Re: [PATCH] drm/fbdev-generic: fix potential out-of-bounds access

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Hi

Am 13.04.23 um 20:56 schrieb Daniel Vetter:
[...]

This should switch the existing code over to using drm_framebuffer instead
of fbdev:


diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index ef4eb8b12766..99ca69dd432f 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -647,22 +647,26 @@ static void drm_fb_helper_damage(struct drm_fb_helper *helper, u32 x, u32 y,
  static void drm_fb_helper_memory_range_to_clip(struct fb_info *info, off_t off, size_t len,
  					       struct drm_rect *clip)
  {
+	struct drm_fb_helper *helper = info->par;
+
  	off_t end = off + len;
  	u32 x1 = 0;
  	u32 y1 = off / info->fix.line_length;
-	u32 x2 = info->var.xres;
-	u32 y2 = DIV_ROUND_UP(end, info->fix.line_length);
+	u32 x2 = helper->fb->height;
+	unsigned stride = helper->fb->pitches[0];
+	u32 y2 = DIV_ROUND_UP(end, stride);
+	int bpp = drm_format_info_bpp(helper->fb->format, 0);

Please DONT do that. The code here is fbdev code and shouldn't bother about DRM data structures. Actually, it shouldn't be here: a number of fbdev drivers with deferred I/O contain similar code and the fbdev module should provide us with a helper. (I think I even had some patches somewhere.)

Best regards
Thomas

if ((y2 - y1) == 1) {
  		/*
  		 * We've only written to a single scanline. Try to reduce
  		 * the number of horizontal pixels that need an update.
  		 */
-		off_t bit_off = (off % info->fix.line_length) * 8;
-		off_t bit_end = (end % info->fix.line_length) * 8;
+		off_t bit_off = (off % stride) * 8;
+		off_t bit_end = (end % stride) * 8;
- x1 = bit_off / info->var.bits_per_pixel;
-		x2 = DIV_ROUND_UP(bit_end, info->var.bits_per_pixel);
+		x1 = bit_off / bpp;
+		x2 = DIV_ROUND_UP(bit_end, bpp);
  	}
drm_rect_init(clip, x1, y1, x2 - x1, y2 - y1);


+  screen_size = sizes->surface_height * buffer->fb->pitches[0];
+
             screen_buffer = vzalloc(screen_size);
             if (!screen_buffer) {
                     ret = -ENOMEM;
Cheers, Daniel

--
2.25.1





--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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