ksmbd: handle smb2 query dir request for OutputBufferLength that is too small

We found the issue that ksmbd return STATUS_NO_MORE_FILES response
even though there are still dentries that needs to be read while
file read/write test using framtest utils.
windows client send smb2 query dir request included
OutputBufferLength(128) that is too small to contain even one entry.
This patch make ksmbd immediately returns OutputBufferLength of response
as zero to client.
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smb2pdu.c

@@ -3938,6 +3938,12 @@ int smb2_query_dir(struct ksmbd_work *work)
 	set_ctx_actor(&dir_fp->readdir_data.ctx, __query_dir);
 
 	rc = iterate_dir(dir_fp->filp, &dir_fp->readdir_data.ctx);
+	/*
+	 * req->OutputBufferLength is too small to contain even one entry.
+	 * In this case, it immediately returns OutputBufferLength 0 to client.
+	 */
+	if (!d_info.out_buf_len && !d_info.num_entry)
+		goto no_buf_len;
 	if (rc == 0)
 		restart_ctx(&dir_fp->readdir_data.ctx);
 	if (rc == -ENOSPC)
@@ -3964,10 +3970,12 @@ int smb2_query_dir(struct ksmbd_work *work)
 		rsp->Buffer[0] = 0;
 		inc_rfc1001_len(work->response_buf, 9);
 	} else {
+no_buf_len:
 		((struct file_directory_info *)
 		((char *)rsp->Buffer + d_info.last_entry_offset))
 		->NextEntryOffset = 0;
-		d_info.data_count -= d_info.last_entry_off_align;
+		if (d_info.data_count >= d_info.last_entry_off_align)
+			d_info.data_count -= d_info.last_entry_off_align;
 
 		rsp->StructureSize = cpu_to_le16(9);
 		rsp->OutputBufferOffset = cpu_to_le16(72);