diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c
index dbf5ec00b237..5868964e129c 100644
--- a/fs/ntfs3/index.c
+++ b/fs/ntfs3/index.c
@@ -1742,6 +1742,22 @@ static int indx_insert_into_root(struct ntfs_index *indx, struct ntfs_inode *ni,
 	hdr_used = le32_to_cpu(hdr->used);
 	hdr_total = le32_to_cpu(hdr->total);
 
+	/*
+	 * The destination INDEX_BUFFER has 'hdr_total' bytes of payload
+	 * available after the header, of which 'hdr_used' are already
+	 * consumed by the single terminal END entry installed by
+	 * indx_new(). A crafted image can present a resident root whose
+	 * non-last entries (summing to 'to_move') exceed what fits in
+	 * this buffer; copying them unchecked would overrun the
+	 * kmalloc(1u << indx->index_bits) allocation backing the new
+	 * buffer. Reject the copy in that case.
+	 */
+	if (to_move > hdr_total - hdr_used) {
+		err = -EINVAL;
+		ntfs_set_state(sbi, NTFS_DIRTY_ERROR);
+		goto out_put_n;
+	}
+
 	/* Copy root entries into new buffer. */
 	hdr_insert_head(hdr, re, to_move);