linux-kernel - [PATCH] drm/fb-helper: Fix height, width, and accel_flags in fb

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Message-Id: <2b6073d9c2d869c6a4eac6edebd616e0568dec91.1681843245.git.geert+renesas@glider.be>
Date:   Tue, 18 Apr 2023 20:42:46 +0200
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Javier Martinez Canillas <javierm@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] drm/fb-helper: Fix height, width, and accel_flags in fb_var

Fbtest contains some very simple validation of the fbdev userspace API
contract.  When used with shmob-drm, it reports the following warnings
and errors:

    height changed from 68 to 0
    height was rounded down
    width changed from 111 to 0
    width was rounded down
    accel_flags changed from 0 to 1

The first part happens because __fill_var() resets the physical
dimensions of the first connector, as filled in by drm_setup_crtcs_fb().
Fix this by retaining the original values.

The last part happens because __fill_var() forces the FB_ACCELF_TEXT
flag on, while fbtest disables all acceleration on purpose, so it can
draw safely to the frame buffer.  Fix this by setting accel_flags to
zero, as DRM does not implement any text console acceleration.
Note that this issue can also be seen in the output of fbset, which
reports "accel true".

Fixes: ee4cce0a8f03a333 ("drm/fb-helper: fix input validation gaps in check_var")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 drivers/gpu/drm/drm_fb_helper.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 64458982be40c468..ed6ad787915f0b8f 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1537,17 +1537,19 @@ static void drm_fb_helper_fill_pixel_fmt(struct fb_var_screeninfo *var,
 	}
 }
 
-static void __fill_var(struct fb_var_screeninfo *var,
+static void __fill_var(struct fb_var_screeninfo *var, struct fb_info *info,
 		       struct drm_framebuffer *fb)
 {
 	int i;
 
 	var->xres_virtual = fb->width;
 	var->yres_virtual = fb->height;
-	var->accel_flags = FB_ACCELF_TEXT;
+	var->accel_flags = 0;
 	var->bits_per_pixel = drm_format_info_bpp(fb->format, 0);
 
-	var->height = var->width = 0;
+	var->height = info->var.height;
+	var->width = info->var.width;
+
 	var->left_margin = var->right_margin = 0;
 	var->upper_margin = var->lower_margin = 0;
 	var->hsync_len = var->vsync_len = 0;
@@ -1610,7 +1612,7 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 		return -EINVAL;
 	}
 
-	__fill_var(var, fb);
+	__fill_var(var, info, fb);
 
 	/*
 	 * fb_pan_display() validates this, but fb_set_par() doesn't and just
@@ -2066,7 +2068,7 @@ static void drm_fb_helper_fill_var(struct fb_info *info,
 	info->pseudo_palette = fb_helper->pseudo_palette;
 	info->var.xoffset = 0;
 	info->var.yoffset = 0;
-	__fill_var(&info->var, fb);
+	__fill_var(&info->var, info, fb);
 	info->var.activate = FB_ACTIVATE_NOW;
 
 	drm_fb_helper_fill_pixel_fmt(&info->var, format);
-- 
2.34.1