linux-kernel - [PATCH 5.17 109/140] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

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Message-Id: <20220510130744.720335167@linuxfoundation.org>
Date:   Tue, 10 May 2022 15:08:19 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxime Ripard <maxime@...no.tech>,
        Junxiao Chang <junxiao.chang@...el.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 109/140] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered

From: Javier Martinez Canillas <javierm@...hat.com>

[ Upstream commit aafa025c76dcc7d1a8c8f0bdefcbe4eb480b2f6a ]

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 registered framebuffer device is for a
driver that just uses a framebuffer provided by the system firmware. In
that case, the fbdev core would unregister the framebuffer device when a
real video driver is probed and ask to remove conflicting framebuffers.

The bug has been present for a long time but commit 27599aacbaef ("fbdev:
Hot-unplug firmware fb devices on forced removal") unmasked it since the
fbdev core started unregistering the framebuffers' devices associated.

Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal")
Reported-by: Maxime Ripard <maxime@...no.tech>
Reported-by: Junxiao Chang <junxiao.chang@...el.com>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220502135014.377945-1-javierm@redhat.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 00f0f282e7a1..10a9369c9dea 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1438,7 +1438,10 @@ 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