[PATCH] hugetlbfs: fix protential null pointer dereference

[Yufen Yu <yuyufen@huawei.com>]

After commit 58b6e5e8f1ad ("hugetlbfs: fix memory leak for resv_map"),
i_mapping->private_data will be NULL for mode that is not regular and link.
Then, it might cause NULL pointer derefernce in hugetlb_reserve_pages()
when do_mmap. We can avoid protential null pointer dereference by
judging whether it have been allocated.

Fixes: 58b6e5e8f1ad ("hugetlbfs: fix memory leak for resv_map")
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
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..15e4baf2aa7d 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 -EOPNOTSUPP;
 
 		chg = region_chg(resv_map, from, to);
 
-- 
2.16.2.dirty