vt: selection, push console lock down

We need to nest the console lock in sel_lock, so we have to push it down
a bit. Fortunately, the callers of set_selection_* just lock the console
lock around the function call. So moving it down is easy.

In the next patch, we switch the order.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Fixes: 07e6124a1a ("vt: selection, close sel_buffer race")
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200228115406.5735-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/selection.c

@@ -51,9 +51,7 @@ static void __speakup_set_selection(struct work_struct *work)
 		goto unref;
 	}
 
-	console_lock();
 	set_selection_kernel(&sel, tty);
-	console_unlock();
 
 unref:
 	tty_kref_put(tty);

drivers/tty/vt/selection.c

@@ -181,7 +181,7 @@ int set_selection_user(const struct tiocl_selection __user *sel,
 	return set_selection_kernel(&v, tty);
 }
 
-int set_selection_kernel(struct tiocl_selection *v, struct tty_struct *tty)
+static int __set_selection_kernel(struct tiocl_selection *v, struct tty_struct *tty)
 {
 	struct vc_data *vc = vc_cons[fg_console].d;
 	int new_sel_start, new_sel_end, spc;
@@ -343,6 +343,17 @@ unlock:
 	mutex_unlock(&sel_lock);
 	return ret;
 }
+
+int set_selection_kernel(struct tiocl_selection *v, struct tty_struct *tty)
+{
+	int ret;
+
+	console_lock();
+	ret = __set_selection_kernel(v, tty);
+	console_unlock();
+
+	return ret;
+}
 EXPORT_SYMBOL_GPL(set_selection_kernel);
 
 /* Insert the contents of the selection buffer into the

drivers/tty/vt/vt.c

@@ -3046,10 +3046,8 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
 	switch (type)
 	{
 		case TIOCL_SETSEL:
-			console_lock();
 			ret = set_selection_user((struct tiocl_selection
 						 __user *)(p+1), tty);
-			console_unlock();
 			break;
 		case TIOCL_PASTESEL:
 			ret = paste_selection(tty);