On Aug 21 21:14, Christian Franke wrote: > Corinna Vinschen wrote: > >On Aug 21 18:16, Christian Franke wrote: > >>Corinna Vinschen wrote (in thread "[ITP] libsuexec 1.0"): > >>>Postfix for Cygwin would be *so* nice. Sigh. ... > >>Due to the following problem, Postfix hangs during startup (and blocks any > >>possible "[ITP] postfix ..."): > >> > >>If a AF_UNIX socket is in listen()ing state, a client connect() should > >>succeed immediately. On Cygwin, connect() waits until the server site > >>accept()s the connection. > >> > >>Testcase: > >>... > >> > >> > >>This is likely because fhandler_socket::af_local_connect() waits for some > >>secret. Sending it in af_local_accept() is too late in this case. > >> > >>Unfortunately the event handling of postfix relies on the correct behavior > >>and there is possibly no easy workaround. > >Off the top of my head I don't see one inside the Cygwin DLL :( > > Complex but may work: A fhandler_socket::listen() on a AF_UNIX/SOCK_STREAM > socket starts a thread which accept()s connections, performs the handshake > and puts the new socket descs in a queue. fhandler_socket::accept4() then no > longer calls accept() but waits for the next entry in the queue.
Yeah, that might be very tricky, especially if the executable forks and execs after calling listen. > >The problem is that the package exchange at the start of an > >accept/connect is required to be able to exchange credentials. This in > >turn is required for getpeereid and the SO_PEERCRED socket option which > >is utilized at least by sshd. > > Easier and may work for Postfix: Add a Cygwin specific socket option like > SO_DONT_NEED_PEERCRED which is set immediately after Postfix calls > socket(AF_UNIX, SOCK_STREAM). If set, no handshake occurs on > connect()/accept(). getpeerid()/SO_PEERCRED should fail then. Well, it's not *only* SO_PEERCRED. Another, the older part of the handshake, is about recognizing the peer. Since AF_UNIX sockets don't exist on Windows, Cygwin is using AF_INET sockets under the hood, and so *any* Windows process could accidentally connect to a Cygwin AF_UNIX socket. The handshake also aims to avoid this scenario. Only if the handshake worked, the peers can be sure to talk to another Cygwin process assuming an AF_UNIX socket. A Cygwin-specific socket option which switches off the handshake would disallow this peer recognition. How bad is that? I'm not sure. Another potential solution might be to defer the AF_UNIX handshake to the first send/recv: Whatever the peers do, there is a certain protocol used. That means, there's an implicit understanding who's going to do the first send and who's doing the first recv. So, after connect/accept, both sides of the sockets go into "connected_but_handshake_missing" mode. On the first send/recv, the handshake gets started and if it fails, send/recv return ECONNRESET. This might be easier to implement and might even get rid of the special code in select handling the AF_UNIX handshake after a non-blocking connect. The potential problem here is that this might require another set of changes to cover select... Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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