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

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Date:   Fri, 6 Apr 2018 04:21:46 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christoph Hellwig <hch@....de>
Cc:     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 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.

> +			__sb_writers_release(inode->i_sb, SB_FREEZE_WRITE);