fs/ntfs3: Fix wrong if in hdr_first_de

We need to check used bytes instead of total.

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: aalexandrovich

fs/ntfs3/ntfs.h

@@ -714,12 +714,13 @@ static inline struct NTFS_DE *hdr_first_de(const struct INDEX_HDR *hdr)
 {
 	u32 de_off = le32_to_cpu(hdr->de_off);
 	u32 used = le32_to_cpu(hdr->used);
-	struct NTFS_DE *e = Add2Ptr(hdr, de_off);
+	struct NTFS_DE *e;
 	u16 esize;
 
-	if (de_off >= used || de_off >= le32_to_cpu(hdr->total))
+	if (de_off >= used || de_off + sizeof(struct NTFS_DE) > used )
 		return NULL;
 
+	e = Add2Ptr(hdr, de_off);
 	esize = le16_to_cpu(e->size);
 	if (esize < sizeof(struct NTFS_DE) || de_off + esize > used)
 		return NULL;