linux-kernel - Re: [PATCH v2] rapidio: fix possible UAF when kfifo

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Message-Id: <20221121140410.dfe2816f743c62fe0c71639d@linux-foundation.org>
Date:   Mon, 21 Nov 2022 14:04:10 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wang Weiyang <wangweiyang2@...wei.com>
Cc:     <mporter@...nel.crashing.org>, <alex.bou9@...il.com>,
        <yangyingliang@...wei.com>, <jakobkoschel@...il.com>,
        <jhubbard@...dia.com>, <error27@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] rapidio: fix possible UAF when kfifo_alloc() fails

On Sat, 19 Nov 2022 12:03:35 +0800 Wang Weiyang <wangweiyang2@...wei.com> wrote:

> If kfifo_alloc() fails in mport_cdev_open(), goto err_fifo and just free
> priv. But priv is still in the chdev->file_list, then list traversal
> may cause UAF. This fixes the following smatch warning:
> 
> drivers/rapidio/devices/rio_mport_cdev.c:1930 mport_cdev_open() warn: '&priv->list' not removed from list
> 
> ...
>
> Changes in v2:
> - Avoid adding the new instance onto the list until the new instance
>   has been fully initialized.

But it still isn't fully initialized.

>  drivers/rapidio/devices/rio_mport_cdev.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index 3cc83997a1f8..86b28c4cd906 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -1904,10 +1904,6 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
>  
>  	priv->md = chdev;
>  
> -	mutex_lock(&chdev->file_mutex);
> -	list_add_tail(&priv->list, &chdev->file_list);
> -	mutex_unlock(&chdev->file_mutex);
> -
>  	INIT_LIST_HEAD(&priv->db_filters);
>  	INIT_LIST_HEAD(&priv->pw_filters);
>  	spin_lock_init(&priv->fifo_lock);
> @@ -1920,6 +1916,9 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
>  		ret = -ENOMEM;
>  		goto err_fifo;
>  	}
> +	mutex_lock(&chdev->file_mutex);
> +	list_add_tail(&priv->list, &chdev->file_list);
> +	mutex_unlock(&chdev->file_mutex);
>  
>  #ifdef CONFIG_RAPIDIO_DMA_ENGINE
>  	INIT_LIST_HEAD(&priv->async_list);

Here we're still setting up state at *priv.  I'm thinking the list
addition shouldn't occur until after the 

	filp->private_data = priv;

Or just prior to it.  I'm not sure what the atomicity rules are for
file.private versus mport_dev.file_list.