[PATCH 5/5] fbconsole: reset cursor to origin when changing fonts

[Ahmad Fatoum]

If we switch from one font to another, we update priv->rows and
priv->cols, but priv->x and priv->y remain at their old values.

This becomes problematic, when a bigger font is chosen, because the
coordinates may now exceed the maximum number of rows and lines,
triggering an out-of-bounds memory access, when they are scaled
according to the new font.

Fix this by resetting to (0, 0) whenever the number of columns and rows
changes. The end result looks neater anyway.

Signed-off-by: Ahmad Fatoum <a.fatoum at barebox.org>
---
 drivers/video/fbconsole.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbconsole.c b/drivers/video/fbconsole.c
index 167569abd5c1..fd220a6c1e05 100644
--- a/drivers/video/fbconsole.c
+++ b/drivers/video/fbconsole.c
@@ -679,6 +679,7 @@ static int setup_font(struct fbc_priv *priv)
 	const struct font_desc *font;
 	unsigned int height = priv->fb->yres - priv->margin.top - priv->margin.bottom;
 	unsigned int width = priv->fb->xres - priv->margin.left - priv->margin.right;
+	unsigned int newrows, newcols;
 
 	font = find_font_enum(priv->par_font_val);
 	if (!font) {
@@ -690,14 +691,22 @@ static int setup_font(struct fbc_priv *priv)
 	switch (priv->rotation) {
 	case FBCONSOLE_ROTATE_0:
 	case FBCONSOLE_ROTATE_180:
-		priv->rows = height / priv->font->height;
-		priv->cols = width / priv->font->width;
+		newrows = height / priv->font->height;
+		newcols = width / priv->font->width;
 		break;
 	case FBCONSOLE_ROTATE_90:
 	case FBCONSOLE_ROTATE_270:
-		priv->rows = width / priv->font->height;
-		priv->cols = height / priv->font->width;
+		newrows = width / priv->font->height;
+		newcols = height / priv->font->width;
 		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (priv->rows != newrows || priv->cols != newcols) {
+		priv->rows = newrows;
+		priv->cols = newcols;
+		priv->x = priv->y = 0;
 	}
 
 	return 0;
-- 
2.39.5