fs/ntfs3: Prevent integer overflow in hdr_first_de()

The "de_off" and "used" variables come from the disk so they both need to
check.  The problem is that on 32bit systems if they're both greater than
UINT_MAX - 16 then the check does work as intended because of an integer
overflow.

Fixes: 60ce8df ("fs/ntfs3: Fix wrong if in hdr_first_de")
Signed-off-by: Dan Carpenter <[email protected]>
Signed-off-by: Konstantin Komarov <[email protected]>

Author: Dan Carpenter

fs/ntfs3/ntfs.h

@@ -717,7 +717,7 @@ static inline struct NTFS_DE *hdr_first_de(const struct INDEX_HDR *hdr)
 	struct NTFS_DE *e;
 	u16 esize;
 
-	if (de_off >= used || de_off + sizeof(struct NTFS_DE) > used )
+	if (de_off >= used || size_add(de_off, sizeof(struct NTFS_DE)) > used)
 		return NULL;
 
 	e = Add2Ptr(hdr, de_off);