linux-kernel - Re: [PATCH 3/6] aio: refactor read/write iocb setup

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Date:   Fri, 6 Apr 2018 09:10:11 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] aio: refactor read/write iocb setup

On Fri, Apr 06, 2018 at 04:21:46AM +0100, Al Viro wrote:
> On Wed, Mar 28, 2018 at 09:26:36AM +0200, Christoph Hellwig wrote:
> > +		struct inode *inode = file_inode(file);
> > +
> >  		req->ki_flags |= IOCB_WRITE;
> >  		file_start_write(file);
> > -		ret = aio_ret(req, call_write_iter(file, req, &iter));
> > +		ret = aio_rw_ret(req, call_write_iter(file, req, &iter));
> >  		/*
> > -		 * We release freeze protection in aio_complete().  Fool lockdep
> > -		 * by telling it the lock got released so that it doesn't
> > -		 * complain about held lock when we return to userspace.
> > +		 * We release freeze protection in aio_complete_rw().  Fool
> > +		 * lockdep by telling it the lock got released so that it
> > +		 * doesn't complain about held lock when we return to userspace.
> >  		 */
> > -		if (S_ISREG(file_inode(file)->i_mode))
> > -			__sb_writers_release(file_inode(file)->i_sb, SB_FREEZE_WRITE);
> > +		if (S_ISREG(inode->i_mode))
> 
> ... and that's another use-after-free, since we might've already done fput() of
> that sucker by that point.

Indeed.  Not in any way new in this patch, this is an existing issue
dating way back that needs to be fixed, which will be rather annoying
without taking an extra reference to the inode or at least sb.