We can get stuck if a write is going to block because both ends are writing and

neither end is reading.  This is a port of a patch which aims to solve that

problem, but for now it's incomplete because we don't handle partial writes.  A

proper non-blocking implementation would require a bit more work.

diff -up krb5-1.7/src/appl/bsd/defines.h krb5-1.7/src/appl/bsd/defines.h

--- krb5-1.7/src/appl/bsd/defines.h	2008-12-15 15:29:01.000000000 -0500

+++ krb5-1.7/src/appl/bsd/defines.h	2009-06-04 14:18:48.000000000 -0400

@@ -34,6 +34,7 @@ extern int kcmd (int *sock, char **ahost

 		 enum kcmd_proto *protonum /* input and output */

 		 );

+extern int rcmd_stream_has_unsent_data (void);

 extern int rcmd_stream_read (int fd, char *buf, size_t len, int secondary);

 extern int rcmd_stream_write (int fd, char *buf, size_t len, int secondary);

 extern int getport (int * /* portnum */, int * /* addrfamily */);

diff -up krb5-1.7/src/appl/bsd/kcmd.c krb5-1.7/src/appl/bsd/kcmd.c

--- krb5-1.7/src/appl/bsd/kcmd.c	2009-04-15 16:07:15.000000000 -0400

+++ krb5-1.7/src/appl/bsd/kcmd.c	2009-06-04 14:18:48.000000000 -0400

@@ -686,6 +686,11 @@ void rcmd_stream_init_normal()

     output = twrite;

 }

+int rcmd_stream_has_unsent_data (void)

+{

+    return (nstored > 0);

+}

+

 void rcmd_stream_init_krb5(in_keyblock, encrypt_flag, lencheck, am_client,

 			   protonum)

      krb5_keyblock *in_keyblock;

@@ -846,7 +851,8 @@ static int v5_des_read(fd, buf, len, sec

 	cc = krb5_net_read(bsd_context, fd, &c, 1);

 	/* we should check for non-blocking here, but we'd have

 	   to make it save partial reads as well. */

-	if (cc <= 0) return cc; /* read error */

+	if (cc == 0) return nreturned; /* EOF */

+	if (cc < 0) return cc; /* read error */

 	if (cc == 1) {

 	    if (c == 0 || !do_lencheck) break;

 	}

diff -up krb5-1.7/src/appl/bsd/krsh.c krb5-1.7/src/appl/bsd/krsh.c

--- krb5-1.7/src/appl/bsd/krsh.c	2009-06-04 14:18:47.000000000 -0400

+++ krb5-1.7/src/appl/bsd/krsh.c	2009-06-04 14:18:48.000000000 -0400

@@ -115,10 +115,11 @@ main(argc, argv0)

      char **argv0;

 {

     int rem, pid = 0;

-    char *host=0, **ap, buf[RCMD_BUFSIZ], *args, **argv = argv0, *user = 0;

+    char *host=0, **ap, buf[PIPE_BUF], *args, **argv = argv0, *user = 0;

     register int cc;

     struct passwd *pwd;

     fd_set readfrom, ready;

+    fd_set writeto, ready_wr;

     int one = 1;

     struct servent *sp;

     struct servent defaultservent;

@@ -508,9 +509,14 @@ main(argc, argv0)

     FD_ZERO(&readfrom);

     FD_SET(rfd2, &readfrom);

     FD_SET(rem, &readfrom);

+    FD_ZERO(&writeto);

     do {

+	int max_fd;

+	max_fd = (rfd2 > rem) ? rfd2 : rem;

+	max_fd = (max_fd > 2) ? max_fd : 2;

 	ready = readfrom;

-	if (select(((rfd2 > rem) ? rfd2 : rem) + 1, &ready, 0, 0, 0) < 0) {

+	ready_wr = writeto;

+	if (select(max_fd + 1, &ready, &ready_wr, 0, 0) < 0) {

 	    if (errno != EINTR) {

 		perror("select");

 		exit(1);

