From patchwork Fri Jun 16 15:27:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bin Meng X-Patchwork-Id: 13282892 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 6F89DEB64DA for ; Fri, 16 Jun 2023 15:29:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qABNz-0006R4-3F; Fri, 16 Jun 2023 11:29:15 -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 1qABNw-0006J3-Kf for qemu-devel@nongnu.org; Fri, 16 Jun 2023 11:29:13 -0400 Received: from bg4.exmail.qq.com ([43.155.67.158]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qABNu-0000vu-Kk for qemu-devel@nongnu.org; Fri, 16 Jun 2023 11:29:12 -0400 X-QQ-mid: bizesmtp84t1686929281t57hu2x1 Received: from ubuntu.. ( [111.196.130.174]) by bizesmtp.qq.com (ESMTP) with id ; Fri, 16 Jun 2023 23:28:00 +0800 (CST) X-QQ-SSF: 01200000000000E0G000000A0000000 X-QQ-FEAT: +oIWmpEafD9b17Bsn3l+qM6TfpSiQMig/2jVKbBg+YupV8DneZMJaIk3iMQXU 0GkGy2BYh5vXgTmc4PtjryjdaCLPg4Hi426N57fYIQbG+iR61RgPsnZJD/elQdRHvMZNYRx XSqX1Gtw9WnbiC2vBPt0GO3bx15L6jf4pPMIdkkq4TDqBWwU+Ps9hXbkjF5xgJyw+hYX5e4 EXwKumk9dUAadYv4A2uEykFWCRfibvKBL8Q7KAuIAuiTW/DZNq6XnLxuzjSqRRTef3p2hON LyO+8Qg7kNXsXNJR/N+KtIrjBIIcfwtoWC1Wmmtt+v8QdpwThdAiyugTQdcMNLSporkeDH7 NW3k/PN/ZjfqEMZjDCC11bY7ouOu2bxBe9IdoP+dJV1wBFeB6LjOH/7z/lrWg== X-QQ-GoodBg: 0 X-BIZMAIL-ID: 4716907015537848369 From: Bin Meng To: qemu-devel@nongnu.org Cc: Zhangjin Wu , Jason Wang Subject: [PATCH v2 6/6] net: tap: Use qemu_close_range() to close fds Date: Fri, 16 Jun 2023 23:27:37 +0800 Message-Id: <20230616152737.23545-7-bmeng@tinylab.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230616152737.23545-1-bmeng@tinylab.org> References: <20230616152737.23545-1-bmeng@tinylab.org> MIME-Version: 1.0 X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:tinylab.org:qybglogicsvrgz:qybglogicsvrgz7a-0 Received-SPF: pass client-ip=43.155.67.158; 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 Signed-off-by: Zhangjin Wu Signed-off-by: Bin Meng Reviewed-by: Richard Henderson --- 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]);