From patchwork Thu Nov 3 15:12:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ondrej Mosnacek X-Patchwork-Id: 13030233 X-Patchwork-Delegate: paul@paul-moore.com 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4960EC4332F for ; Thu, 3 Nov 2022 15:13:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231320AbiKCPNf (ORCPT ); Thu, 3 Nov 2022 11:13:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53674 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231909AbiKCPNb (ORCPT ); Thu, 3 Nov 2022 11:13:31 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7761E1ADB3 for ; Thu, 3 Nov 2022 08:12:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667488329; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=LWgxR1F68mKVnmdpW8+jJqPrx2L99twB8sOEHi9u21s=; b=KqHPDHs2Ab3SdL/GTizlW/OdhpjWhEbvGCv1FDX1mYrd1GE4vYx5O4oqrjCXhSRP1l6iND iEu1YyqCXbGEQRQwnE0hyjSxFt3m3jR2EAg7dKDXHU0cGcE1zd+x1pZmuc2ziR6PVDBN5/ +dWLz2I5tkFfrMUZZON7hi5CDoJSoJY= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-650-eMlJu19KMWy80GliMXp-_g-1; Thu, 03 Nov 2022 11:12:08 -0400 X-MC-Unique: eMlJu19KMWy80GliMXp-_g-1 Received: by mail-wr1-f72.google.com with SMTP id d10-20020adfa34a000000b00236616a168bso595337wrb.18 for ; Thu, 03 Nov 2022 08:12:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=LWgxR1F68mKVnmdpW8+jJqPrx2L99twB8sOEHi9u21s=; b=UZeb/v33D1Evbtht+0XEDXDcZBP9tdHz+7x8arMBmB7aMjGGYPQQUgbPBaWF3lNCKs 7ek/eRgS7m2aQZcMzQMUIP1x1CUrbLZNKF3GbM3ASCu0/IUdSedjV1LKYw0sSj6VsMc3 O7Ta3YwEoJ4wJKWDhVdzvWZmSeFJgnl4UuWKomDz0fdk54hVwO8AKWA7TbmaZj0TEpsh hw1iKOY2MeJHqqh3tz0XY7ICqT6/8Fdz/hijXsAX/SBRE/gM3uTX8G81sdum1DcWxscL 85j9Aq7aoIxurfMWU9PQTXcOZWSx7FoBimYsm/KWXuDaWp+l8mH1Odp/mTfWait8fgiI KuJw== X-Gm-Message-State: ACrzQf0U/OdJMnSOq7iacDPipAYq8b31FdHCySx9cuPI6ntUFpDuDHm0 DJrfPkjp68agdu5EYQZItiPVX55NK/A9NhYgJu9cvBiHakl5d9ZNA3ItuXTUqcndO8zAIbRsDxB VSZQBbdIb+T2DkjFlmw== X-Received: by 2002:a05:600c:3655:b0:3cf:7082:dc18 with SMTP id y21-20020a05600c365500b003cf7082dc18mr15530765wmq.36.1667488327464; Thu, 03 Nov 2022 08:12:07 -0700 (PDT) X-Google-Smtp-Source: AMsMyM5ux4jknt5HP+aYQrcIxkNpUyABfRNH3oJZnAwXDcMOJ+KB7r/Wfbv+pV7I7knZb9J+AiUzmQ== X-Received: by 2002:a05:600c:3655:b0:3cf:7082:dc18 with SMTP id y21-20020a05600c365500b003cf7082dc18mr15530746wmq.36.1667488327247; Thu, 03 Nov 2022 08:12:07 -0700 (PDT) Received: from localhost.localdomain (nat-pool-brq-t.redhat.com. [213.175.37.10]) by smtp.gmail.com with ESMTPSA id v4-20020a5d6784000000b00235da296623sm1104080wru.31.2022.11.03.08.12.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 08:12:06 -0700 (PDT) From: Ondrej Mosnacek To: Alexander Viro Cc: linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-kernel@vger.kernel.org, Martin Pitt , Christian Brauner Subject: [PATCH v2] fs: don't audit the capability check in simple_xattr_list() Date: Thu, 3 Nov 2022 16:12:05 +0100 Message-Id: <20221103151205.702826-1-omosnace@redhat.com> X-Mailer: git-send-email 2.38.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org The check being unconditional may lead to unwanted denials reported by LSMs when a process has the capability granted by DAC, but denied by an LSM. In the case of SELinux such denials are a problem, since they can't be effectively filtered out via the policy and when not silenced, they produce noise that may hide a true problem or an attack. Checking for the capability only if any trusted xattr is actually present wouldn't really address the issue, since calling listxattr(2) on such node on its own doesn't indicate an explicit attempt to see the trusted xattrs. Additionally, it could potentially leak the presence of trusted xattrs to an unprivileged user if they can check for the denials (e.g. through dmesg). Therefore, it's best (and simplest) to keep the check unconditional and instead use ns_capable_noaudit() that will silence any associated LSM denials. Fixes: 38f38657444d ("xattr: extract simple_xattr code from tmpfs") Reported-by: Martin Pitt Suggested-by: Christian Brauner (Microsoft) Signed-off-by: Ondrej Mosnacek Reviewed-by: Christian Brauner (Microsoft) Reviewed-by: Paul Moore --- v1 -> v2: switch to simpler and better solution as suggested by Christian v1: https://lore.kernel.org/selinux/CAFqZXNuC7c0Ukx_okYZ7rsKycQY5P1zpMPmmq_T5Qyzbg-x7yQ@mail.gmail.com/T/ fs/xattr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/xattr.c b/fs/xattr.c index 61107b6bbed2..427b8cea1f96 100644 --- a/fs/xattr.c +++ b/fs/xattr.c @@ -1140,7 +1140,7 @@ static int xattr_list_one(char **buffer, ssize_t *remaining_size, ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs, char *buffer, size_t size) { - bool trusted = capable(CAP_SYS_ADMIN); + bool trusted = ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN); struct simple_xattr *xattr; ssize_t remaining_size = size; int err = 0;