diff -up openssh-8.6p1/channels.c.restore-nonblock openssh-8.6p1/channels.c

--- openssh-8.6p1/channels.c.restore-nonblock	2021-05-10 10:55:46.981156096 +0200

+++ openssh-8.6p1/channels.c	2021-05-10 11:05:14.674641053 +0200

@@ -298,32 +298,38 @@ channel_lookup(struct ssh *ssh, int id)

 }

 /*

- * Register filedescriptors for a channel, used when allocating a channel or

- * when the channel consumer/producer is ready, e.g. shell exec'd

+ * Register a filedescriptor.

  */

 static void

-channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,

-    int extusage, int nonblock, int is_tty)

+channel_register_fd(struct ssh *ssh, int fd, int nonblock)

 {

 	struct ssh_channels *sc = ssh->chanctxt;

 	/* Update the maximum file descriptor value. */

-	sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, rfd);

-	sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, wfd);

-	sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, efd);

-

-	if (rfd != -1)

-		fcntl(rfd, F_SETFD, FD_CLOEXEC);

-	if (wfd != -1 && wfd != rfd)

-		fcntl(wfd, F_SETFD, FD_CLOEXEC);

-	if (efd != -1 && efd != rfd && efd != wfd)

-		fcntl(efd, F_SETFD, FD_CLOEXEC);

+	sc->channel_max_fd = MAXIMUM(sc->channel_max_fd, fd);

+

+	if (fd != -1)

+		fcntl(fd, F_SETFD, FD_CLOEXEC);

+	/* enable nonblocking mode */

+	if (nonblock && fd != -1 && !isatty(fd))

+		set_nonblock(fd);

+}

+

+/*

+ * Register filedescriptors for a channel, used when allocating a channel or

+ * when the channel consumer/producer is ready, e.g. shell exec'd

+ */

+static void

+channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,

+    int extusage, int nonblock, int is_tty)

+{

 	c->rfd = rfd;

 	c->wfd = wfd;

 	c->sock = (rfd == wfd) ? rfd : -1;

 	c->efd = efd;

 	c->extended_usage = extusage;

+	c->nonblock = 0;

 	if ((c->isatty = is_tty) != 0)

 		debug2("channel %d: rfd %d isatty", c->self, c->rfd);

@@ -332,14 +338,20 @@ channel_register_fds(struct ssh *ssh, Ch

 	c->wfd_isatty = is_tty || isatty(c->wfd);

 #endif

-	/* enable nonblocking mode */

-	if (nonblock) {

-		if (rfd != -1)

-			set_nonblock(rfd);

-		if (wfd != -1)

-			set_nonblock(wfd);

-		if (efd != -1)

-			set_nonblock(efd);

+	if (rfd != -1) {

+		if ((fcntl(rfd, F_GETFL) & O_NONBLOCK) == 0)

+			c->nonblock |= NEED_RESTORE_STDIN_NONBLOCK;

+		channel_register_fd(ssh, rfd, nonblock);

+	}

+	if (wfd != -1 && wfd != rfd) {

+		if ((fcntl(wfd, F_GETFL) & O_NONBLOCK) == 0)

+			c->nonblock |= NEED_RESTORE_STDOUT_NONBLOCK;

+		channel_register_fd(ssh, wfd, nonblock);

+	}

+	if (efd != -1 && efd != rfd && efd != wfd) {

+		if ((fcntl(efd, F_GETFL) & O_NONBLOCK) == 0)

+			c->nonblock |= NEED_RESTORE_STDERR_NONBLOCK;

+		channel_register_fd(ssh, efd, nonblock);

 	}

 }

@@ -422,11 +434,15 @@ channel_find_maxfd(struct ssh_channels *

 }

 int

-channel_close_fd(struct ssh *ssh, int *fdp)

+channel_close_fd(struct ssh *ssh, int *fdp, int nonblock)

 {

 	struct ssh_channels *sc = ssh->chanctxt;

 	int ret = 0, fd = *fdp;

+	/* As the fd is duped, restoring the block mode

+	 * affects the original fd */

+	if (nonblock && fd != -1 && !isatty(fd))

