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From:   SeongJae Park <sj@kernel.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     SeongJae Park <sj@kernel.org>,
        syzbot <syzbot+841a46899768ec7bec67@syzkaller.appspotmail.com>,
        akpm@linux-foundation.org, damon@lists.linux.dev,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [damon?] divide error in damon_set_attrs
Date:   Fri, 26 May 2023 18:46:35 -0700
Message-Id: <20230527014635.7380-1-sj@kernel.org>
In-Reply-To: <c18dc1e9-1805-f366-9d16-30e9628ac14e@huawei.com>
Precedence: bulk

Hi Kefeng,

On Sat, 27 May 2023 09:15:01 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:

[...]
> > 
> > Nice and effective fix!  Nevertheless, I think aggregation interval smaller
> > than sample interval is just a wrong input.  How about adding the check in
> > damon_set_attrs()'s already existing attributes validation, like below?
> 
> Yes, move the check into damon_set_attrs() is better

Thank you for this kind comment!

> , and it seems that
> we could move all the check into it, and drop the old_attrs check in
> damon_update_monitoring_results(), what's you option?
> 
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index d9ef62047bf5..1647f7f1f708 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -523,12 +523,6 @@ static void damon_update_monitoring_results(struct 
> damon_ctx *ctx,
>          struct damon_target *t;
>          struct damon_region *r;
> 
> -       /* if any interval is zero, simply forgive conversion */
> -       if (!old_attrs->sample_interval || !old_attrs->aggr_interval ||
> -                       !new_attrs->sample_interval ||
> -                       !new_attrs->aggr_interval)
> -               return;
> -
>          damon_for_each_target(t, ctx)
>                  damon_for_each_region(r, t)
>                          damon_update_monitoring_result(
> @@ -551,6 +545,10 @@ int damon_set_attrs(struct damon_ctx *ctx, struct 
> damon_attrs *attrs)
>                  return -EINVAL;
>          if (attrs->min_nr_regions > attrs->max_nr_regions)
>                  return -EINVAL;
> +       if (attrs->sample_interval > attrs->aggr_interval)
> +               return -EINVAL;
> +       if (!attrs->sample_interval || !attrs->aggr_interval)
> +               return -EINVAL;

In my humble opinion, the validation for monitoring results and for general
monitoring could be different.  For example, zero aggreation/sampling intervals
might make sense for fixed granularity working set size monitoring.  Hence, I'd
prefer keeping those checks in the damon_update_monitoring_results().


Thanks,
SJ

[...]