Staging: speakup: Update __speakup_paste_selection() tty (ab)usage to match vt

commit 28a821c3 upstream.

This function is largely a duplicate of paste_selection() in
drivers/tty/vt/selection.c, but with its own selection state.  The
speakup selection mechanism should really be merged with vt.

For now, apply the changes from 'TTY: vt, fix paste_selection ldisc
handling', 'tty: Make ldisc input flow control concurrency-friendly',
and 'tty: Fix unsafe vt paste_selection()'.

References: https://bugs.debian.org/735202
References: https://bugs.debian.org/744015Reported-by: Paul Gevers <elbrus@debian.org>
Reported-and-tested-by: Jarek Czekalski <jarekczek@poczta.onet.pl>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[bwh: Backported to 3.10:
 - Only apply the changes from 'TTY: vt, fix paste_selection ldisc handling'
 - Add the same FIXME comment as vt's paste_selection() has in this version]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/selection.c

@@ -5,6 +5,7 @@
 #include <linux/device.h> /* for dev_warn */
 #include <linux/selection.h>
 #include <linux/workqueue.h>
+#include <linux/tty.h>
 #include <asm/cmpxchg.h>
 
 #include "speakup.h"
@@ -135,8 +136,12 @@ static void __speakup_paste_selection(struct work_struct *work)
 	struct tty_struct *tty = xchg(&spw->tty, NULL);
 	struct vc_data *vc = (struct vc_data *) tty->driver_data;
 	int pasted = 0, count;
+	struct tty_ldisc *ld;
 	DECLARE_WAITQUEUE(wait, current);
 
+	ld = tty_ldisc_ref_wait(tty);
+
+	/* FIXME: this is completely unsafe */
 	add_wait_queue(&vc->paste_wait, &wait);
 	while (sel_buffer && sel_buffer_lth > pasted) {
 		set_current_state(TASK_INTERRUPTIBLE);
@@ -146,12 +151,13 @@ static void __speakup_paste_selection(struct work_struct *work)
 		}
 		count = sel_buffer_lth - pasted;
 		count = min_t(int, count, tty->receive_room);
-		tty->ldisc->ops->receive_buf(tty, sel_buffer + pasted,
-			NULL, count);
+		ld->ops->receive_buf(tty, sel_buffer + pasted, NULL, count);
 		pasted += count;
 	}
 	remove_wait_queue(&vc->paste_wait, &wait);
 	current->state = TASK_RUNNING;
+
+	tty_ldisc_deref(ld);
 	tty_kref_put(tty);
 }