From patchwork Sat Jun 17 05:36:21 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bin Meng X-Patchwork-Id: 13283445 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2E93CEB64D9 for ; Sat, 17 Jun 2023 05:37:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qAOcL-0003N0-0j; Sat, 17 Jun 2023 01:36:57 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qAOcJ-0003Mo-Je for qemu-devel@nongnu.org; Sat, 17 Jun 2023 01:36:55 -0400 Received: from bg4.exmail.qq.com ([43.154.221.58]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qAOcH-0006Ws-Jd for qemu-devel@nongnu.org; Sat, 17 Jun 2023 01:36:55 -0400 X-QQ-mid: bizesmtp73t1686980203tqp8xinx Received: from ubuntu.. ( [111.196.130.174]) by bizesmtp.qq.com (ESMTP) with id ; Sat, 17 Jun 2023 13:36:42 +0800 (CST) X-QQ-SSF: 01200000000000E0G000000A0000000 X-QQ-FEAT: Sb649gZU4sJPb/EvvUKTDf299KFDY5T2M2T8X4w9Gbd939gBOH7HMb0xADMtI npLIOoXy/eHjV4ugOnUqW5iSVQ0NaGDxlad9ZAAO24QEuPzT4MRdclYgVZSLxWyOBHDiJ2t 571F62mT07cHqLzprIypLCjMe4L8sB8TyP0HXZykBRuQuIY/N1JNbD/r/5s1K1bAlNby4By zoplx4Gy/n02dp/GOsfH5/OIH7Us7RHo9BquJLjVROcbGULI4HgZNGEJUcdvRNhC8kVFHQx lRO+3U5EsigqbBqLKekcYXMB1K0IBgRVXWXA1lLKd7yfBoBuHsqHr6NBkzGYAH5sagCc+io aXyKDDEKGuAsy1zS1L9bLlFWJjCNXW8EGuXDSAP6IwgFekglkRaAsOspt7LXRPn6c/Exm3f X-QQ-GoodBg: 0 X-BIZMAIL-ID: 2473288236721930917 From: Bin Meng To: qemu-devel@nongnu.org Cc: Zhangjin Wu , Jason Wang Subject: [PATCH v3 6/6] net: tap: Use qemu_close_range() to close fds Date: Sat, 17 Jun 2023 13:36:21 +0800 Message-Id: <20230617053621.50359-7-bmeng@tinylab.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230617053621.50359-1-bmeng@tinylab.org> References: <20230617053621.50359-1-bmeng@tinylab.org> MIME-Version: 1.0 X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:tinylab.org:qybglogicsvrgz:qybglogicsvrgz7a-0 Received-SPF: pass client-ip=43.154.221.58; envelope-from=bmeng@tinylab.org; helo=bg4.exmail.qq.com X-Spam_score_int: -17 X-Spam_score: -1.8 X-Spam_bar: - X-Spam_report: (-1.8 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, RCVD_IN_SBL=0.141, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Zhangjin Wu Current codes using a brute-force traversal of all file descriptors do not scale on a system where the maximum number of file descriptors is set to a very large value (e.g.: in a Docker container of Manjaro distribution it is set to 1073741816). QEMU just looks frozen during start-up. The close-on-exec flag (O_CLOEXEC) was introduced since Linux kernel 2.6.23, FreeBSD 8.3, OpenBSD 5.0, Solaris 11. While it's true QEMU doesn't need to manually close the fds for child process as the proper O_CLOEXEC flag should have been set properly on files with its own codes, QEMU uses a huge number of 3rd party libraries and we don't trust them to reliably be using O_CLOEXEC on everything they open. Modern Linux and BSDs have the close_range() call we can use to do the job, and on Linux we have one more way to walk through /proc/self/fd to complete the task efficiently, which is what qemu_close_range() does. Reported-by: Zhangjin Wu Co-developed-by: Bin Meng Signed-off-by: Zhangjin Wu Signed-off-by: Bin Meng --- (no changes since v2) Changes in v2: - Change to use qemu_close_range() to close fds for child process efficiently - v1 link: https://lore.kernel.org/qemu-devel/20230406112041.798585-1-bmeng@tinylab.org/ net/tap.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/net/tap.c b/net/tap.c index 1bf085d422..d482fabdff 100644 --- a/net/tap.c +++ b/net/tap.c @@ -446,13 +446,13 @@ static void launch_script(const char *setup_script, const char *ifname, return; } if (pid == 0) { - int open_max = sysconf(_SC_OPEN_MAX), i; + unsigned int last_fd = sysconf(_SC_OPEN_MAX) - 1; + + /* skip stdin, stdout and stderr */ + qemu_close_range(3, fd - 1); + /* skip the currently used fd */ + qemu_close_range(fd + 1, last_fd); - for (i = 3; i < open_max; i++) { - if (i != fd) { - close(i); - } - } parg = args; *parg++ = (char *)setup_script; *parg++ = (char *)ifname; @@ -536,16 +536,15 @@ static int net_bridge_run_helper(const char *helper, const char *bridge, return -1; } if (pid == 0) { - int open_max = sysconf(_SC_OPEN_MAX), i; + unsigned int last_fd = sysconf(_SC_OPEN_MAX) - 1, fd = sv[1]; char *fd_buf = NULL; char *br_buf = NULL; char *helper_cmd = NULL; - for (i = 3; i < open_max; i++) { - if (i != sv[1]) { - close(i); - } - } + /* skip stdin, stdout and stderr */ + qemu_close_range(3, fd - 1); + /* skip the currently used fd */ + qemu_close_range(fd + 1, last_fd); fd_buf = g_strdup_printf("%s%d", "--fd=", sv[1]);