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Subject: Re: [PATCH v4] mm/hugetlb: Fix unsigned overflow in
 __nr_hugepages_store_common()
To:     Jing Xiangfeng <jingxiangfeng@huawei.com>, mhocko@kernel.org
Cc:     akpm@linux-foundation.org, hughd@google.com, linux-mm@kvack.org,
        n-horiguchi@ah.jp.nec.com, aarcange@redhat.com,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org
References: <1550885529-125561-1-git-send-email-jingxiangfeng@huawei.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <388cbbf5-7086-1d04-4c49-049021504b9d@oracle.com>
Date:   Sun, 24 Feb 2019 16:45:15 -0800
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On 2/22/19 5:32 PM, Jing Xiangfeng wrote:
> User can change a node specific hugetlb count. i.e.
> /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
> the calculated value of count is a total number of huge pages. It could
> be overflow when a user entering a crazy high value. If so, the total
> number of huge pages could be a small value which is not user expect.
> We can simply fix it by setting count to ULONG_MAX, then it goes on. This
> may be more in line with user's intention of allocating as many huge pages
> as possible.
> 
> Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>

Thank you.

Acked-by: Mike Kravetz <mike.kravetz@oracle.com>

> ---
>  mm/hugetlb.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index afef616..6688894 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2423,7 +2423,14 @@ static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
>  		 * per node hstate attribute: adjust count to global,
>  		 * but restrict alloc/free to the specified node.
>  		 */
> +		unsigned long old_count = count;
>  		count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
> +		/*
> +		 * If user specified count causes overflow, set to
> +		 * largest possible value.
> +		 */
> +		if (count < old_count)
> +			count = ULONG_MAX;
>  		init_nodemask_of_node(nodes_allowed, nid);
>  	} else
>  		nodes_allowed = &node_states[N_MEMORY];
>