Re: [PATCH] infiniband/core: Fix a use after free in cm_work_handler

[Leon Romanovsky <leon@kernel.org>]

On Wed, Mar 10, 2021 at 06:21:53PM -0800, Lv Yunlong wrote:
> In cm_work_handler, it calls destory_cm_id() to release
> the initial reference of cm_id_priv taken by iw_create_cm_id()
> and free the cm_id_priv. After destory_cm_id(), iwcm_deref_id
> (cm_id_priv) will be called and cause a use after free.
>
> Fixes: 59c68ac31e15a ("iw_cm: free cm_id resources on the last deref")
> Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> ---
>  drivers/infiniband/core/iwcm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/core/iwcm.c b/drivers/infiniband/core/iwcm.c
> index da8adadf4755..cb6b4ac45e21 100644
> --- a/drivers/infiniband/core/iwcm.c
> +++ b/drivers/infiniband/core/iwcm.c
> @@ -1035,8 +1035,10 @@ static void cm_work_handler(struct work_struct *_work)
>
>  		if (!test_bit(IWCM_F_DROP_EVENTS, &cm_id_priv->flags)) {
>  			ret = process_event(cm_id_priv, &levent);
> -			if (ret)
> +			if (ret) {
>  				destroy_cm_id(&cm_id_priv->id);
> +				return;

The destroy_cm_id() is called to free ->id and not cm_id_priv. This "return"
leaks cm_id_priv now and what "a use after free" do you see?

> +			}
>  		} else
>  			pr_debug("dropping event %d\n", levent.event);
>  		if (iwcm_deref_id(cm_id_priv))
> --
> 2.25.1
>
>