linux-kernel - [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

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Message-Id: <20220502130944.363776-3-javierm@redhat.com>
Date:   Mon,  2 May 2022 15:09:44 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Maxime Ripard <maxime@...no.tech>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Daniel Vetter <daniel@...ll.ch>,
        Guenter Roeck <linux@...ck-us.net>,
        Helge Deller <deller@....de>, Sam Ravnborg <sam@...nborg.org>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Zheyu Ma <zheyuma97@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

A reference to the framebuffer device struct fb_info is stored in the file
private data, but this reference could no longer be valid and must not be
accessed directly. Instead, the file_fb_info() accessor function must be
used since it does sanity checking to make sure that the fb_info is valid.

This can happen for example if the fbdev driver was one that is using a
framebuffer provided by the system firmware. In that case, the fbdev core
could unregister the framebuffer device if a real video driver is probed.

Reported-by: Maxime Ripard <maxime@...no.tech>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
---

 drivers/video/fbdev/core/fbmem.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 20d8929df79f..d68097105f93 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1439,7 +1439,10 @@ fb_release(struct inode *inode, struct file *file)
 __acquires(&info->lock)
 __releases(&info->lock)
 {
-	struct fb_info * const info = file->private_data;
+	struct fb_info * const info = file_fb_info(file);
+
+	if (!info)
+		return -ENODEV;
 
 	lock_fb_info(info);
 	if (info->fbops->fb_release)
-- 
2.35.1