[PATCH v3 3/4] fbmem: Check virtual screen sizes in fb_set_var()

[Helge Deller <deller@gmx.de>]

Verify that the fbdev or drm driver correctly adjusted the virtual
screen sizes. On failure report the failing driver and reject the screen
size change.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.4+
---
 drivers/video/fbdev/core/fbmem.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 160389365a36..612b54c23ac7 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1016,6 +1016,17 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 	if (ret)
 		return ret;

+	/* verify that virtual resolution >= physical resolution */
+	if (var->xres_virtual < var->xres ||
+	    var->yres_virtual < var->yres) {
+		pr_warn("WARNING: fbcon: Driver '%s' missed to adjust virtual"
+			" screen size (%dx%d vs. %dx%d)\n",
+			info->fix.id,
+			var->xres_virtual, var->yres_virtual,
+			var->xres, var->yres);
+		return -EINVAL;
+	}
+
 	if ((var->activate & FB_ACTIVATE_MASK) != FB_ACTIVATE_NOW)
 		return 0;

--
2.35.3