This is the mail archive of the
cygwin
mailing list for the Cygwin project.
Re: UDP/DTLS sockets communication pattern is broken in Cygwin
- From: Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>
- To: cygwin at cygwin dot com
- Date: Thu, 11 Apr 2013 17:21:15 -0400
- Subject: Re: UDP/DTLS sockets communication pattern is broken in Cygwin
- References: <031222CBCF33214AB2EB4ABA279428A30140C1ACA374 at SJCPMAILBOX01 dot citrite dot net>
- Reply-to: cygwin at cygwin dot com
On Thu, Apr 11, 2013 at 02:19:25PM -0700, Oleg Moskalenko wrote:
>Hi All
>
>I found a non-standard behavior of UDP sockets in Cygwin. Normally, people = do not experience it, but the communication pattern that I am going to desc= ribe here is often used in DTLS (actually, this is virtually the only way t= o make OpenSSL working with DTLS on the server side), so I suppose that wit= h the growing DTLS popularity people will experience the problem often.
>
>So this is how to reproduce the problem in "plain" UDP (without actually using DTLS):
>
>1) Server application: open a UDP socket (socket A);
>
>2) Server application: bind socket A to a local server address (say, 172.17.17.107:3478);
>
>3) Server application: wait for a packet from a client application;
>
>4) Client application: open a UDP socket (socket C);
>
>5) Client application: bind socket C it to a local client address (say, 168.16.16.106:12345);
>
>6) Client application: send a UDP packet P1 from socket C to server socket A (to 172.17.17.107:3478);
>
>7) Server application: socket A receives the packet P1 from socket C;
>
>8) Server application: create another UDP socket B;
>
>9) Server application: bind socket B TO THE SAME LOCAL ADDRESS as socket A (172.17.17.107:3478);
>
>10) Server application: connect socket B to the remote address of socket C (168.16.16.106:12345) by calling connect() on the datagram socket B.
>
>11) Server application: send packet P2 from socket B to socket C (to 168.16.16.106:12345).
>
>12) Client application: on socket C, receive packet P2 from socket B (from 172.17.17.107:3478).
>
>13) Client application: from socket C, send packet P3 to the server address 172.17.17.107:3478.
>
>14) Server application: socket A receives the packet P3 from the client socket. ERROR !!!
>
>Step 14 is wrong: the packet P3 must be delivered to socket B, because socket B is "connected"
>to the remote address 168.16.16.106:12345, but socket A is "unconnected".
>Both sockets (A and B) are "bound" to the same server ad= dress (172.17.17.107:3478) but the connected one
>(socket B) must be obtaining packets from the remote address that it is connected to.
>
>This is a very essential functionality for anybody who wants to implement the server-side DTLS communications.
>
>This patterns works in any OS that I tried (all FreeBSD versions, all Linux versions and Solaris) but Cygwin fails, unfortunately.
>
>I am trying to migrate (port) our server application to Cygwin, and it stops us completely. It works everywhere else.
>
>Please take a look if this is something that can be fixed quickly.
How about a simple test case?
cgf
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple