Subject: Re: [PATCH net-next 2/6] net/sched: netem: check for invalid slot range

From: Jakub Kicinski <[email-masked]>
Date: Mon, 30 Mar 2026 17:32:46 -0700

On Sat, 28 Mar 2026 11:26:03 -0700 Stephen Hemminger wrote:
> Reject slot configuration where min_delay exceeds max_delay.
> The delay range computation in get_slot_next() underflows in
> this case, producing bogus results.
> 
> Fixes: 0a9fe5c375b5 ("netem: slotting with non-uniform distribution")
> 

spurious new line, but something either is a fix, gets a Fixes tag 
and goes to net, or it's not a fix and goes to net-next. No fixes 
in net-next please.

> Signed-off-by: Stephen Hemminger <[email-masked]>
> ---
>  net/sched/sch_netem.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> index 73d0e85eeadc..de22d754cb79 100644
> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -831,6 +831,17 @@ static int get_dist_table(struct disttable **tbl, const struct nlattr *attr,
>  	return 0;
>  }
>  
> +static int validate_slot(const struct nlattr *attr, struct netlink_ext_ack *extack)
> +{
> +	const struct tc_netem_slot *c = nla_data(attr);
> +
> +	if (c->min_delay > c->max_delay) {
> +		NL_SET_ERR_MSG(extack, "slot min delay greater than max delay");

This wants _ATTR ?

> +		return -EINVAL;
> +	}
> +	return 0;
> +}
> +
>  static void get_slot(struct netem_sched_data *q, const struct nlattr *attr)
>  {
>  	const struct tc_netem_slot *c = nla_data(attr);
> @@ -1045,6 +1056,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt, struct netlink_ex
>  			goto table_free;
>  	}
>  
> +	if (tb[TCA_NETEM_SLOT]) {
> +		ret = validate_slot(tb[TCA_NETEM_SLOT], extack);
> +		if (ret)
> +			goto table_free;
> +	}