From patchwork Fri May 3 17:08:21 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andre Przywara X-Patchwork-Id: 10929049 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E10B91390 for ; Fri, 3 May 2019 17:08:34 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D3EE5205AD for ; Fri, 3 May 2019 17:08:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C83DB2859F; Fri, 3 May 2019 17:08:34 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 62EA3205AD for ; Fri, 3 May 2019 17:08:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728397AbfECRId (ORCPT ); Fri, 3 May 2019 13:08:33 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:37512 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726391AbfECRIc (ORCPT ); Fri, 3 May 2019 13:08:32 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DC81C15BF; Fri, 3 May 2019 10:08:31 -0700 (PDT) Received: from donnerap.arm.com (donnerap.cambridge.arm.com [10.1.197.44]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 17A273F557; Fri, 3 May 2019 10:08:30 -0700 (PDT) From: Andre Przywara To: Will Deacon Cc: kvm@vger.kernel.org Subject: [PATCH kvmtool 2/2] run: Check for ghost socket file upon VM creation Date: Fri, 3 May 2019 18:08:21 +0100 Message-Id: <20190503170821.260705-3-andre.przywara@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190503170821.260705-1-andre.przywara@arm.com> References: <20190503170821.260705-1-andre.przywara@arm.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Kvmtool creates a (debug) UNIX socket file for each VM, using its (possibly auto-generated) name as the filename. There is a check using access(), which bails out with an error message if a socket with that name already exists. Aside from this check being unnecessary, as the bind() call later would complain as well, this is also racy. But more annoyingly the bail out is not needed most of the time: an existing socket inode is most likely just an orphaned leftover from a previous kvmtool run, which just failed to remove that file, because of a crash, for instance. Upon finding such a collision, let's first try to connect to that socket, to detect if there is still a kvmtool instance listening on the other end. If that fails, this socket will never come back to life, so we can safely clean it up and reuse the name for the new guest. However if the connect() succeeds, there is an actual live kvmtool instance using this name, so not proceeding is the only option. This should never happen with the (PID based) automatically generated names, though. This avoids an annoying (and not helpful) error message and helps automated kvmtool runs to proceed in more cases. Signed-off-by: Andre Przywara --- kvm-ipc.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-) diff --git a/kvm-ipc.c b/kvm-ipc.c index d9a07595..06909171 100644 --- a/kvm-ipc.c +++ b/kvm-ipc.c @@ -43,10 +43,6 @@ static int kvm__create_socket(struct kvm *kvm) snprintf(full_name, sizeof(full_name), "%s/%s%s", kvm__get_dir(), kvm->cfg.guest_name, KVM_SOCK_SUFFIX); - if (access(full_name, F_OK) == 0) { - pr_err("Socket file %s already exist", full_name); - return -EEXIST; - } s = socket(AF_UNIX, SOCK_STREAM, 0); if (s < 0) { @@ -58,6 +54,32 @@ static int kvm__create_socket(struct kvm *kvm) strlcpy(local.sun_path, full_name, sizeof(local.sun_path)); len = strlen(local.sun_path) + sizeof(local.sun_family); r = bind(s, (struct sockaddr *)&local, len); + /* Check for an existing socket file */ + if (r < 0 && errno == EADDRINUSE) { + r = connect(s, (struct sockaddr *)&local, len); + if (r == 0) { + /* + * If we could connect, there is already a guest + * using this same name. This should not happen + * for PID derived names, but could happen for user + * provided guest names. + */ + pr_err("Guest socket file %s already exists.", + full_name); + r = -EEXIST; + goto fail; + } + if (errno == ECONNREFUSED) { + /* + * This is a ghost socket file, with no-one listening + * on the other end. Since kvmtool will only bind + * above when creating a new guest, there is no + * danger in just removing the file and re-trying. + */ + unlink(full_name); + r = bind(s, (struct sockaddr *)&local, len); + } + } if (r < 0) { perror("bind"); goto fail;