[PATCH 4/5] fbmem: Prevent invalid virtual screen sizes in fb_set_var()

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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.

Signed-off-by: Helge Deller <deller@xxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.4+
---
 drivers/video/fbdev/core/fbmem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 324f726739c4..222d94e2e0a2 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1006,6 +1006,12 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 	if (var->xres < 8 || var->yres < 8)
 		return -EINVAL;

+	/* make sure virtual resolution >= physical resolution */
+	if (WARN_ON(var->xres_virtual < var->xres))
+		var->xres_virtual = var->xres;
+	if (WARN_ON(var->yres_virtual < var->yres))
+		var->yres_virtual = var->yres;
+
 	/* Too huge resolution causes multiplication overflow. */
 	if (check_mul_overflow(var->xres, var->yres, &unused) ||
 	    check_mul_overflow(var->xres_virtual, var->yres_virtual, &unused))
--
2.35.3




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