From patchwork Mon Aug 24 08:31:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 265049 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7B18C433DF for ; Mon, 24 Aug 2020 09:34:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A7622075B for ; Mon, 24 Aug 2020 09:34:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598261681; bh=kH1Gs07rL+ujP0i+NK1hCa/O4lysoLbawWx5IuwWIp4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=SAM8dh9LtrEgCVsrOFIXJqcGiSaHuFlCveoZrpY9gMb+TbOahijIjYFl1EwtD4K0m CPlaqIhQtJ3hmNVj0JAf+/+RtF1KlnzntPfLqREfsOd2nDCqGlItl0gtmjB6DHs7By T0vldu8e0BacPtJxXfvXg+T3+QVgW6RESjgTKeFg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728182AbgHXJek (ORCPT ); Mon, 24 Aug 2020 05:34:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:51838 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729713AbgHXIt3 (ORCPT ); Mon, 24 Aug 2020 04:49:29 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 653D22072D; Mon, 24 Aug 2020 08:49:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598258968; bh=kH1Gs07rL+ujP0i+NK1hCa/O4lysoLbawWx5IuwWIp4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yfzEAme6G7dbISxQGZdxSlHv7rDZGfxlYqN30H2FiMy6P3ZhXIuwlsrORMaFCmnMY GoZ7B+6XDM1KCvJ7OQa9nGdKq+0kNurqPhCP8xm6CKwUw9xwFwVON/qjdtaHbbONIT nC+5DBJPJOSMc7hBwRmiDe3S3IbYe8SH2zJ6Bc84= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Marc Zyngier , Al Viro Subject: [PATCH 5.4 104/107] epoll: Keep a reference on files added to the check list Date: Mon, 24 Aug 2020 10:31:10 +0200 Message-Id: <20200824082410.243017384@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200824082405.020301642@linuxfoundation.org> References: <20200824082405.020301642@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Marc Zyngier commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682 upstream. When adding a new fd to an epoll, and that this new fd is an epoll fd itself, we recursively scan the fds attached to it to detect cycles, and add non-epool files to a "check list" that gets subsequently parsed. However, this check list isn't completely safe when deletions can happen concurrently. To sidestep the issue, make sure that a struct file placed on the check list sees its f_count increased, ensuring that a concurrent deletion won't result in the file disapearing from under our feet. Cc: stable@vger.kernel.org Signed-off-by: Marc Zyngier Signed-off-by: Al Viro Signed-off-by: Marc Zyngier Signed-off-by: Greg Kroah-Hartman --- fs/eventpoll.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1991,9 +1991,11 @@ static int ep_loop_check_proc(void *priv * not already there, and calling reverse_path_check() * during ep_insert(). */ - if (list_empty(&epi->ffd.file->f_tfile_llink)) + if (list_empty(&epi->ffd.file->f_tfile_llink)) { + get_file(epi->ffd.file); list_add(&epi->ffd.file->f_tfile_llink, &tfile_check_list); + } } } mutex_unlock(&ep->mtx); @@ -2037,6 +2039,7 @@ static void clear_tfile_check_list(void) file = list_first_entry(&tfile_check_list, struct file, f_tfile_llink); list_del_init(&file->f_tfile_llink); + fput(file); } INIT_LIST_HEAD(&tfile_check_list); } @@ -2196,9 +2199,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, in clear_tfile_check_list(); goto error_tgt_fput; } - } else + } else { + get_file(tf.file); list_add(&tf.file->f_tfile_llink, &tfile_check_list); + } mutex_lock_nested(&ep->mtx, 0); if (is_file_epoll(tf.file)) { tep = tf.file->private_data;