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

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Message-ID: <00000000000028ab9d060a6bfcf2@google.com>
Date:   Sat, 18 Nov 2023 03:59:28 -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..539aa26cfc72 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1285,7 +1285,8 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, n1k;
+	int ret;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,9 +1298,17 @@ 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;
+	n1k = mul_u32_u32(num, 1000);
+	if (mode->vscan > 1) {
+		if (den < n1k)
+			den *= mode->vscan;
+	}
+	if (den < n1k)
+		den = n1k + 1;
+	ret = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 
+	printk("mode: %p, ht: %d, vt: %d, c: %d, vsc: %d, den: %ld, num: %ld, n1k: %ld, %d, %s", 
+		mode, mode->htotal, mode->vtotal, mode->clock, mode->vscan, den, num, n1k, ret, __func__);
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);