[Frederic Peters <fpeters@xxxxxxxxxxxxx>]

Hello,

Got this bug report (199908) in the Debian Bug Tracking System.

Later on he posted a patch.


Regards,
        Frederic


bash-2.05b# diff -u follow.c.~1~ follow.c
--- follow.c.~1~	2002-12-03 20:36:10.000000000 -0500
+++ follow.c	2003-07-03 15:01:28.000000000 -0400
@@ -140,12 +140,16 @@
   /* Now check if the packet is for this connection. */
   memcpy(srcx, net_src->data, len);
   memcpy(dstx, net_dst->data, len);
-  if ((memcmp(srcx, ip_address[0], len) != 0 &&
-       memcmp(srcx, ip_address[1], len) != 0) ||
-      (memcmp(dstx, ip_address[0], len) != 0 &&
-       memcmp(dstx, ip_address[1], len) != 0) ||
-      (srcport != tcp_port[0] && srcport != tcp_port[1]) ||
-      (dstport != tcp_port[0] && dstport != tcp_port[1]))
+  if (
+      ! (
+	 !memcmp(srcx, ip_address[0], len) && !memcmp(dstx, ip_address[1], len) &&
+	 srcport == tcp_port[0] && dstport == tcp_port[1]
+	 ) &&
+      ! (
+	 !memcmp(srcx, ip_address[1], len) && !memcmp(dstx, ip_address[0], len) &&
+	 srcport == tcp_port[1] && dstport == tcp_port[0]
+	 )
+      ) 
     return;
 
   /* Initialize our stream chunk.  This data gets written to disk. */

> --- Begin Message ---
> >From fred  Thu Jul  3 22:55:46 2003
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> Subject: Bug#199908: ethereal: Ethereal gets confused if you have symmetric streams
> Reply-To: gsstark@xxxxxxx, 199908@xxxxxxxxxxxxxxx
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> Original-Sender: Gregory Stark <stark@xxxxxxxxxxx>
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> Date: Thu, 03 Jul 2003 14:46:03 -0400
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>
> Package: ethereal
> Version: 0.9.13-1
> Severity: normal
>
> The "Follow TCP Stream" option becomes totally confused if you have two streams
> with swapped port numbers. 
>
> For example, if I'm at host1 and connected to a web server on host2 at the same
> time as host2 is connected to a web server on my machine, and we both happen to
> pick identical source ports, then the Follow TCP Stream doesn't work properly.
>
> What happens is it prints many many messages of the form:
>
> bash-2.05b# ERROR in reassemble_tcp: Too many addresses!
> ERROR in reassemble_tcp: Too many addresses!
> ERROR in reassemble_tcp: Too many addresses!
> ERROR in reassemble_tcp: Too many addresses!
>  
> And the window that shows the TCP Stream shows one side of the each
> conversation instead of both sides of the same conversation.
>
>
> If you think this is an uncommon occurrence, well, it would be except for NAT.
> Under netfilter SNAT and DNAT both try to preserve port numbers whenever
> possible. Consider the case of accessing a service, say port 80, from the
> server itself, but via the external NAT'd address. Both SNAT and DNAT are
> performed which results in two otherwise identical streams from
> internal.sourceport <-> external.80 and external.sourceport <-> internal.80. 
>
> Note that these two otherwise identical streams are not the same stream because
> while the addresses are swapped the ports are not. And only the combination of
> all addresses and ports makes a stream.
>
> In this case what Ethereal shows in the TCP Stream window is the GET request
> repeated twice. It doesn't show any of the HTTP response flow.
>
> Ethereal should key off both the addresses and ports to find matching packets
> for the TCP Stream.
>
>
> -- System Information
> Debian Release: testing/unstable
> Kernel Version: Linux stark.dyndns.tv 2.4.20 #5 Tue Apr 8 08:34:27 EDT 2003 i686 GNU/Linux
>
> Versions of the packages ethereal depends on:
> ii  ethereal-commo 0.9.13-1       Network traffic analyser (common files)
> ii  libatk1.0-0    1.2.4-1        The ATK accessibility toolkit
> ii  libc6          2.3.1-17       GNU C Library: Shared libraries and Timezone
> ii  libglib2.0-0   2.2.2-1        The GLib library of C routines
> ii  libgtk2.0-0    2.2.1-6        The GTK+ graphical user interface library
> ii  libpango1.0-0  1.2.1-4        Layout and rendering of internationalized te
> ii  libpcap0.7     0.7.2-1        System interface for user-level packet captu
> ii  zlib1g         1.1.4-13       compression library - runtime
>
>
>
> --- End Message ---