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[1/3] fbdev: Prevent possible use-after-free in fb_release()

Message ID 20220504215631.56756-1-javierm@redhat.com (mailing list archive)
State Not Applicable
Headers show
Series fbdev: Fix use-after-free caused by wrong fb_info cleanup in drivers | expand

Commit Message

Javier Martinez Canillas May 4, 2022, 9:56 p.m. UTC 
From: Daniel Vetter <daniel.vetter@ffwll.ch>

Most fbdev drivers have issues with the fb_info lifetime, because call to
framebuffer_release() from their driver's .remove callback, rather than
doing from fbops.fb_destroy callback.

Doing that will destroy the fb_info too early, while references to it may
still exist, leading to a use-after-free error.

To prevent this, check the fb_info reference counter when attempting to
kfree the data structure in framebuffer_release(). That will leak it but
at least will prevent the mentioned error.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 drivers/video/fbdev/core/fbsysfs.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Thomas Zimmermann May 5, 2022, 7:31 a.m. UTC | #1 
Am 04.05.22 um 23:56 schrieb Javier Martinez Canillas:
> From: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Most fbdev drivers have issues with the fb_info lifetime, because call to
> framebuffer_release() from their driver's .remove callback, rather than
> doing from fbops.fb_destroy callback.
> 
> Doing that will destroy the fb_info too early, while references to it may
> still exist, leading to a use-after-free error.
> 
> To prevent this, check the fb_info reference counter when attempting to
> kfree the data structure in framebuffer_release(). That will leak it but
> at least will prevent the mentioned error.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

> ---
> 
>   drivers/video/fbdev/core/fbsysfs.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
> index 26892940c213..82e31a2d845e 100644
> --- a/drivers/video/fbdev/core/fbsysfs.c
> +++ b/drivers/video/fbdev/core/fbsysfs.c
> @@ -80,6 +80,10 @@ void framebuffer_release(struct fb_info *info)
>   {
>   	if (!info)
>   		return;
> +
> +	if (WARN_ON(refcount_read(&info->count)))
> +		return;
> +
>   	kfree(info->apertures);
>   	kfree(info);
>   }
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
index 26892940c213..82e31a2d845e 100644
--- a/drivers/video/fbdev/core/fbsysfs.c
+++ b/drivers/video/fbdev/core/fbsysfs.c
@@ -80,6 +80,10 @@  void framebuffer_release(struct fb_info *info)
 {
 	if (!info)
 		return;
+
+	if (WARN_ON(refcount_read(&info->count)))
+		return;
+
 	kfree(info->apertures);
 	kfree(info);
 }