tty: audit: Ignore current association for audit push

In canonical read mode, each line read and logged is pushed separately
with tty_audit_push(). For all single-threaded processes and multi-threaded
processes reading from only one tty, this patch has no effect; the last line
read will still be the entry pushed to the audit log because the tty
association cannot have changed between tty_audit_add_data() and
tty_audit_push().

For multi-threaded processes reading from different ttys concurrently,
the audit log will have mixed log entries anyway. Consider two ttys
audited concurrently:

CPU0                           CPU1
----------                     ------------
tty_audit_add_data(ttyA)
                               tty_audit_add_data(ttyB)
tty_audit_push()
                               tty_audit_add_data(ttyB)
                               tty_audit_push()

This patch will now cause the ttyB output to be split into separate
audit log entries.

However, this possibility is equally likely without this patch:

CPU0                           CPU1
----------                     ------------
                               tty_audit_add_data(ttyB)
tty_audit_add_data(ttyA)
tty_audit_push()
                               tty_audit_add_data(ttyB)
                               tty_audit_push()

Mixed canonical and non-canonical reads have similar races.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -2072,7 +2072,7 @@ static int canon_copy_from_read_buf(struct tty_struct *tty,
 			ldata->line_start = ldata->read_tail;
 		else
 			ldata->push = 0;
-		tty_audit_push(tty);
+		tty_audit_push();
 	}
 	return 0;
 }

drivers/tty/tty_audit.c

@@ -313,9 +313,9 @@ void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
 /**
  *	tty_audit_push	-	Push buffered data out
  *
- *	Make sure no audit data is pending for @tty on the current process.
+ *	Make sure no audit data is pending on the current process.
  */
-void tty_audit_push(struct tty_struct *tty)
+void tty_audit_push(void)
 {
 	struct tty_audit_buf *buf;
 	unsigned long flags;
@@ -331,13 +331,8 @@ void tty_audit_push(struct tty_struct *tty)
 	spin_unlock_irqrestore(&current->sighand->siglock, flags);
 
 	if (buf) {
-		int major, minor;
-
-		major = tty->driver->major;
-		minor = tty->driver->minor_start + tty->index;
 		mutex_lock(&buf->mutex);
-		if (buf->major == major && buf->minor == minor)
-			tty_audit_buf_push(buf);
+		tty_audit_buf_push(buf);
 		mutex_unlock(&buf->mutex);
 		tty_audit_buf_put(buf);
 	}

include/linux/tty.h

@@ -597,7 +597,7 @@ extern void tty_audit_add_data(struct tty_struct *tty, const void *data,
 extern void tty_audit_exit(void);
 extern void tty_audit_fork(struct signal_struct *sig);
 extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
-extern void tty_audit_push(struct tty_struct *tty);
+extern void tty_audit_push(void);
 extern int tty_audit_push_current(void);
 #else
 static inline void tty_audit_add_data(struct tty_struct *tty, const void *data,
@@ -613,7 +613,7 @@ static inline void tty_audit_exit(void)
 static inline void tty_audit_fork(struct signal_struct *sig)
 {
 }
-static inline void tty_audit_push(struct tty_struct *tty)
+static inline void tty_audit_push(void)
 {
 }
 static inline int tty_audit_push_current(void)