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SubjectRe: [PATCH v2] rapidio: fix possible UAF when kfifo_alloc() fails
On Sat, 19 Nov 2022 12:03:35 +0800 Wang Weiyang <wangweiyang2@huawei.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.

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