[kbd] [PATCH] vlock: Handle tty dying

[Kyle Manna <kyle@kylemanna.com>]

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Hi guys,

I ran into a problem where if vlock was running over ssh and the ssh
session died my system logs would get spammed by the now orphaned vlock
process on Arch Linux:

    Sep 25 20:51:12 hostname vlock[31336]: pam_unix(vlock:auth): auth could not identify password for [user]
    Sep 25 20:51:13 hostname vlock[31336]: pam_unix(vlock:auth): auth could not identify password for [user]
    Sep 25 20:51:14 hostname vlock[31336]: pam_unix(vlock:auth): auth could not identify password for [user]

I was able to re-create this in many other situations (ssh, xterm
window/tab, tmux window/pane, etc).

The patch know checks for a tty on stdin where PAM will likely ask for
the password and exits if it's not found.


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From ec97bfb838ff45a1f7c3a640cb29f7eeb2718db3 Mon Sep 17 00:00:00 2001
From: Kyle Manna <kyle@kylemanna.com>
Date: Thu, 25 Sep 2014 22:22:17 -0700
Subject: [PATCH] vlock: Handle tty dying

* Gracefully exit when the parent tty dies.
* Typical causes of death include closing:
    * terminal tab or window
    * shell
    * ssh session
* If no tty exists, I'm not sure what vlock would be locking.

Signed-off-by: Kyle Manna <kyle@kylemanna.com>
---
 src/vlock/auth.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/vlock/auth.c b/src/vlock/auth.c
index da135ce..79b1319 100644
--- a/src/vlock/auth.c
+++ b/src/vlock/auth.c
@@ -67,6 +67,17 @@ get_password (pam_handle_t * pamh, const char *username, const char *tty)
 		int     rc;
 		const char *msg;
 
+		/* Ensure that the process has a tty.  If the parent had died,
+		 * stdin/out are likely no longer valid and PAM will fail continuously.
+		 */
+		if (isatty(STDIN_FILENO) != 1)
+		{
+			syslog (LOG_INFO,
+				"TTY %s disappeared for %s by (uid=%u)",
+				tty, username, uid);
+			return EXIT_FAILURE;
+		}
+
 		if (!pamh)
 		{
 			pamh = init_pam (username, tty, 1);
-- 
2.1.1