linux-kernel - Re: [PATCH net] net/sched: cls_api: Initialize miss_cookie

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Date:   Thu, 20 Apr 2023 15:21:06 -0300
From:   Pedro Tammela <pctammela@...atatu.com>
To:     Ivan Vecera <ivecera@...hat.com>, netdev@...r.kernel.org
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Paul Blakey <paulb@...dia.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net/sched: cls_api: Initialize miss_cookie_node when
 action miss is not used

On 20/04/2023 14:59, Ivan Vecera wrote:
> Function tcf_exts_init_ex() sets exts->miss_cookie_node ptr only
> when use_action_miss is true so it assumes in other case that
> the field is set to NULL by the caller. If not then the field
> contains garbage and subsequent tcf_exts_destroy() call results
> in a crash.
> Initialize .miss_cookie_node pointer to NULL when use_action_miss
> parameter is false to avoid this potential scenario.
> 
> Fixes: 80cd22c35c90 ("net/sched: cls_api: Support hardware miss to tc action")
> Signed-off-by: Ivan Vecera <ivecera@...hat.com>
> ---
>   net/sched/cls_api.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 35785a36c80298..8bc5b9d6a2916e 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -3224,8 +3224,12 @@ int tcf_exts_init_ex(struct tcf_exts *exts, struct net *net, int action,
>   	exts->action = action;
>   	exts->police = police;
>   
> -	if (!use_action_miss)
> +	if (!use_action_miss) {
> +#ifdef CONFIG_NET_CLS_ACT
> +		exts->miss_cookie_node = NULL;
> +#endif
>   		return 0;
> +	}
>   
>   	err = tcf_exts_miss_cookie_base_alloc(exts, tp, handle);
>   	if (err)

The problem described here also happens in the case some error happens 
if the action array allocation fails and before the 'miss_cookie_node' 
assignment inside 'tcf_exts_miss_cookie_base_alloc()'.

Seems like a better way to solve this issue is to just:
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 35785a36c802..3c3629c9e7b6 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3211,6 +3211,7 @@ int tcf_exts_init_ex(struct tcf_exts *exts, struct 
net *net, int action,
  #ifdef CONFIG_NET_CLS_ACT
         exts->type = 0;
         exts->nr_actions = 0;
+       exts->miss_cookie_node = NULL;
         /* Note: we do not own yet a reference on net.
          * This reference might be taken later from tcf_exts_get_net().
          */