[PATCH] mm/hugetlb: Fix unsigned overflow in __nr_hugepages_store_common()

[Jingxiangfeng]

From: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx>

We can use the following command to dynamically allocate huge pages:
	echo NR_HUGEPAGES > /proc/sys/vm/nr_hugepages
The count in  __nr_hugepages_store_common() is parsed from /proc/sys/vm/nr_hugepages,
The maximum number of count is ULONG_MAX,
the operation 'count += h->nr_huge_pages - h->nr_huge_pages_node[nid]' overflow and count will be a wrong number.
So check the overflow to fix this problem.

Signed-off-by: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx>
---
 mm/hugetlb.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index afef616..55173c3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2423,7 +2423,12 @@ 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) {
+			err = -EINVAL;
+			goto out;
+		}
 		init_nodemask_of_node(nodes_allowed, nid);
 	} else
 		nodes_allowed = &node_states[N_MEMORY];
-- 
2.7.4