From: Javier Martinez Canillas <javierm@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Maxime Ripard <maxime@cerno.tech>,
Thomas Zimmermann <tzimmermann@suse.de>,
Javier Martinez Canillas <javierm@redhat.com>,
Alex Deucher <alexander.deucher@amd.com>,
Changcheng Deng <deng.changcheng@zte.com.cn>,
Daniel Vetter <daniel@ffwll.ch>, Helge Deller <deller@gmx.de>,
Sam Ravnborg <sam@ravnborg.org>,
Xiyu Yang <xiyuyang19@fudan.edu.cn>,
Zhen Lei <thunder.leizhen@huawei.com>,
dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org
Subject: [PATCH 1/2] fbdev: Check in file_fb_info() if the fb_info was already been freed
Date: Mon, 2 May 2022 15:09:43 +0200 [thread overview]
Message-ID: <20220502130944.363776-2-javierm@redhat.com> (raw)
In-Reply-To: <20220502130944.363776-1-javierm@redhat.com>
If real driver probes, the fbdev core kicks out all drivers that are using
a framebuffer that were provided by the system firmware. But it could be a
user-space process still has a file descriptor for the fbdev device node.
This can lead to a NULL pointer dereference, if the framebuffer device is
unregistered and associated data freed, but later in the .release callback
is attempted to access its struct fb_info.
To prevent this, make file_fb_info() to also check the fb_info reference
counter and just return NULL if this equals zero. Since that means it has
already been freed.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---
drivers/video/fbdev/core/fbmem.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 84427470367b..20d8929df79f 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -751,8 +751,13 @@ static struct fb_info *file_fb_info(struct file *file)
int fbidx = iminor(inode);
struct fb_info *info = registered_fb[fbidx];
- if (info != file->private_data)
- info = NULL;
+ if (!info)
+ return NULL;
+
+ /* check that the fb_info has not changed or was already freed */
+ if (info != file->private_data || refcount_read(&info->count) == 0)
+ return NULL;
+
return info;
}
--
2.35.1
next prev parent reply other threads:[~2022-05-02 13:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-02 13:09 [PATCH 0/2] fbdev: Fix a NULL pointer dereference in fb_release() Javier Martinez Canillas
2022-05-02 13:09 ` Javier Martinez Canillas [this message]
2022-05-02 13:26 ` [PATCH 1/2] fbdev: Check in file_fb_info() if the fb_info was already been freed Thomas Zimmermann
2022-05-02 13:36 ` Javier Martinez Canillas
2022-05-02 13:09 ` [PATCH 2/2] fbdev: Make fb_release() return -ENODEV if fbdev was unregistered Javier Martinez Canillas
2022-05-02 13:20 ` Thomas Zimmermann
2022-05-02 13:39 ` Javier Martinez Canillas
2022-05-04 9:47 ` Daniel Vetter
2022-05-04 10:09 ` Javier Martinez Canillas
2022-05-04 10:15 ` Daniel Vetter
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