Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@xxxxxxxxxxxxxxx.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@xxxxxx

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..60739d861da2 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -36,6 +36,7 @@
 #include <linux/list.h>
 #include <linux/list_sort.h>
 #include <linux/of.h>
+#include <linux/overflow.h>
 
 #include <video/of_display_timing.h>
 #include <video/of_videomode.h>
@@ -1297,8 +1298,10 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode)
 		num *= 2;
 	if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		den *= 2;
-	if (mode->vscan > 1)
-		den *= mode->vscan;
+	if (mode->vscan > 1) {
+		if (unlikely(check_mul_overflow(den, mode->vscan, &den)))
+			return 0;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }