[PATCH 2/2] tty: add an option to control logging of passwords with pam_tty_audit

[Richard Guy Briggs]

Most commands are entered one line at a time and processed as complete lines
in non-canonical mode.  Commands that interactively require a password, enter
canonical mode to do this while shutting off echo.  This pair of features
(icanon and !echo) can be used to avoid logging passwords by audit while still
logging the rest of the command.

Adding a member (log_passwd) to the struct audit_tty_status passed in by
pam_tty_audit allows control of canonical mode without echo per task.

Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
 drivers/tty/tty_audit.c    |    9 +++++++++
 include/linux/sched.h      |    1 +
 include/uapi/linux/audit.h |    3 ++-
 kernel/audit.c             |   16 ++++++++++------
 4 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c
index 6953dc8..c5401a6 100644
--- a/drivers/tty/tty_audit.c
+++ b/drivers/tty/tty_audit.c
@@ -153,6 +153,7 @@ void tty_audit_fork(struct signal_struct *sig)
 {
 	spin_lock_irq(&current->sighand->siglock);
 	sig->audit_tty = current->signal->audit_tty;
+	sig->audit_tty_log_passwd = current->signal->audit_tty_log_passwd;
 	spin_unlock_irq(&current->sighand->siglock);
 }
 
@@ -292,10 +293,18 @@ void tty_audit_add_data(struct tty_struct *tty, unsigned char *data,
 {
 	struct tty_audit_buf *buf;
 	int major, minor;
+	int audit_log_tty_passwd;
+	unsigned long flags;
 
 	if (unlikely(size == 0))
 		return;
 
+	spin_lock_irqsave(&current->sighand->siglock, flags);
+	audit_log_tty_passwd = current->signal->audit_tty_log_passwd;
+	spin_unlock_irqrestore(&current->sighand->siglock, flags);
+	if (!audit_log_tty_passwd && icanon && !L_ECHO(tty))
+		return;
+
 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY
 	    && tty->driver->subtype == PTY_TYPE_MASTER)
 		return;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e692a02..d7a5192 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -607,6 +607,7 @@ struct signal_struct {
 #endif
 #ifdef CONFIG_AUDIT
 	unsigned audit_tty;
+	unsigned audit_tty_log_passwd;
 	struct tty_audit_buf *tty_audit_buf;
 #endif
 #ifdef CONFIG_CGROUPS
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 9f096f1..c058c24 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -369,7 +369,8 @@ struct audit_status {
 };
 
 struct audit_tty_status {
-	__u32		enabled; /* 1 = enabled, 0 = disabled */
+	__u32		enabled;	/* 1 = enabled, 0 = disabled */
+	__u32		log_passwd;	/* 1 = enabled, 0 = disabled */
 };
 
 /* audit_rule_data supports filter rules with both integer and string
diff --git a/kernel/audit.c b/kernel/audit.c
index 64354eb..41e4631 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -49,6 +49,7 @@
 #include <linux/slab.h>
 #include <linux/err.h>
 #include <linux/kthread.h>
+#include <linux/kernel.h>
 
 #include <linux/audit.h>
 
@@ -873,6 +874,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 		spin_lock_irq(&tsk->sighand->siglock);
 		s.enabled = tsk->signal->audit_tty;
+		s.log_passwd = tsk->signal->audit_tty_log_passwd;
 		spin_unlock_irq(&tsk->sighand->siglock);
 
 		audit_send_reply(NETLINK_CB(skb).portid, seq,
@@ -880,17 +882,19 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		break;
 	}
 	case AUDIT_TTY_SET: {
-		struct audit_tty_status *s;
+		struct audit_tty_status s;
 		struct task_struct *tsk = current;
 
-		if (nlh->nlmsg_len < sizeof(struct audit_tty_status))
-			return -EINVAL;
-		s = data;
-		if (s->enabled != 0 && s->enabled != 1)
+		memset(&s, 0, sizeof(s));
+		/* guard against past and future API changes */
+		memcpy(&s, data, min(sizeof(s), (size_t)nlh->nlmsg_len));
+		if ((s.enabled != 0 && s.enabled != 1) ||
+		    (s.log_passwd != 0 && s.log_passwd != 1))
 			return -EINVAL;
 
 		spin_lock_irq(&tsk->sighand->siglock);
-		tsk->signal->audit_tty = s->enabled;
+		tsk->signal->audit_tty = s.enabled;
+		tsk->signal->audit_tty_log_passwd = s.log_passwd;
 		spin_unlock_irq(&tsk->sighand->siglock);
 		break;
 	}
-- 
1.7.1