From mboxrd@z Thu Jan 1 00:00:00 1970 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=unavailable 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 3F26AC433E1 for ; Mon, 24 Aug 2020 09:30:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 105EC206B5 for ; Mon, 24 Aug 2020 09:30:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598261453; bh=/MhY6KOjYV5UQvfUwKDgkfVxzvA4mJRDHMCk6YPmWPk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=pjZqTpi48AjjNmCMtbQHZw5blNFDlv/lF7xh5zEaqfn+biTVGYRMGsQGxIWHH97I4 /VUuX/c7Z1kvRDvuKzz2gcN83xcNTCNHvG8hdFyodrfpo/CIbHCmrbHSfX0asCIKaN 6FhTzmaodct9U7WpglG6VdGdaAnZv/9Ic2J8LDw8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729225AbgHXIug (ORCPT ); Mon, 24 Aug 2020 04:50:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:54370 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729848AbgHXIuf (ORCPT ); Mon, 24 Aug 2020 04:50:35 -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 2A808204FD; Mon, 24 Aug 2020 08:50:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598259034; bh=/MhY6KOjYV5UQvfUwKDgkfVxzvA4mJRDHMCk6YPmWPk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MRJ6dWezHAJGibmMMlJSpoesqwBiyaCIkuc6ZzLizY8Xk0Rk7MWGQ1r+nPJHJeLOq 2k4ugAFMZQ5N/+Z5Tuem5ghee5Ip/zBfLxaoN84fW7eejvsZX2i/9RTzuqRtYqvb6T qmhIGXfL8Qr5F7IBFs/LYToFGwrEZs9qk2VEgGjY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Marc Zyngier , Al Viro Subject: [PATCH 4.4 29/33] epoll: Keep a reference on files added to the check list Date: Mon, 24 Aug 2020 10:31:25 +0200 Message-Id: <20200824082348.000514221@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200824082346.498653578@linuxfoundation.org> References: <20200824082346.498653578@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 @@ -1719,9 +1719,11 @@ 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); @@ -1765,6 +1767,7 @@ 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); } @@ -1906,9 +1909,11 @@ 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;