linux-kernel - [PATCH v2] drm/fb-helper: add virtual screen size check to drm_fb_helper_check

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Date:   Thu, 11 Aug 2022 17:48:50 +0300
From:   Andrey Strachuk <strochuk@...ras.ru>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Andrey Strachuk <strochuk@...ras.ru>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Helge Deller <deller@....de>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org
Subject: [PATCH v2] drm/fb-helper: add virtual screen size check to drm_fb_helper_check_var()

Add virtual screen size check to drm_fb_helper_check_var() in
order to validate userspace input.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Signed-off-by: Andrey Strachuk <strochuk@...ras.ru>
Fixes: 785b93ef8c30 ("drm/kms: move driver specific fb common code to helper functions (v2)")
---
 drivers/gpu/drm/drm_fb_helper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 2d4cee6a10ff..5c8b211769eb 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1355,6 +1355,12 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 	    (drm_format_info_block_height(fb->format, 0) > 1))
 		return -EINVAL;
 
+	/* verify that virtual resolution >= physical resolution */
+	if (var->xres_virtual < var->xres)
+		var->xres_virtual = var->xres;
+	if (var->yres_virtual < var->yres)
+		var->yres_virtual = var->yres;
+
 	/*
 	 * Changes struct fb_var_screeninfo are currently not pushed back
 	 * to KMS, hence fail if different settings are requested.
-- 
2.25.1