@@ -518,22 +524,38 @@ main(argc, argv0)

 	    continue;

 	}

 	if (FD_ISSET(rfd2, &ready)) {

-	    errno = 0;

-	    cc = rcmd_stream_read(rfd2, buf, sizeof buf, 1);

-	    if (cc <= 0) {

-		if ((errno != EWOULDBLOCK) && (errno != EAGAIN))

-		    FD_CLR(rfd2, &readfrom);

-	    } else

-	      (void) write(2, buf, (unsigned) cc);

+            FD_SET(2, &writeto);

+	}

+	if (FD_ISSET(2, &ready_wr)) {

+	    do {

+		errno = 0;

+		cc = rcmd_stream_read(rfd2, buf, sizeof buf, 1);

+		if (cc <= 0) {

+		    if ((errno != EWOULDBLOCK) && (errno != EAGAIN)) {

+			FD_CLR(rfd2, &readfrom);

+			break;

+		    }

+		} else

+		  (void) write(2, buf, (unsigned) cc);

+	    } while (rcmd_stream_has_unsent_data());

+	    FD_CLR(2, &writeto);

 	}

 	if (FD_ISSET(rem, &ready)) {

-	    errno = 0;

-	    cc = rcmd_stream_read(rem, buf, sizeof buf, 0);

-	    if (cc <= 0) {

-		if ((errno != EWOULDBLOCK) && (errno != EAGAIN))

-		    FD_CLR(rem, &readfrom);

-	    } else

-	      (void) write(1, buf, (unsigned) cc);

+	    FD_SET(1, &writeto);

+	}

+	if (FD_ISSET(1, &ready_wr)) {

+	    do {

+		errno = 0;

+		cc = rcmd_stream_read(rem, buf, sizeof buf, 0);

+		if (cc <= 0) {

+		    if ((errno != EWOULDBLOCK) && (errno != EAGAIN)) {

+			FD_CLR(rem, &readfrom);

+			break;

+		    }

+		} else

+		  (void) write(1, buf, (unsigned) cc);

+	    } while (rcmd_stream_has_unsent_data());

+	    FD_CLR(1, &writeto);

 	}

     } while (FD_ISSET(rem, &readfrom) || FD_ISSET(rfd2, &readfrom));

     if (nflag == 0)

diff -up krb5-1.7/src/appl/bsd/krshd.c krb5-1.7/src/appl/bsd/krshd.c

--- krb5-1.7/src/appl/bsd/krshd.c	2009-06-04 14:18:47.000000000 -0400

+++ krb5-1.7/src/appl/bsd/krshd.c	2009-06-04 14:18:48.000000000 -0400

@@ -583,7 +583,8 @@ void doit(f, fromp)

     short port;

     int pv[2], pw[2], px[2], cc;

     fd_set ready, readfrom;

-    char buf[RCMD_BUFSIZ], sig;

+    fd_set ready_wr, writeto;

+    char buf[PIPE_BUF], sig;

     struct sockaddr_storage localaddr;

 #ifdef POSIX_SIGNALS

     struct sigaction sa;

@@ -1214,6 +1215,10 @@ void doit(f, fromp)

 	    if (pw[0] > maxfd)

 		maxfd = pw[0];

+	    if (px[1] > maxfd)

+		maxfd = px[1];

+	    FD_ZERO(&writeto);

+

 	    /* read from f, write to px[1] -- child stdin */

 	    /* read from s, signal child */

 	    /* read from pv[0], write to s -- child stderr */

@@ -1221,36 +1226,47 @@ void doit(f, fromp)

 	    do {

 		ready = readfrom;

-		if (select(maxfd + 1, &ready, (fd_set *)0,

+		ready_wr = writeto;

+		if (select(maxfd + 1, &ready, &ready_wr,

 			   (fd_set *)0, (struct timeval *)0) < 0) {

 		    if (errno == EINTR) {

 			continue;

