Re: [RFC PATCH 8/9] orangefs: use set/clear_fs_page_private

[Dave Chinner]

On Sun, Apr 26, 2020 at 11:49:24PM +0200, Guoqing Jiang wrote:
> Since the new pair function is introduced, we can call them to clean the
> code in orangefs.
> 
> Cc: Mike Marshall <hubcap@xxxxxxxxxxxx>
> Cc: Martin Brandenburg <martin@xxxxxxxxxxxx>
> Cc: devel@xxxxxxxxxxxxxxxxxx
> Signed-off-by: Guoqing Jiang <guoqing.jiang@xxxxxxxxxxxxxxx>
> ---
>  fs/orangefs/inode.c | 24 ++++++------------------
>  1 file changed, 6 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/orangefs/inode.c b/fs/orangefs/inode.c
> index 12ae630fbed7..893099d36e20 100644
> --- a/fs/orangefs/inode.c
> +++ b/fs/orangefs/inode.c
> @@ -64,9 +64,7 @@ static int orangefs_writepage_locked(struct page *page,
>  	}
>  	if (wr) {
>  		kfree(wr);
> -		set_page_private(page, 0);
> -		ClearPagePrivate(page);
> -		put_page(page);
> +		clear_fs_page_private(page);

THis is a pre-existing potential use-after-free vector. The wr
pointer held in the page->private needs to be cleared from the page
before it is freed.

>  	}
>  	return ret;
>  }
> @@ -409,9 +407,7 @@ static int orangefs_write_begin(struct file *file,
>  	wr->len = len;
>  	wr->uid = current_fsuid();
>  	wr->gid = current_fsgid();
> -	SetPagePrivate(page);
> -	set_page_private(page, (unsigned long)wr);
> -	get_page(page);
> +	set_fs_page_private(page, wr);
>  okay:
>  	return 0;
>  }
> @@ -460,17 +456,13 @@ static void orangefs_invalidatepage(struct page *page,
>  
>  	if (offset == 0 && length == PAGE_SIZE) {
>  		kfree((struct orangefs_write_range *)page_private(page));
> -		set_page_private(page, 0);
> -		ClearPagePrivate(page);
> -		put_page(page);
> +		clear_fs_page_private(page);

Ditto:
		wr = clear_fs_page_private(page);
		kfree(wr);

>  		return;
>  	/* write range entirely within invalidate range (or equal) */
>  	} else if (page_offset(page) + offset <= wr->pos &&
>  	    wr->pos + wr->len <= page_offset(page) + offset + length) {
>  		kfree((struct orangefs_write_range *)page_private(page));
> -		set_page_private(page, 0);
> -		ClearPagePrivate(page);
> -		put_page(page);
> +		clear_fs_page_private(page);

And again.

>  		/* XXX is this right? only caller in fs */
>  		cancel_dirty_page(page);
>  		return;
> @@ -537,9 +529,7 @@ static void orangefs_freepage(struct page *page)
>  {
>  	if (PagePrivate(page)) {
>  		kfree((struct orangefs_write_range *)page_private(page));
> -		set_page_private(page, 0);
> -		ClearPagePrivate(page);
> -		put_page(page);
> +		clear_fs_page_private(page);

And again.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx