Note and patch about strange UDP packets

[Michael Stefaniuc]

Florian Echtler wrote:
> Hi everybody,
> 
> we are using a certain tracking software from Advanced Realtime
> Tracking. This is a windows software, but we decided yesterday that it
> would be more flexible to be able to use it under Linux, too, so I gave
> it a try with Wine.
> 
> As this software communicates with customized (expensive) cameras via
> UDP, I noted a strange bug in the Wine debug channel "winsock": the
> software was sending UDP packets to IP _254_.255.255.255 (note the first
> octet). After some experimentation, I noticed that while Windows just
> sends this as a broadcast packet, Linux rejects this address, because
> the corresponding RFC states that the network 240.0.0.0/4 is reserved
> and should not be used.
> 
> I therefore build a small patch which checks for these strange adresses
> and replaces them by broadcast adresses. This enabled our software to
> work. However, the question now is whether it makes sense to include
> this patch into Wine? On the one hand, it increases the similarity
If an application really depends on a Windows bug to work correctly then 
chances are good that the patch will be accepted. But you have to write 
a test case for this behavior. And you'll have to put in a big fat 
comment in the code why you had to do that.

> between Wine's behaviour and Windows's, OTOH it decreases Wine's RFC
> compliance..

bye
	michael

> ------------------------------------------------------------------------
> 
> --- dlls/winsock/socket.c	2006-02-15 17:02:53.000000000 +0100
> +++ dlls/winsock/socket.c	2006-09-14 15:30:18.000000000 +0200
> @@ -1392,6 +1392,8 @@
>  {
>      struct msghdr hdr;
>      int n = -1;
> +		u_int32_t* target;
> +
>      TRACE( "fd %d, iovec %p, count %d addr %s, len %d, flags %lx\n",
>             fd, iov, count, debugstr_sockaddr(to), tolen, dwFlags);
>  
> @@ -1443,6 +1445,13 @@
>      hdr.msg_flags = 0;
>  #endif
>  
> +		target = &(((struct sockaddr_in*)(hdr.msg_name))->sin_addr.s_addr);
> +		if ( ((*target) & 0x000000F0) == 0x000000F0) {
> +			fprintf(stderr,"FIXME: i cheated and changed reserved IP address 240.*/4 to 255.*.\n");
> +			*target |= 0x000000FF;
> +			//printf("%x\n",*target);
> +		}
> +
>      n = sendmsg(fd, &hdr, dwFlags);
>  
>  out:
> 
> 
> ------------------------------------------------------------------------
> 
> 


-- 
Michael Stefaniuc               Tel.: +49-711-96437-199
Sr. Network Engineer            Fax.: +49-711-96437-111
Red Hat GmbH                    Email: mstefani at redhat.com
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D-70178 Stuttgart