+		unset_nonblock(fd);

 	if (fd != -1) {

 		ret = close(fd);

 		*fdp = -1;

@@ -442,13 +458,13 @@ channel_close_fds(struct ssh *ssh, Chann

 {

 	int sock = c->sock, rfd = c->rfd, wfd = c->wfd, efd = c->efd;

-	channel_close_fd(ssh, &c->sock);

+	channel_close_fd(ssh, &c->sock, 0);

 	if (rfd != sock)

-		channel_close_fd(ssh, &c->rfd);

+		channel_close_fd(ssh, &c->rfd, c->nonblock & NEED_RESTORE_STDIN_NONBLOCK);

 	if (wfd != sock && wfd != rfd)

-		channel_close_fd(ssh, &c->wfd);

+		channel_close_fd(ssh, &c->wfd, c->nonblock & NEED_RESTORE_STDOUT_NONBLOCK);

 	if (efd != sock && efd != rfd && efd != wfd)

-		channel_close_fd(ssh, &c->efd);

+		channel_close_fd(ssh, &c->efd, c->nonblock & NEED_RESTORE_STDERR_NONBLOCK);

 }

 static void

@@ -702,7 +718,7 @@ channel_stop_listening(struct ssh *ssh)

 			case SSH_CHANNEL_X11_LISTENER:

 			case SSH_CHANNEL_UNIX_LISTENER:

 			case SSH_CHANNEL_RUNIX_LISTENER:

-				channel_close_fd(ssh, &c->sock);

+				channel_close_fd(ssh, &c->sock, 0);

 				channel_free(ssh, c);

 				break;

 			}

@@ -1649,7 +1665,7 @@ channel_post_x11_listener(struct ssh *ss

 	if (c->single_connection) {

 		oerrno = errno;

 		debug2("single_connection: closing X11 listener.");

-		channel_close_fd(ssh, &c->sock);

+		channel_close_fd(ssh, &c->sock, 0);

 		chan_mark_dead(ssh, c);

 		errno = oerrno;

 	}

@@ -2058,7 +2074,7 @@ channel_handle_efd_write(struct ssh *ssh

 		return 1;

 	if (len <= 0) {

 		debug2("channel %d: closing write-efd %d", c->self, c->efd);

-		channel_close_fd(ssh, &c->efd);

+		channel_close_fd(ssh, &c->efd, c->nonblock & NEED_RESTORE_STDERR_NONBLOCK);

 	} else {

 		if ((r = sshbuf_consume(c->extended, len)) != 0)

 			fatal_fr(r, "channel %i: consume", c->self);

@@ -2087,7 +2103,7 @@ channel_handle_efd_read(struct ssh *ssh,

 		return 1;

 	if (len <= 0) {

 		debug2("channel %d: closing read-efd %d", c->self, c->efd);

-		channel_close_fd(ssh, &c->efd);

+		channel_close_fd(ssh, &c->efd, c->nonblock & NEED_RESTORE_STDERR_NONBLOCK);

 	} else if (c->extended_usage == CHAN_EXTENDED_IGNORE)

 		debug3("channel %d: discard efd", c->self);

 	else if ((r = sshbuf_put(c->extended, buf, len)) != 0)

diff -up openssh-8.6p1/channels.h.restore-nonblock openssh-8.6p1/channels.h

--- openssh-8.6p1/channels.h.restore-nonblock	2021-05-10 10:55:46.942155788 +0200

+++ openssh-8.6p1/channels.h	2021-05-10 11:01:41.123953937 +0200

@@ -188,8 +188,15 @@ struct Channel {

 	void			*mux_ctx;

 	int			mux_pause;

 	int			mux_downstream_id;

+

+	/* whether non-blocking is set to descriptors */

+	int 			nonblock;

 };

+#define NEED_RESTORE_STDIN_NONBLOCK  1

+#define NEED_RESTORE_STDOUT_NONBLOCK 2

+#define NEED_RESTORE_STDERR_NONBLOCK 4

+

 #define CHAN_EXTENDED_IGNORE		0

 #define CHAN_EXTENDED_READ		1

 #define CHAN_EXTENDED_WRITE		2

@@ -266,7 +273,7 @@ void	 channel_register_filter(struct ssh

 void	 channel_register_status_confirm(struct ssh *, int,

 	    channel_confirm_cb *, channel_confirm_abandon_cb *, void *);

 void	 channel_cancel_cleanup(struct ssh *, int);

