Re: [PATCH] rapidio: mport_cdev: fix sequential UAF in dma_req_free()

[James Kim]

Hi,

Just a gentle reminder about this patch.

It might have been missed during the previous merge window.

Thanks,
James

On Mon, Apr 6, 2026 at 10:50 AM James Kim <james010kim@xxxxxxxxx> wrote:
>
> dma_req_free() drops the mapping reference under buf_mutex and then
> dereferences req->map again to unlock the mutex.
>
> If kref_put() drops the last reference, mport_release_mapping() frees
> the mapping, and the subsequent mutex_unlock() dereferences a freed
> object. This is a sequential (non-racy) use-after-free.
>
> Fix this by caching map and md before kref_put() and using the cached
> md for mutex unlocking.
>
> Fixes: 4b0986a36 ("rapidio: add mport character device support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: James Kim <james010kim@xxxxxxxxx>
> ---
>  drivers/rapidio/devices/rio_mport_cdev.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> Resending this patch as it might have been missed due to the merge window.
>
> No changes since the previous submission.
>
> diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
> index 7df466e22282..5fb6ec439028 100644
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -582,9 +582,14 @@ static void dma_req_free(struct kref *ref)
>         }
>
>         if (req->map) {
> -               mutex_lock(&req->map->md->buf_mutex);
> -               kref_put(&req->map->ref, mport_release_mapping);
> -               mutex_unlock(&req->map->md->buf_mutex);
> +               struct rio_mport_mapping *map = req->map;
> +               struct mport_dev *md = map->md;
> +
> +               mutex_lock(&md->buf_mutex);
> +               kref_put(&map->ref, mport_release_mapping);
> +               mutex_unlock(&md->buf_mutex);
> +
> +               req->map = NULL;
>         }
>
>         kref_put(&priv->dma_ref, mport_release_dma);
> --
> 2.25.1
>