 		    } else {

 			break;

-		}

+		    }

 		}

 		if (port&&FD_ISSET(pv[0], &ready)) {

+		    FD_SET(s, &writeto);

+		    FD_CLR(pv[0], &readfrom);

+		}

+		if (port&&FD_ISSET(s, &ready_wr)) {

 		    /* read from the child stderr, write to the net */

 		    errno = 0;

 		    cc = read(pv[0], buf, sizeof (buf));

-		    if (cc <= 0) {

+		    if ((cc <= 0) ||

+			(rcmd_stream_write(s, buf, (unsigned) cc, 1) != cc)) {

 			shutdown(s, 1+1);

-			FD_CLR(pv[0], &readfrom);

 		    } else {

-			(void) rcmd_stream_write(s, buf, (unsigned) cc, 1);

+			FD_SET(pv[0], &readfrom);

 		    }

+		    FD_CLR(s, &writeto);

 		}

 		if (FD_ISSET(pw[0], &ready)) {

+		    FD_SET(f, &writeto);

+		    FD_CLR(pw[0], &readfrom);

+		}

+		if (FD_ISSET(f, &ready_wr)) {

 		    /* read from the child stdout, write to the net */

 		    errno = 0;

 		    cc = read(pw[0], buf, sizeof (buf));

-		    if (cc <= 0) {

+		    if ((cc <= 0) ||

+			(rcmd_stream_write(f, buf, (unsigned) cc, 0) != cc)) {

 			shutdown(f, 1+1);

-			FD_CLR(pw[0], &readfrom);

 		    } else {

-			(void) rcmd_stream_write(f, buf, (unsigned) cc, 0);

+			FD_SET(pw[0], &readfrom);

 		    }

+		    FD_CLR(f, &writeto);

 		}

 		if (port&&FD_ISSET(s, &ready)) {

 		    /* read from the alternate channel, signal the child */

@@ -1268,12 +1284,15 @@ void doit(f, fromp)

 		    }

 		}

 		if (FD_ISSET(f, &ready)) {

+		    FD_SET(px[1], &writeto);

+		    FD_CLR(f, &readfrom);

+		}

+		if (FD_ISSET(px[1], &ready_wr)) {

 		    /* read from the net, write to child stdin */

 		    errno = 0;

 		    cc = rcmd_stream_read(f, buf, sizeof(buf), 0);

 		    if (cc <= 0) {

 			(void) close(px[1]);

-			FD_CLR(f, &readfrom);

 		    } else {

 		        int wcc;

 		        wcc = write(px[1], buf, (unsigned) cc);

@@ -1281,17 +1300,22 @@ void doit(f, fromp)

 			  /* pipe closed, don't read any more */

 			  /* might check for EPIPE */

 			  (void) close(px[1]);

-			  FD_CLR(f, &readfrom);

-			} else if (wcc != cc) {

-			  syslog(LOG_INFO, "only wrote %d/%d to child", 

-				 wcc, cc);

+			} else {

+			    if (wcc != cc)

+				syslog(LOG_INFO, "only wrote %d/%d to child", 

+				       wcc, cc);

+			    FD_SET(f, &readfrom);

 			}

 		    }

+		    FD_CLR(px[1], &writeto);

 		}

 	    } while ((port&&FD_ISSET(s, &readfrom)) ||

 		     FD_ISSET(f, &readfrom) ||

 		     (port&&FD_ISSET(pv[0], &readfrom) )||

-		     FD_ISSET(pw[0], &readfrom));

+		     FD_ISSET(pw[0], &readfrom) ||

+		     (port&&FD_ISSET(s, &writeto)) ||

+		     FD_ISSET(f, &writeto) ||

+		     FD_ISSET(px[1], &writeto));

 	    ignore_signals();

 #ifdef KERBEROS

 	    syslog(LOG_INFO ,