Re: [PATCH] fbcon: Check font dimension limits

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On 26. 01. 23, 8:43, Greg KH wrote:
--- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
+++ linux-6.0/drivers/video/fbdev/core/fbcon.c
@@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
  	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
  		return -EINVAL;
+ if (font->width > 32 || font->height > 32)
+		return -EINVAL;
+
  	/* Make sure drawing engine can handle the font */
-	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
-	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
+	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
+	    !(info->pixmap.blit_y & (1U << (font->height - 1))))

Are you sure this is still needed with the above check added?  If so,
why?  What is the difference in the compiled code?

For font->{width,height} == 32, definitely. IMO, 1 << 31 is undefined as 1 << 31 cannot be represented by an (signed) int.

--
js
suse labs




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