allow some additional control over the use of ssh-askpass

via $SSH_ASKPASS_REQUIRE, including force-enable/disable.
bz#69 ok markus@

4 files changed, 70 insertions, 15 deletions

diff --git a/usr.bin/ssh/readpass.c b/usr.bin/ssh/readpass.c
index 104c3188ddb..1df058e45ff 100644
--- a/usr.bin/ssh/readpass.c
+++ b/usr.bin/ssh/readpass.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readpass.c,v 1.61 2020/01/23 07:10:22 dtucker Exp $ */
+/* $OpenBSD: readpass.c,v 1.62 2020/07/14 23:57:01 djm Exp $ */
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
  *
@@ -120,11 +120,26 @@ char *
 read_passphrase(const char *prompt, int flags)
 {
 	char cr = '\r', *askpass = NULL, *ret, buf[1024];
-	int rppflags, use_askpass = 0, ttyfd;
+	int rppflags, ttyfd, use_askpass = 0, allow_askpass = 0;
 	const char *askpass_hint = NULL;
+	const char *s;
+
+	if ((s = getenv("DISPLAY")) != NULL)
+		allow_askpass = *s != '\0';
+	if ((s = getenv(SSH_ASKPASS_REQUIRE_ENV)) != NULL) {
+		if (strcasecmp(s, "force") == 0) {
+			use_askpass = 1;
+			allow_askpass = 1;
+		} else if (strcasecmp(s, "prefer") == 0)
+			use_askpass = allow_askpass;
+		else if (strcasecmp(s, "never") == 0)
+			allow_askpass = 0;
+	}
 
 	rppflags = (flags & RP_ECHO) ? RPP_ECHO_ON : RPP_ECHO_OFF;
-	if (flags & RP_USE_ASKPASS)
+	if (use_askpass)
+		debug("%s: requested to askpass", __func__);
+	else if (flags & RP_USE_ASKPASS)
 		use_askpass = 1;
 	else if (flags & RP_ALLOW_STDIN) {
 		if (!isatty(STDIN_FILENO)) {
@@ -150,10 +165,10 @@ read_passphrase(const char *prompt, int flags)
 		}
 	}
 
-	if ((flags & RP_USE_ASKPASS) && getenv("DISPLAY") == NULL)
+	if ((flags & RP_USE_ASKPASS) && !allow_askpass)
 		return (flags & RP_ALLOW_EOF) ? NULL : xstrdup("");
 
-	if (use_askpass && getenv("DISPLAY")) {
+	if (use_askpass && allow_askpass) {
 		if (getenv(SSH_ASKPASS_ENV))
 			askpass = getenv(SSH_ASKPASS_ENV);
 		else
diff --git a/usr.bin/ssh/ssh-add.1 b/usr.bin/ssh/ssh-add.1
index f3db1956e1b..2786df51417 100644
--- a/usr.bin/ssh/ssh-add.1
+++ b/usr.bin/ssh/ssh-add.1
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-add.1,v 1.80 2020/06/26 05:04:07 djm Exp $
+.\"	$OpenBSD: ssh-add.1,v 1.81 2020/07/14 23:57:01 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -35,7 +35,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: June 26 2020 $
+.Dd $Mdocdate: July 14 2020 $
 .Dt SSH-ADD 1
 .Os
 .Sh NAME
@@ -174,7 +174,7 @@ Lock the agent with a password.
 .El
 .Sh ENVIRONMENT
 .Bl -tag -width Ds
-.It Ev "DISPLAY" and "SSH_ASKPASS"
+.It Ev "DISPLAY", "SSH_ASKPASS" and "SSH_ASKPASS_REQUIRE"
 If
 .Nm
 needs a passphrase, it will read the passphrase from the current
@@ -195,10 +195,26 @@ This is particularly useful when calling
 from a
 .Pa .xsession
 or related script.
-(Note that on some machines it
-may be necessary to redirect the input from
-.Pa /dev/null
-to make this work.)
+.Pp
+.Ev SSH_ASKPASS_REQUIRE
+allows further control over the use of an askpass program.
+If this variable is set to
+.Dq never
+then
+.Nm
+will never attempt to use one.
+If it is set to
+.Dq prefer ,
+then
+.Nm
+will prefer to use the askpass program instead of the TTY when requesting
+passwords.
+Finally, if the variable is set to
+.Dq force ,
+then the askpass program will be used for all passphrase input regardless
+of whether
+.Ev DISPLAY
+is set.
 .It Ev SSH_AUTH_SOCK
 Identifies the path of a
 .Ux Ns -domain
diff --git a/usr.bin/ssh/ssh.1 b/usr.bin/ssh/ssh.1
index dce5f404b3a..7b9d3422b58 100644
--- a/usr.bin/ssh/ssh.1
+++ b/usr.bin/ssh/ssh.1
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh.1,v 1.412 2020/04/17 03:34:42 djm Exp $
-.Dd $Mdocdate: April 17 2020 $
+.\" $OpenBSD: ssh.1,v 1.413 2020/07/14 23:57:01 djm Exp $
+.Dd $Mdocdate: July 14 2020 $
 .Dt SSH 1
 .Os
 .Sh NAME
@@ -1409,6 +1409,25 @@ or related script.
 may be necessary to redirect the input from
 .Pa /dev/null
 to make this work.)
+.It Ev SSH_ASKPASS_REQUIRE
+allows further control over the use of an askpass program.
+If this variable is set to
+.Dq never
+then
+.Nm
+will never attempt to use one.
+If it is set to
+.Dq prefer ,
+then
+.Nm
+will prefer to use the askpass program instead of the TTY when requesting
+passwords.
+Finally, if the variable is set to
+.Dq force ,
+then the askpass program will be used for all passphrase input regardless
+of whether
+.Ev DISPLAY
+is set.
 .It Ev SSH_AUTH_SOCK
 Identifies the path of a
 .Ux Ns -domain
diff --git a/usr.bin/ssh/ssh.h b/usr.bin/ssh/ssh.h
index 0d1080bbfbe..e40f04aa3a5 100644
--- a/usr.bin/ssh/ssh.h
+++ b/usr.bin/ssh/ssh.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.h,v 1.89 2018/12/27 03:25:25 djm Exp $ */
+/* $OpenBSD: ssh.h,v 1.90 2020/07/14 23:57:01 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -68,6 +68,11 @@
 #define SSH_ASKPASS_ENV		"SSH_ASKPASS"
 
 /*
+ * Environment variable to control whether or not askpass is used.
+ */
+#define SSH_ASKPASS_REQUIRE_ENV		"SSH_ASKPASS_REQUIRE"
+
+/*
  * Force host key length and server key length to differ by at least this
  * many bits.  This is to make double encryption with rsaref work.
  */