Re: [Patch net] net_sched: fix backward compatibility for TCA_ACT_KIND

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Mon, Oct 07, 2019 at 01:26:29PM -0700, Cong Wang wrote:
> For TCA_ACT_KIND, we have to keep the backward compatibility too,
> and rely on nla_strlcpy() to check and terminate the string with
> a NUL.
> 
> Note for TC actions, nla_strcmp() is already used to compare kind
> strings, so we don't need to fix other places.
> 
> Fixes: 199ce850ce11 ("net_sched: add policy validation for action attributes")
> Reported-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Cc: Jiri Pirko <jiri@resnulli.us>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  net/sched/act_api.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index da99667589f8..4684f2f24b17 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -832,8 +832,7 @@ static struct tc_cookie *nla_memdup_cookie(struct nlattr **tb)
>  }
>  
>  static const struct nla_policy tcf_action_policy[TCA_ACT_MAX + 1] = {
> -	[TCA_ACT_KIND]		= { .type = NLA_NUL_STRING,
> -				    .len = IFNAMSIZ - 1 },
> +	[TCA_ACT_KIND]		= { .type = NLA_STRING },
>  	[TCA_ACT_INDEX]		= { .type = NLA_U32 },
>  	[TCA_ACT_COOKIE]	= { .type = NLA_BINARY,
>  				    .len = TC_COOKIE_MAX_SIZE },
> @@ -865,8 +864,10 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
>  			NL_SET_ERR_MSG(extack, "TC action kind must be specified");
>  			goto err_out;
>  		}
> -		nla_strlcpy(act_name, kind, IFNAMSIZ);
> -
> +		if (nla_strlcpy(act_name, kind, IFNAMSIZ) >= IFNAMSIZ) {
> +			NL_SET_ERR_MSG(extack, "TC action name too long");
> +			goto err_out;
> +		}
>  		if (tb[TCA_ACT_COOKIE]) {
>  			cookie = nla_memdup_cookie(tb);
>  			if (!cookie) {
> -- 
> 2.21.0
>