If we were handed a fragmented packet, don't do anything that depends on

knowing the actual length of the packet, as we don't know that length
(IP fragments don't contain the length of the full packet - you don't
know how big the reassembled packet is until you reassemble it).

We don't have to worry about dissecting the TCP header in them, though.

svn path=/trunk/; revision=7703

1 files changed, 48 insertions, 47 deletions

diff --git a/packet-tcp.c b/packet-tcp.c
index fd81d6a579..116d71158a 100644
--- a/packet-tcp.c
+++ b/packet-tcp.c
@@ -1,7 +1,7 @@
 /* packet-tcp.c
  * Routines for TCP packet disassembly
  *
- * $Id: packet-tcp.c,v 1.193 2003/05/20 10:14:20 sahlberg Exp $
+ * $Id: packet-tcp.c,v 1.194 2003/05/21 05:43:27 guy Exp $
  *
  * Ethereal - Network traffic analyzer
  * By Gerald Combs <gerald@ethereal.com>
@@ -2080,7 +2080,7 @@ dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
   gint       fpos = 0, i;
   guint      bpos;
   guint      optlen;
-  guint32    nxtseq;
+  guint32    nxtseq = 0;
   guint      reported_len;
   vec_t      cksum_vec[4];
   guint32    phdr[2];
@@ -2146,44 +2146,36 @@ dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
   tcph->th_win = tvb_get_ntohs(tvb, offset + 14);
   tcph->th_hlen = hi_nibble(th_off_x2) * 4;  /* TCP header length, in bytes */
 
+  /*
+   * If we've been handed an IP fragment, we don't know how big the TCP
+   * segment is, so don't do anything that requires that we know that.
+   */
   reported_len = tvb_reported_length(tvb);
 
-  /* make nmap happy.  nmap sends out tcp segments that are fragmented at the
-     ip layer with the first fragment only containing the first 16 bytes of
-     the normal 20 byte tcp header.
-     TCP segments should not be fragmented at the ip layer normally so this
-     would probably either be nmap in action fingerprinting someone
-     or a tcp layer bug.
-  */
-  if (reported_len<20 || (reported_len<tcph->th_hlen)){
-    proto_tree_add_text(tcp_tree, tvb, offset, 0,
-        "Short segment. Segment/fragment does not contain a full TCP header (might be NMAP or someone else deliberately sending unusual packets)");
-    return;
-  }
+  if (!pinfo->fragmented) {
+    /* Compute the length of data in this segment. */
+    tcph->th_seglen = reported_len - tcph->th_hlen;
 
-  /* Compute the length of data in this segment. */
-  tcph->th_seglen = reported_len - tcph->th_hlen;
+    if (tree) { /* Add the seglen as an invisible field */
 
-  if (tree) { /* Add the seglen as an invisible field */
+      proto_tree_add_uint_hidden(ti, hf_tcp_len, tvb, offset, 4, tcph->th_seglen);
 
-    proto_tree_add_uint_hidden(ti, hf_tcp_len, tvb, offset, 4, tcph->th_seglen);
+    }
 
-  }
+    /* handle TCP seq# analysis parse all new segments we see */
+    if(tcp_analyze_seq){
+        if(!(pinfo->fd->flags.visited)){
+            tcp_analyze_sequence_number(pinfo, tcph->th_seq, tcph->th_ack, tcph->th_seglen, tcph->th_flags, tcph->th_win);
+        }
+        if(tcp_relative_seq){
+            tcp_get_relative_seq_ack(pinfo->fd->num, &(tcph->th_seq), &(tcph->th_ack));
+        }
+    }
 
-  /* handle TCP seq# analysis parse all new segments we see */
-  if(tcp_analyze_seq){
-      if(!(pinfo->fd->flags.visited)){
-          tcp_analyze_sequence_number(pinfo, tcph->th_seq, tcph->th_ack, tcph->th_seglen, tcph->th_flags, tcph->th_win);
-      }
-      if(tcp_relative_seq){
-          tcp_get_relative_seq_ack(pinfo->fd->num, &(tcph->th_seq), &(tcph->th_ack));
-      }
+    /* Compute the sequence number of next octet after this segment. */
+    nxtseq = tcph->th_seq + tcph->th_seglen;
   }
 
-
-  /* Compute the sequence number of next octet after this segment. */
-  nxtseq = tcph->th_seq + tcph->th_seglen;
-
   if (check_col(pinfo->cinfo, COL_INFO) || tree) {
     for (i = 0; i < 8; i++) {
       bpos = 1 << i;
@@ -2228,11 +2220,16 @@ dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
   }
 
   if (tree) {
-    if (tcp_summary_in_tree)
-      proto_item_append_text(ti, ", Ack: %u, Len: %u", tcph->th_ack, tcph->th_seglen);
+    if (tcp_summary_in_tree) {
+      proto_item_append_text(ti, ", Ack: %u", tcph->th_ack);
+      if (!pinfo->fragmented)
+        proto_item_append_text(ti, ", Len: %u", tcph->th_seglen);
+    }
     proto_item_set_len(ti, tcph->th_hlen);
-    if (nxtseq != tcph->th_seq) {
-      proto_tree_add_uint(tcp_tree, hf_tcp_nxtseq, tvb, offset, 0, nxtseq);
+    if (!pinfo->fragmented) {
+      if (nxtseq != tcph->th_seq) {
+        proto_tree_add_uint(tcp_tree, hf_tcp_nxtseq, tvb, offset, 0, nxtseq);
+      }
     }
     if (tcph->th_flags & TH_ACK)
       proto_tree_add_uint(tcp_tree, hf_tcp_ack, tvb, offset + 8, 4, tcph->th_ack);
@@ -2363,8 +2360,10 @@ dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
   } else
     tcpinfo.urgent = FALSE;
 
-  if (check_col(pinfo->cinfo, COL_INFO))
-    col_append_fstr(pinfo->cinfo, COL_INFO, " Len=%u", tcph->th_seglen);
+  if (!pinfo->fragmented) {
+    if (check_col(pinfo->cinfo, COL_INFO))
+      col_append_fstr(pinfo->cinfo, COL_INFO, " Len=%u", tcph->th_seglen);
+  }
 
   /* Decode TCP options, if any. */
   if (tree && tcph->th_hlen > TCPH_MIN_LEN) {
@@ -2385,16 +2384,18 @@ dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
      (it could be an ACK-only packet) */
   length_remaining = tvb_length_remaining(tvb, offset);
 
-  if( data_out_file ) {
-    reassemble_tcp( tcph->th_seq,		/* sequence number */
-        tcph->th_seglen,			/* data length */
-        tvb_get_ptr(tvb, offset, length_remaining),	/* data */
-        length_remaining,		/* captured data length */
-        ( tcph->th_flags & TH_SYN ),		/* is syn set? */
-        &pinfo->net_src,
-	&pinfo->net_dst,
-	pinfo->srcport,
-	pinfo->destport);
+  if (!pinfo->fragmented) {
+    if( data_out_file ) {
+      reassemble_tcp( tcph->th_seq,		/* sequence number */
+          tcph->th_seglen,			/* data length */
+          tvb_get_ptr(tvb, offset, length_remaining),	/* data */
+          length_remaining,		/* captured data length */
+          ( tcph->th_flags & TH_SYN ),		/* is syn set? */
+          &pinfo->net_src,
+          &pinfo->net_dst,
+          pinfo->srcport,
+          pinfo->destport);
+    }
   }
 
   if (length_remaining != 0) {