHDRLEN))
+        tcpedit->fixhdrlen = true;
+    else
+        tcpedit->fixhdrlen = false;
+
     /* --efcs */
     if (HAVE_OPT(EFCS))
         tcpedit->efcs = true;

src/tcpedit/tcpedit.c

@@ -18,7 +18,7 @@
  *   along with the Tcpreplay Suite.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "defines.h"
 #include "config.h"
 #include "common.h"
 #include "edit_packet.h"
@@ -44,7 +44,7 @@
  *          1 on change
  */
 int
 tcpedit_packet(tcpedit_t *tcpedit, struct pcap_pkthdr **pkthdr, u_char **pktdata, tcpr_dir_t direction)
 {
     bool fuzz_once = tcpedit->fuzz_seed != 0;
     ipv4_hdr_t *ip_hdr;
@@ -315,12 +315,21 @@
         }
     }
 
-    /* ensure IP header length is correct */
-    if (ip_hdr != NULL) {
-        fix_ipv4_length(*pkthdr, ip_hdr, l2len);
-        needtorecalc = 1;
-    } else if (ip6_hdr != NULL) {
-        needtorecalc |= fix_ipv6_length(*pkthdr, ip6_hdr, l2len);
+    /* fixhdrlen option ensure IP header length is correct */
+    /* do we need to fix checksums? -- must always do this last! */
+    if (tcpedit->fixhdrlen) {
+        /* ensure IP header length is correct */
+        int changed = 0;
+        if (ip_hdr != NULL) {
+            fix_ipv4_length(*pkthdr, ip_hdr, l2len);
+            changed = 1;
+        } else if (ip6_hdr != NULL) {
+            changed = fix_ipv6_length(*pkthdr, ip6_hdr, l2len);
+        }
+        /* did the packet change? then needtorecalc checksum */
+        if (changed > 0) {
+            needtorecalc |= changed;
+        }
     }
 
     /* do we need to fix checksums? -- must always do this last! */

src/tcpedit/tcpedit_api.c

@@ -18,7 +18,7 @@
  *   along with the Tcpreplay Suite.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include "defines.h"
 #include "config.h"
 #include "dlt_utils.h"
 #include "portmap.h"
@@ -136,6 +136,17 @@
     return TCPEDIT_OK;
 }
 
+/**
+ * \brief should we fix(?) header length?
+ */
+int
+tcpedit_set_fixhdrlen(tcpedit_t *tcpedit, bool value)
+{
+    assert(tcpedit);
+    tcpedit->fixhdrlen = value;
+    return TCPEDIT_OK;
+}
+
 /**
  * \brief should we remove the EFCS from the frame?
  */

src/tcpedit/tcpedit_api.h

@@ -29,19 +29,20 @@
  * so when using the config API you must manually specify it using one of
  * the following functions
  */
 int tcpedit_set_encoder_dltplugin_byid(tcpedit_t *, int);
 int tcpedit_set_encoder_dltplugin_byname(tcpedit_t *, const char *);
 
 /**
  * setters always return TCPEDIT_OK on success or TCPEDIT_ERROR
  * if there is a problem.  You can use tcpedit_geterr() to get the reason
  * for the failure
  */
 int tcpedit_set_skip_broadcast(tcpedit_t *, bool);
 int tcpedit_set_fixlen(tcpedit_t *, tcpedit_fixlen);
 int tcpedit_set_fixcsum(tcpedit_t *, bool);
+int tcpedit_set_fixhdrlen(tcpedit_t *, bool);
 int tcpedit_set_efcs(tcpedit_t *, bool);
 int tcpedit_set_ttl_mode(tcpedit_t *, tcpedit_ttl_mode);
 int tcpedit_set_ttl_value(tcpedit_t *, uint8_t);
 int tcpedit_set_tos(tcpedit_t *, uint8_t);
 int tcpedit_set_tclass(tcpedit_t *, uint8_t);

src/tcpedit/tcpedit_opts.def

@@ -170,6 +170,19 @@ fixed.  Automatically enabled for packets modified with @samp{--seed},
 EOText;
 };
 
+flag = {
+    name        = fixhdrlen;
+    // value       = C;
+    descrip     = "fix IP/TCP header len";
+    doc         = <<- EOText
+By default, tcpreplay will send packets with the original packet length,
+However, you may want the packet length revised to minimum packet size.
+Using this option, tcpreplay will rewrite (fix) the packet length,
+and recalculate checksums.
+Caution: undesired packet changes may occur when this option is specified.
+EOText;
+};
+
 flag = {
     name        = mtu;
     value       = m;

src/tcpedit/tcpedit_types.h

@@ -147,6 +147,9 @@ typedef struct {
 
     uint32_t fuzz_seed;
     uint32_t fuzz_factor;
+
+    /* fix header length */
+    bool fixhdrlen;
 } tcpedit_t;
 
 #ifdef __cplusplus

src/tcpreplay_api.h

@@ -178,6 +178,9 @@ typedef struct tcpreplay_s {
     uint32_t skip_packets;
     bool first_time;
 
+    /* fix header length */
+    bool fixhdrlen;
+
     /* counter stats */
     tcpreplay_stats_t stats;
     tcpreplay_stats_t static_stats; /* stats returned by tcpreplay_get_stats() */