linux-kernel - [PATCH v3] mm/hugetlb: Fix unsigned overflow in __nr_hugepages_store

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Date:   Fri, 22 Feb 2019 22:01:28 +0800
From:   Jing Xiangfeng <jingxiangfeng@...wei.com>
To:     <mike.kravetz@...cle.com>, <mhocko@...nel.org>,
        <akpm@...ux-foundation.org>
CC:     <hughd@...gle.com>, <linux-mm@...ck.org>,
        <n-horiguchi@...jp.nec.com>, <aarcange@...hat.com>,
        <kirill.shutemov@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
        Jing Xiangfeng <jingxiangfeng@...wei.com>
Subject: [PATCH v3] mm/hugetlb: Fix unsigned overflow in  __nr_hugepages_store_common()

User can change a node specific hugetlb count. i.e.
/sys/devices/system/node/node1/hugepages/hugepages-2048kB
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@...wei.com>
---
 mm/hugetlb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index afef616..18fa7d7 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2423,7 +2423,10 @@ 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 (count < old_count)
+			count = ULONG_MAX;
 		init_nodemask_of_node(nodes_allowed, nid);
 	} else
 		nodes_allowed = &node_states[N_MEMORY];
-- 
2.7.4