linux-kernel - Re: [syzbot] [PATCH] Test divide err in drm

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Message-ID: <000000000000a91e9f060a9488d3@google.com>
Date:   Mon, 20 Nov 2023 04:22:04 -0800
From:   syzbot <syzbot+2e93e6fb36e6fdc56574@...kaller.appspotmail.com>
To:     linux-kernel@...r.kernel.org
Subject: Re: [syzbot] [PATCH] Test divide err in drm

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

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..7c6d0229630d 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>
@@ -1285,7 +1286,7 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, x;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,8 +1298,11 @@ 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)
+	if (mode->vscan > 1) {
+		if (unlikely(check_mul_overflow(den, mode->vscan, &x)))
+			return 0;
 		den *= mode->vscan;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }