[PATCH v2] hugetlbfs: fix protential null pointer dereference

[Yufen Yu <yuyufen@huawei.com>]

This patch can avoid protential null pointer dereference for resv_map.

As Mike Kravetz say:
    Even if we can not hit this condition today, I still believe it
    would be a good idea to make this type of change.  It would
    prevent a possible NULL dereference in case the structure of code
    changes in the future.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
---
 mm/hugetlb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 97b1e0290c66..fe74f94e5327 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4465,6 +4465,8 @@ int hugetlb_reserve_pages(struct inode *inode,
 	 */
 	if (!vma || vma->vm_flags & VM_MAYSHARE) {
 		resv_map = inode_resv_map(inode);
+		if (!resv_map)
+			return -EACCES;
 
 		chg = region_chg(resv_map, from, to);
 
-- 
2.16.2.dirty