-int	 channel_close_fd(struct ssh *, int *);

+int	 channel_close_fd(struct ssh *, int *, int);

 void	 channel_send_window_changes(struct ssh *);

 /* mux proxy support */

diff -up openssh-8.6p1/nchan.c.restore-nonblock openssh-8.6p1/nchan.c

--- openssh-8.6p1/nchan.c.restore-nonblock	2021-05-10 10:55:46.990156168 +0200

+++ openssh-8.6p1/nchan.c	2021-05-10 11:03:46.679945863 +0200

@@ -384,7 +384,7 @@ chan_shutdown_write(struct ssh *ssh, Cha

 			    c->istate, c->ostate, strerror(errno));

 		}

 	} else {

-		if (channel_close_fd(ssh, &c->wfd) < 0) {

+		if (channel_close_fd(ssh, &c->wfd, c->nonblock & NEED_RESTORE_STDOUT_NONBLOCK) < 0) {

 			logit_f("channel %d: close() failed for "

 			    "fd %d [i%d o%d]: %.100s", c->self, c->wfd,

 			    c->istate, c->ostate, strerror(errno));

@@ -412,7 +412,7 @@ chan_shutdown_read(struct ssh *ssh, Chan

 			    c->istate, c->ostate, strerror(errno));

 		}

 	} else {

-		if (channel_close_fd(ssh, &c->rfd) < 0) {

+		if (channel_close_fd(ssh, &c->rfd, c->nonblock & NEED_RESTORE_STDIN_NONBLOCK) < 0) {

 			logit_f("channel %d: close() failed for "

 			    "fd %d [i%d o%d]: %.100s", c->self, c->rfd,

 			    c->istate, c->ostate, strerror(errno));

@@ -431,7 +431,7 @@ chan_shutdown_extended_read(struct ssh *

 	debug_f("channel %d: (i%d o%d sock %d wfd %d efd %d [%s])",

 	    c->self, c->istate, c->ostate, c->sock, c->rfd, c->efd,

 	    channel_format_extended_usage(c));

-	if (channel_close_fd(ssh, &c->efd) < 0) {

+	if (channel_close_fd(ssh, &c->efd, c->nonblock & NEED_RESTORE_STDERR_NONBLOCK) < 0) {

 		logit_f("channel %d: close() failed for "

 		    "extended fd %d [i%d o%d]: %.100s", c->self, c->efd,

 		    c->istate, c->ostate, strerror(errno));

diff -up openssh-8.6p1/ssh.c.restore-nonblock openssh-8.6p1/ssh.c

--- openssh-8.6p1/ssh.c.restore-nonblock	2021-05-10 10:55:46.991156175 +0200

+++ openssh-8.6p1/ssh.c	2021-05-10 11:06:28.315222828 +0200

@@ -2085,14 +2085,6 @@ ssh_session2_open(struct ssh *ssh)

 	if (in == -1 || out == -1 || err == -1)

 		fatal("dup() in/out/err failed");

-	/* enable nonblocking unless tty */

-	if (!isatty(in))

-		set_nonblock(in);

-	if (!isatty(out))

-		set_nonblock(out);

-	if (!isatty(err))

-		set_nonblock(err);

-

 	window = CHAN_SES_WINDOW_DEFAULT;

 	packetmax = CHAN_SES_PACKET_DEFAULT;

 	if (tty_flag) {

@@ -2102,7 +2094,7 @@ ssh_session2_open(struct ssh *ssh)

 	c = channel_new(ssh,

 	    "session", SSH_CHANNEL_OPENING, in, out, err,

 	    window, packetmax, CHAN_EXTENDED_WRITE,

-	    "client-session", /*nonblock*/0);

+	    "client-session", /*nonblock*/1);

 	debug3_f("channel_new: %d", c->self);