[Bug 52] ssh hangs on exit

bugzilla-daemon at mindrot.org
Sun, 21 Jan 2007 04:54:22 -0000

------- Comment #33 from djm at mindrot.org  2007-01-21 15:54 -------
(From update of attachment 1215)
Sorry for taking so long to review this. Some comments on the diff (I'd
really like to see this in 4.6p1)

>Index: channels.c
>==================================================================>RCS
file: /usr/local/src/security/openssh/cvs/openssh/channels.c,v
>retrieving revision 1.248
>diff -u -p -r1.248 channels.c
>--- channels.c	30 Aug 2006 01:07:40 -0000	1.248
>+++ channels.c	27 Nov 2006 03:39:26 -0000
>@@ -1449,10 +1449,10 @@ channel_handle_rfd(Channel *c, fd_set *r
> 	int len;
>
> 	if (c->rfd != -1 &&
>-	    FD_ISSET(c->rfd, readset)) {
>+	    (c->detach_close || FD_ISSET(c->rfd, readset))) {

Is c->detach_close used here to chose "session channels that have
exitied but not yet closed"? or something else?

> 		errno = 0;
> 		len = read(c->rfd, buf, sizeof(buf));
>-		if (len < 0 && (errno == EINTR || errno == EAGAIN))
>+		if (len < 0 && errno == EINTR)

Can the second condition instead be made:

&& (errno == EINTR || c->detach_close || errno == EAGAIN)

This would limit the scope of the change to only session channels which
have already received a SIGCHLD.

>@@ -1604,11 +1604,11 @@ channel_handle_efd(Channel *c, fd_set *r
> 				c->local_consumed += len;
> 			}
> 		} else if (c->extended_usage == CHAN_EXTENDED_READ &&
>-		    FD_ISSET(c->efd, readset)) {
>+		    (c->detach_close || FD_ISSET(c->efd, readset))) {
> 			len = read(c->efd, buf, sizeof(buf));
> 			debug2("channel %d: read %d from efd %d",
> 			    c->self, len, c->efd);
>-			if (len < 0 && (errno == EINTR || errno == EAGAIN))
>+			if (len < 0 && errno == EINTR)

Likewise.

>Index: serverloop.c
>==================================================================>RCS
file: /usr/local/src/security/openssh/cvs/openssh/serverloop.c,v
>retrieving revision 1.150
>diff -u -p -r1.150 serverloop.c
>--- serverloop.c	23 Oct 2006 17:02:41 -0000	1.150
>+++ serverloop.c	27 Nov 2006 03:37:16 -0000
>@@ -280,6 +280,7 @@ wait_until_can_do_something(fd_set **rea
> 	struct timeval tv, *tvp;
> 	int ret;
> 	int client_alive_scheduled = 0;
>+	int program_alive_scheduled = 0;
>
> 	/*
> 	 * if using client_alive, set the max timeout accordingly,
>@@ -317,6 +318,7 @@ wait_until_can_do_something(fd_set **rea
> 		 * the client, try to get some more data from the program.
> 		 */
> 		if (packet_not_very_much_data_to_write()) {
>+			program_alive_scheduled = child_terminated;

Why not just use child_terminated directly here? Is it because of
children exiting during select()

>-	} else if (ret == 0 && client_alive_scheduled)
>-		client_alive_check();
>+	} else {
>+		if (ret == 0 && client_alive_scheduled)
>+			client_alive_check();
>+		if (program_alive_scheduled && fdin_is_tty) {
>+			if (!fdout_eof)
>+				FD_SET(fdout, *readsetp);
>+			if (!fderr_eof)
>+				FD_SET(fderr, *readsetp);
>+		}
>+	}

I think the condition for this if() should include !compat20 (I know
that fdin_is_tty is never set for !compat20, but you have to hunt for
it).

>
> 	notify_done(*readsetp);
> }
>@@ -407,7 +417,7 @@ process_input(fd_set *readset)
> 	if (!fdout_eof && FD_ISSET(fdout, readset)) {
> 		errno = 0;
> 		len = read(fdout, buf, sizeof(buf));
>-		if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
>+		if (len < 0 && errno == EINTR) {
> 			/* do nothing */
> #ifndef PTY_ZEROREAD
> 		} else if (len <= 0) {
>@@ -425,7 +435,7 @@ process_input(fd_set *readset)
> 	if (!fderr_eof && FD_ISSET(fderr, readset)) {
> 		errno = 0;
> 		len = read(fderr, buf, sizeof(buf));
>-		if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
>+		if (len < 0 && errno == EINTR) {

similar comment as for channels.c bit: can we use program_terminated
here instead of c->detach close?