linux-hardening - Re: [PATCH -next, v2] sched: Use struct_size() helper in task_numa

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Date:   Mon, 10 Jan 2022 23:46:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Xiu Jianfeng <xiujianfeng@...wei.com>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, gustavoars@...nel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH -next, v2] sched: Use struct_size() helper in
 task_numa_group()

On Mon, Jan 10, 2022 at 09:23:54AM +0800, Xiu Jianfeng wrote:
> Make use of struct_size() helper instead of an open-coded calculation.
> There is no functional change in this patch.
> 
> Link: https://github.com/KSPP/linux/issues/160
> Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
> ---
>  kernel/sched/fair.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 095b0aa378df..af933a7f9e5d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2437,9 +2437,8 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
>  	int i;
>  
>  	if (unlikely(!deref_curr_numa_group(p))) {
> -		unsigned int size = sizeof(struct numa_group) +
> -				    NR_NUMA_HINT_FAULT_STATS *
> -				    nr_node_ids * sizeof(unsigned long);
> +		unsigned int size = struct_size(grp, faults,
> +						NR_NUMA_HINT_FAULT_STATS * nr_node_ids);

Again, why?! The old code was perfectly readable, this, not so much.