[PATCH v2] hugetlbfs: Fix integer overflow check in hugetlbfs_file_mmap()

[Linke Li]

From: Linke Li <lilinke99@xxxxxxxxx>

```
	vma_len = (loff_t)(vma->vm_end - vma->vm_start);
	len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
	/* check for overflow */
	if (len < vma_len)
		return -EINVAL;
```

There is a signed integer overflow in the code, which is undefined
behavior according to the C stacnard. Although kernel disables some
optimizations by using the "-fno-strict-overflow" option, there is
still a risk.

Using macro "check_add_overflow" to do the overflow check can
effectively detect integer overflow and avoid any undefined behavior.

Signed-off-by: Linke Li <lilinke99@xxxxxxxxx>
---
 fs/hugetlbfs/inode.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 7b17ccfa039d..60f3010b0f71 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -155,9 +155,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 		return -EINVAL;
 
 	vma_len = (loff_t)(vma->vm_end - vma->vm_start);
-	len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
-	/* check for overflow */
-	if (len < vma_len)
+    if (check_add_overflow(vma_len, (loff_t)vma->vm_pgoff << PAGE_SHIFT, &len))
 		return -EINVAL;
 
 	inode_lock(inode);
-- 
2.25.1