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

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Date:   Thu, 17 Nov 2022 12:45:17 -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] rapidio: fix possible UAF when kfifo_alloc() fails

On Thu, 17 Nov 2022 10:18:02 +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
> 
> Fixes: e8de370188d0 ("rapidio: add mport char device driver")
> Signed-off-by: Wang Weiyang <wangweiyang2@...wei.com>
> ---
>  drivers/rapidio/devices/rio_mport_cdev.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index 3cc83997a1f8..c66b2c552b38 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -1930,6 +1930,9 @@ static int mport_cdev_open(struct inode *inode, struct file *filp)
>  	filp->private_data = priv;
>  	goto out;
>  err_fifo:
> +	mutex_lock(&chdev->file_mutex);
> +	list_del(&priv->list);
> +	mutex_unlock(&chdev->file_mutex);
>  	kfree(priv);
>  out:
>  	return ret;

Surely it would be better to avoid adding the new instance onto the
list until the new instance has been fully initialized?