[PATCH] fbdev: Fix invalid page access after closing deferred I/O devices

[Patrik Jakobsson]

On Fri, Jan 27, 2023 at 05:58:34PM +0100, Takashi Iwai wrote:
> When a fbdev with deferred I/O is once opened and closed, the dirty
> pages still remain queued in the pageref list, and eventually later
> those may be processed in the delayed work.  This may lead to a
> corruption of pages, hitting an Oops.
> 
> This patch makes sure to cancel the delayed work and clean up the
> pageref list at closing the device for addressing the bug.  A part of
> the cleanup code is factored out as a new helper function that is
> called from the common fb_release().
> 
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>

Reviewed-by: Patrik Jakobsson <pjakobsson at suse.de>

> ---
>  drivers/video/fbdev/core/fb_defio.c | 10 +++++++++-
>  drivers/video/fbdev/core/fbmem.c    |  2 ++
>  include/linux/fb.h                  |  1 +
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
> index c730253ab85c..583cbcf09446 100644
> --- a/drivers/video/fbdev/core/fb_defio.c
> +++ b/drivers/video/fbdev/core/fb_defio.c
> @@ -313,7 +313,7 @@ void fb_deferred_io_open(struct fb_info *info,
>  }
>  EXPORT_SYMBOL_GPL(fb_deferred_io_open);
>  
> -void fb_deferred_io_cleanup(struct fb_info *info)
> +void fb_deferred_io_release(struct fb_info *info)
>  {
>  	struct fb_deferred_io *fbdefio = info->fbdefio;
>  	struct page *page;
> @@ -327,6 +327,14 @@ void fb_deferred_io_cleanup(struct fb_info *info)
>  		page = fb_deferred_io_page(info, i);
>  		page->mapping = NULL;
>  	}
> +}
> +EXPORT_SYMBOL_GPL(fb_deferred_io_release);
> +
> +void fb_deferred_io_cleanup(struct fb_info *info)
> +{
> +	struct fb_deferred_io *fbdefio = info->fbdefio;
> +
> +	fb_deferred_io_release(info);
>  
>  	kvfree(info->pagerefs);
>  	mutex_destroy(&fbdefio->lock);
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 3a6c8458eb8d..78c4cb5ee7c9 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1454,6 +1454,8 @@ __releases(&info->lock)
>  	struct fb_info * const info = file->private_data;
>  
>  	lock_fb_info(info);
> +	if (info->fbdefio)
> +		fb_deferred_io_release(info);
>  	if (info->fbops->fb_release)
>  		info->fbops->fb_release(info,1);
>  	module_put(info->fbops->owner);
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 96b96323e9cb..73eb1f85ea8e 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -662,6 +662,7 @@ extern int  fb_deferred_io_init(struct fb_info *info);
>  extern void fb_deferred_io_open(struct fb_info *info,
>  				struct inode *inode,
>  				struct file *file);
> +extern void fb_deferred_io_release(struct fb_info *info);
>  extern void fb_deferred_io_cleanup(struct fb_info *info);
>  extern int fb_deferred_io_fsync(struct file *file, loff_t start,
>  				loff_t end, int datasync);
> -- 
> 2.35.3
>