netdev - Re: [PATCH iproute2-next] tc: mqprio: reject queues count/offset pair count higher than num

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Date:   Mon, 18 May 2020 08:08:10 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     dsahern@...il.com, netdev@...r.kernel.org, kiran.patil@...el.com
Subject: Re: [PATCH iproute2-next] tc: mqprio: reject queues count/offset
 pair count higher than num_tc

On Wed, 13 May 2020 21:47:17 +0200
Maciej Fijalkowski <maciej.fijalkowski@...el.com> wrote:

> Provide a sanity check that will make sure whether queues count/offset
> pair count will not exceed the actual number of TCs being created.
> 
> Example command that is invalid because there are 4 count/offset pairs
> whereas num_tc is only 2.
> 
>  # tc qdisc add dev enp96s0f0 root mqprio num_tc 2 map 0 0 0 0 1 1 1 1
> queues 4@0 4@4 4@8 4@12 hw 1 mode channel
> 
> Store the parsed count/offset pair count onto a dedicated variable that
> will be compared against opt.num_tc after all of the command line
> arguments were parsed. Bail out if this count is higher than opt.num_tc
> and let user know about it.
> 
> Drivers were swallowing such commands as they were iterating over
> count/offset pairs where num_tc was used as a delimiter, so this is not
> a big deal, but better catch such misconfiguration at the command line
> argument parsing level.
> 
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>  tc/q_mqprio.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tc/q_mqprio.c b/tc/q_mqprio.c
> index 0eb41308..f26ba8d7 100644
> --- a/tc/q_mqprio.c
> +++ b/tc/q_mqprio.c
> @@ -48,6 +48,7 @@ static int mqprio_parse_opt(struct qdisc_util *qu, int argc,
>  	__u64 max_rate64[TC_QOPT_MAX_QUEUE] = {0};
>  	__u16 shaper = TC_MQPRIO_SHAPER_DCB;
>  	__u16 mode = TC_MQPRIO_MODE_DCB;
> +	int cnt_off_pairs = 0;

Since opt.num_tc is u8, shouldn't this be u8 as well?
Note: maximum number of queue is TC_QOPT_MAX_QUEUE (16).