From nobody Mon Feb 9 09:15:54 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1588342099; cv=none; d=zohomail.com; s=zohoarc; b=JvjfJbgjB9BEiRPMIRLNEf3e+/0xKKAFB2DPZI1MHnYpFfe91vfIDvqGzGKOsSHz6J2vqCFblOWHAIW1iUlWsKduo+spB8EJ3usrvTES88H3uqU1y6J2Honf4MuhVknZ5omPTtsmim/r4/MLW3AUEh88cPjjn9uoGb6oud1oEyM= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1588342099; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=rkvF79RrRX5S1GUW/qd4mrdcGIbSvsNKlW8sbMYtD+k=; b=RHQxBvcvsuomGnW2apaauoRNUhBGD7vSmEHWA+sRhsAIKEb6G6Io5ag07OxjPXm6g9hZzVCRI68d3aTWsb5yXCstCZNOtc2Ogv7RB7tQxKuLR7b0EMhQaxtUpdkiEasmv2XVTHwNtVYNhgQA8NbM+jGkwgYRTqHGi1WPOFb3kjE= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1588342099295521.5780344315305; Fri, 1 May 2020 07:08:19 -0700 (PDT) Received: from localhost ([::1]:47248 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jUWKv-00041I-TD for importer@patchew.org; Fri, 01 May 2020 10:08:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37290) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jUWK6-0002hj-6i for qemu-devel@nongnu.org; Fri, 01 May 2020 10:07:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jUWK4-0006Iw-5l for qemu-devel@nongnu.org; Fri, 01 May 2020 10:07:25 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:56530 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jUWK3-0006FY-L1 for qemu-devel@nongnu.org; Fri, 01 May 2020 10:07:23 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-50-SzHfc6M1NuuzTT3pXhi7Jw-1; Fri, 01 May 2020 10:07:20 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 865628015D1; Fri, 1 May 2020 14:07:19 +0000 (UTC) Received: from localhost (ovpn-112-36.ams2.redhat.com [10.36.112.36]) by smtp.corp.redhat.com (Postfix) with ESMTP id 32E7E5D9CC; Fri, 1 May 2020 14:07:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588342042; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rkvF79RrRX5S1GUW/qd4mrdcGIbSvsNKlW8sbMYtD+k=; b=Z1M+fThtkel0fCn249tWQh32GlYLhIyolPynoVZO/JYTZjumR0wNdvlAzpuU2iZK+9AGJw WlO66XUu8a3P0cIdU+zJrMNnogCbkfRHGWoNOXzxShj0lZ7U9fgnpowugoN0KpsTqL8sIu KCXdSlCy/Fbpk4C6ZALl6hpaY/e4K3c= X-MC-Unique: SzHfc6M1NuuzTT3pXhi7Jw-1 From: Stefan Hajnoczi To: Subject: [PATCH v2 2/2] virtiofsd: stay below fs.file-max sysctl value (CVE-2020-10717) Date: Fri, 1 May 2020 15:06:44 +0100 Message-Id: <20200501140644.220940-3-stefanha@redhat.com> In-Reply-To: <20200501140644.220940-1-stefanha@redhat.com> References: <20200501140644.220940-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=205.139.110.120; envelope-from=stefanha@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/01 08:22:51 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Dr. David Alan Gilbert" , virtio-fs@redhat.com, Stefan Hajnoczi , Yuval Avrahami , pjp@redhat.com, vgoyal@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" The system-wide fs.file-max sysctl value determines how many files can be open. It defaults to a value calculated based on the machine's RAM size. Previously virtiofsd would try to set RLIMIT_NOFILE to 1,000,000 and this allowed the FUSE client to exhaust the number of open files system-wide on Linux hosts with less than 10 GB of RAM! Take fs.file-max into account when choosing the default RLIMIT_NOFILE value. Fixes: CVE-2020-10717 Reported-by: Yuval Avrahami Signed-off-by: Stefan Hajnoczi Reviewed-by: Dr. David Alan Gilbert --- tools/virtiofsd/helper.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c index dc59f38af0..00a1ef666a 100644 --- a/tools/virtiofsd/helper.c +++ b/tools/virtiofsd/helper.c @@ -176,7 +176,8 @@ void fuse_cmdline_help(void) " default: no_xattr\n" " --rlimit-nofile=3D set maximum number of file de= scriptors\n" " (0 leaves rlimit unchanged)\n" - " default: 1,000,000 if the curre= nt rlimit is lower\n" + " default: min(1000000, fs.file-m= ax - 16384)\n" + " if the current rlimit = is lower\n" ); } =20 @@ -199,9 +200,32 @@ static int fuse_helper_opt_proc(void *data, const char= *arg, int key, =20 static unsigned long get_default_rlimit_nofile(void) { + g_autofree gchar *file_max_str =3D NULL; + const rlim_t reserved_fds =3D 16384; /* leave at least this many fds f= ree */ rlim_t max_fds =3D 1000000; /* our default RLIMIT_NOFILE target */ + rlim_t file_max; struct rlimit rlim; =20 + /* + * Reduce max_fds below the system-wide maximum, if necessary. This + * ensures there are fds available for other processes so we don't + * cause resource exhaustion. + */ + if (!g_file_get_contents("/proc/sys/fs/file-max", &file_max_str, + NULL, NULL)) { + fuse_log(FUSE_LOG_ERR, "can't read /proc/sys/fs/file-max\n"); + exit(1); + } + file_max =3D g_ascii_strtoull(file_max_str, NULL, 10); + if (file_max < 2 * reserved_fds) { + fuse_log(FUSE_LOG_ERR, + "The fs.file-max sysctl is too low (%lu) to allow a " + "reasonable number of open files.\n", + (unsigned long)file_max); + exit(1); + } + max_fds =3D MIN(file_max - reserved_fds, max_fds); + if (getrlimit(RLIMIT_NOFILE, &rlim) < 0) { fuse_log(FUSE_LOG_ERR, "getrlimit(RLIMIT_NOFILE): %m\n"); exit(1); --=20 2.25.3