From: Arlene Berry <aberry@likewise.com>
To: "krb5-bugs@mit.edu" <krb5-bugs@mit.edu>
Subject: blocking recv caused our server to hang
Thread-Topic: blocking recv caused our server to hang
Thread-Index: AcxH9Do3LdwtoXlLTDa653CHbfOjBA==
Date: Thu, 21 Jul 2011 22:19:08 +0000
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We've had this patch in our local source for a long time and the original description says select reported a socket as ready for reading but the recv blocked which caused our server to hang.  This was seen on multiple versions of Solaris and possibly elsewhere.  We solved it by changing all sockets to non-blocking.  

Index: src/lib/krb5/os/sendto_kdc.c
===================================================================
--- src/lib/krb5/os/sendto_kdc.c	(revision 25023)
+++ src/lib/krb5/os/sendto_kdc.c	(working copy)
@@ -758,6 +758,8 @@
 {
     int fd, e;
     unsigned int ssflags;
+    static const int one = 1;
+    static const struct linger lopt = { 0, 0 };
 
     dprint("start_connection(@%p)\ngetting %s socket in family %d...", state,
            state->socktype == SOCK_STREAM ? "stream" : "dgram", state->family);
@@ -769,14 +771,11 @@
     }
     set_cloexec_fd(fd);
     /* Make it non-blocking.  */
+    if (ioctlsocket(fd, FIONBIO, (const void *) &one))
+        dperror("sendto_kdc: ioctl(FIONBIO)");
+    if (setsockopt(fd, SOL_SOCKET, SO_LINGER, &lopt, sizeof(lopt)))
+        dperror("sendto_kdc: setsockopt(SO_LINGER)");
     if (state->socktype == SOCK_STREAM) {
-        static const int one = 1;
-        static const struct linger lopt = { 0, 0 };
-
-        if (ioctlsocket(fd, FIONBIO, (const void *) &one))
-            dperror("sendto_kdc: ioctl(FIONBIO)");
-        if (setsockopt(fd, SOL_SOCKET, SO_LINGER, &lopt, sizeof(lopt)))
-            dperror("sendto_kdc: setsockopt(SO_LINGER)");
         TRACE_SENDTO_KDC_TCP_CONNECT(context, state);
     }