[PATCH v2 3/4] fbmem: Prevent invalid virtual screen sizes in fb_set_var()

[Helge Deller <deller@gmx.de>]

Prevent that drivers configure a virtual screen resolution smaller than
the physical screen resolution.  This is important, because otherwise we
may access memory outside of the graphics memory area.

Give a kernel WARNing and show the driver name to help locating the buggy
driver.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.4+
---
 drivers/video/fbdev/core/fbmem.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 160389365a36..e8f06d26803c 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1016,6 +1016,18 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 	if (ret)
 		return ret;

+	/* make sure virtual resolution >= physical resolution */
+	if (WARN_ON(var->xres_virtual < var->xres)) {
+		pr_warn("fbcon: Fix up invalid xres %d for %s\n",
+			var->xres_virtual, info->fix.id);
+		var->xres_virtual = var->xres;
+	}
+	if (WARN_ON(var->yres_virtual < var->yres)) {
+		pr_warn("fbcon: Fix up invalid yres %d for %s\n",
+			var->yres_virtual, info->fix.id);
+		var->yres_virtual = var->yres;
+	}
+
 	if ((var->activate & FB_ACTIVATE_MASK) != FB_ACTIVATE_NOW)
 		return 0;

--
2.35.3