bug & patch in ServerAliveInterval (openssh 4.3-p2)

[Darren Tucker]

Hi All.

Markus pointed out that the same problem applies to sshd and that the
earlier change when applied to sshd could still be fooled under some
conditions.

Below is a slightly different method that seems to work OK for both
client and server.

Index: clientloop.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/clientloop.c,v
retrieving revision 1.162
diff -u -p -r1.162 clientloop.c
--- clientloop.c	2006/04/20 09:27:09	1.162
+++ clientloop.c	2006/05/06 05:05:47
@@ -466,6 +466,8 @@ client_wait_until_can_do_something(fd_se
     int *maxfdp, u_int *nallocp, int rekeying)
 {
 	struct timeval tv, *tvp;
+	static time_t lastalive;
+	time_t now;
 	int ret;
 
 	/* Add any selections by the channel mechanism. */
@@ -540,8 +542,15 @@ client_wait_until_can_do_something(fd_se
 		snprintf(buf, sizeof buf, "select: %s\r\n", strerror(errno));
 		buffer_append(&stderr_buffer, buf, strlen(buf));
 		quit_pending = 1;
-	} else if (ret == 0)
-		server_alive_check();
+	} else if (compat20 && options.server_alive_interval) {
+		now = time(NULL);
+		if (lastalive == 0 || FD_ISSET(connection_in, *readsetp)) {
+			lastalive = now;
+		} else if (lastalive + options.server_alive_interval <= now) {
+			lastalive = now;
+			server_alive_check();
+		}
+	}
 }
 
 static void
Index: serverloop.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/serverloop.c,v
retrieving revision 1.135
diff -u -p -r1.135 serverloop.c
--- serverloop.c	2006/03/25 18:30:55	1.135
+++ serverloop.c	2006/05/06 05:05:47
@@ -258,6 +258,8 @@ wait_until_can_do_something(fd_set **rea
     u_int *nallocp, u_int max_time_milliseconds)
 {
 	struct timeval tv, *tvp;
+	static time_t lastalive;
+	time_t now;
 	int ret;
 	int client_alive_scheduled = 0;
 
@@ -342,8 +344,15 @@ wait_until_can_do_something(fd_set **rea
 		memset(*writesetp, 0, *nallocp);
 		if (errno != EINTR)
 			error("select: %.100s", strerror(errno));
-	} else if (ret == 0 && client_alive_scheduled)
-		client_alive_check();
+	} else if (compat20 && options.client_alive_interval) {
+		now = time(NULL);
+		if (lastalive == 0 || FD_ISSET(connection_in, *readsetp)) {
+			lastalive = now;
+		} else if (lastalive + options.client_alive_interval <= now) {
+			lastalive = now;
+			client_alive_check();
+		}
+	}
 
 	notify_done(*readsetp);
 }

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.