Re: [PATCH v4 net-next 2/9] net/sched: mqprio: simplify handling of nlattr portion of TCA_OPTIONS

[Jamal Hadi Salim]

On Mon, Apr 3, 2023 at 6:35 AM Vladimir Oltean <vladimir.oltean@xxxxxxx> wrote:
>
> In commit 4e8b86c06269 ("mqprio: Introduce new hardware offload mode and
> shaper in mqprio"), the TCA_OPTIONS format of mqprio was extended to
> contain a fixed portion (of size NLA_ALIGN(sizeof struct tc_mqprio_qopt))
> and a variable portion of other nlattrs (in the TCA_MQPRIO_* type space)
> following immediately afterwards.
>
> In commit feb2cf3dcfb9 ("net/sched: mqprio: refactor nlattr parsing to a
> separate function"), we've moved the nlattr handling to a smaller
> function, but yet, a small parse_attr() still remains, and the larger
> mqprio_parse_nlattr() still does not have access to the beginning, and
> the length, of the TCA_OPTIONS region containing these other nlattrs.
>
> In a future change, the mqprio qdisc will need to iterate through this
> nlattr region to discover other attributes, so eliminate parse_attr()
> and add 2 variables in mqprio_parse_nlattr() which hold the beginning
> and the length of the nlattr range.
>
> We avoid the need to memset when nlattr_opt_len has insufficient length
> by pre-initializing the table "tb".
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> Reviewed-by: Ferenc Fejes <fejes@xxxxxxxxxxx>
> Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>

Acked-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>

cheers,
jamal

> ---
> v1->v4: none
>
>  net/sched/sch_mqprio.c | 32 +++++++++++++-------------------
>  1 file changed, 13 insertions(+), 19 deletions(-)
>
> diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
> index 48ed87b91086..94093971da5e 100644
> --- a/net/sched/sch_mqprio.c
> +++ b/net/sched/sch_mqprio.c
> @@ -146,32 +146,26 @@ static const struct nla_policy mqprio_policy[TCA_MQPRIO_MAX + 1] = {
>         [TCA_MQPRIO_MAX_RATE64] = { .type = NLA_NESTED },
>  };
>
> -static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
> -                     const struct nla_policy *policy, int len)
> -{
> -       int nested_len = nla_len(nla) - NLA_ALIGN(len);
> -
> -       if (nested_len >= nla_attr_size(0))
> -               return nla_parse_deprecated(tb, maxtype,
> -                                           nla_data(nla) + NLA_ALIGN(len),
> -                                           nested_len, policy, NULL);
> -
> -       memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
> -       return 0;
> -}
> -
> +/* Parse the other netlink attributes that represent the payload of
> + * TCA_OPTIONS, which are appended right after struct tc_mqprio_qopt.
> + */
>  static int mqprio_parse_nlattr(struct Qdisc *sch, struct tc_mqprio_qopt *qopt,
>                                struct nlattr *opt)
>  {
> +       struct nlattr *nlattr_opt = nla_data(opt) + NLA_ALIGN(sizeof(*qopt));
> +       int nlattr_opt_len = nla_len(opt) - NLA_ALIGN(sizeof(*qopt));
>         struct mqprio_sched *priv = qdisc_priv(sch);
> -       struct nlattr *tb[TCA_MQPRIO_MAX + 1];
> +       struct nlattr *tb[TCA_MQPRIO_MAX + 1] = {};
>         struct nlattr *attr;
>         int i, rem, err;
>
> -       err = parse_attr(tb, TCA_MQPRIO_MAX, opt, mqprio_policy,
> -                        sizeof(*qopt));
> -       if (err < 0)
> -               return err;
> +       if (nlattr_opt_len >= nla_attr_size(0)) {
> +               err = nla_parse_deprecated(tb, TCA_MQPRIO_MAX, nlattr_opt,
> +                                          nlattr_opt_len, mqprio_policy,
> +                                          NULL);
> +               if (err < 0)
> +                       return err;
> +       }
>
>         if (!qopt->hw)
>                 return -EINVAL;
> --
> 2.34.1
>