linux-kernel - Re: [RFC PATCH 8/9] orangefs: use set/clear_fs_page

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Date:   Mon, 27 Apr 2020 11:27:07 +0800
From:   Gao Xiang <hsiangkao@....com>
To:     Dave Chinner <david@...morbit.com>
Cc:     Guoqing Jiang <guoqing.jiang@...ud.ionos.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        hch@...radead.org, willy@...radead.org,
        Mike Marshall <hubcap@...ibond.com>,
        Martin Brandenburg <martin@...ibond.com>,
        devel@...ts.orangefs.org
Subject: Re: [RFC PATCH 8/9] orangefs: use set/clear_fs_page_private

On Mon, Apr 27, 2020 at 10:58:02AM +0800, Gao Xiang wrote:
> On Mon, Apr 27, 2020 at 08:24:55AM +1000, Dave Chinner wrote:
> > 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@...ibond.com>
> > > Cc: Martin Brandenburg <martin@...ibond.com>
> > > Cc: devel@...ts.orangefs.org
> > > Signed-off-by: Guoqing Jiang <guoqing.jiang@...ud.ionos.com>
> > > ---
> > >  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.
> 
> I'm not familar with orangefs. In my opinion, generally all temporary
> page->private access (r/w) should be properly protected by some locks,

... page->private pointers (there may be some other uses rather than
as references). sorry about that...

> most of time I think it could be at least page lock since .migratepage,
> .invalidatepage, .releasepage, .. (such paths) are already called with
> page locked (honestly I'm interested in this topic, please correct me
> if I'm wrong).
> 
> I agree that the suggested modification is more clear and easy to read.
> 
> Thanks,
> Gao Xiang
> 
>