linux-kernel - Re: [RFC PATCH v2 2/4] mm/madvise: split out madvise input validity check

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Message-ID: <15ded8f6-bed7-4216-ad9c-3d51c84c7eb8@lucifer.local>
Date: Fri, 31 Jan 2025 16:01:55 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH v2 2/4] mm/madvise: split out madvise input validity
 check

On Thu, Jan 16, 2025 at 05:30:56PM -0800, SeongJae Park wrote:
> Split out the madvise parameters validation logic from do_madvise(), for
> easy reuse of the logic from a future change.
>
> Signed-off-by: SeongJae Park <sj@...nel.org>

Another decent cleanup, regardless of appllication, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/madvise.c | 32 ++++++++++++++++++++++----------
>  1 file changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index ae0964bc4d88..9cc31efe875a 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1592,6 +1592,27 @@ static void madvise_unlock(struct mm_struct *mm, int behavior)
>  		mmap_read_unlock(mm);
>  }
>
> +static bool is_valid_madvise(unsigned long start, size_t len_in, int behavior)
> +{
> +	size_t len;
> +
> +	if (!madvise_behavior_valid(behavior))
> +		return false;
> +
> +	if (!PAGE_ALIGNED(start))
> +		return false;
> +	len = PAGE_ALIGN(len_in);

Kind of a pity to duplicate this, but not exactly a big deal.

> +
> +	/* Check to see whether len was rounded up from small -ve to zero */
> +	if (len_in && !len)
> +		return false;
> +
> +	if (start + len < start)
> +		return false;
> +
> +	return true;
> +}
> +
>  /*
>   * The madvise(2) system call.
>   *
> @@ -1671,20 +1692,11 @@ int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int beh
>  	size_t len;
>  	struct blk_plug plug;
>
> -	if (!madvise_behavior_valid(behavior))
> +	if (!is_valid_madvise(start, len_in, behavior))
>  		return -EINVAL;
>
> -	if (!PAGE_ALIGNED(start))
> -		return -EINVAL;
>  	len = PAGE_ALIGN(len_in);
> -
> -	/* Check to see whether len was rounded up from small -ve to zero */
> -	if (len_in && !len)
> -		return -EINVAL;
> -
>  	end = start + len;
> -	if (end < start)
> -		return -EINVAL;
>
>  	if (end == start)
>  		return 0;
> --
> 2.39.5