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From: Dan Carpenter <dan.carpenter@oracle.com>
To: George Acosta <acostag.ubuntu@gmail.com>
Cc: Matt Porter <mporter@kernel.crashing.org>,
	Alexandre Bounine <alex.bou9@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	John Hubbard <jhubbard@nvidia.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rapidio: fix get device imbalance on error
Date: Fri, 21 Aug 2020 11:14:49 +0300
Message-ID: <20200821081449.GI5493@kadam> (raw)
In-Reply-To: <20200821034458.22472-1-acostag.ubuntu@gmail.com>

On Thu, Aug 20, 2020 at 10:44:57PM -0500, George Acosta wrote:
> Fix the imbalance in mport_cdev_open.
> Call put_device in error path to balance the
> refcount that increased by the get_device.
> 
> Fixes: e8de370188d0 ("rapidio: add mport char device driver")
> Signed-off-by: George Acosta <acostag.ubuntu@gmail.com>
> ---
>  drivers/rapidio/devices/rio_mport_cdev.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index c07ceec3c6d4..3b68e00eb40f 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -1908,6 +1908,7 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
>  			  sizeof(struct rio_event) * MPORT_EVENT_DEPTH,
>  			  GFP_KERNEL);
>  	if (ret < 0) {
> +		put_device(&chdev->dev);
>  		dev_err(&chdev->dev, DRV_NAME ": kfifo_alloc failed\n");
>  		ret = -ENOMEM;
>  		goto err_fifo;
> -- 

If we ever hit this error path then the:

	list_add_tail(&priv->list, &chdev->file_list);

needs to be removed from the list as well or it lead to a use after
free.  Probably just move the list_add_tail() after the kfifo_alloc()
has succeeded. We need to remove it from the list in mport_cdev_release()
as well...

The error handling in this function is kind of rubbish.
1) Get rid of the out label and return directly (more readable).
1b) Use "return 0;" instead of "retur ret;" for the success path.
2) Name the labels after what they do not where they "come from".  In
other words do.

err_priv:
	kfree(priv);

3) Create a label to call put_device:

err_device:
	put_device(&chdev->dev);

Change all the error paths to use the goto instead of calling
put_device() before the goto.

regards,
dan carpenter

      reply index

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21  3:44 George Acosta
2020-08-21  8:14 ` Dan Carpenter [this message]

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