From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id A7CF67D2F0 for ; Tue, 30 Jul 2019 15:52:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725974AbfG3Pwg (ORCPT ); Tue, 30 Jul 2019 11:52:36 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:39978 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726910AbfG3Pwf (ORCPT ); Tue, 30 Jul 2019 11:52:35 -0400 Received: by mail-pg1-f193.google.com with SMTP id w10so30285940pgj.7 for ; Tue, 30 Jul 2019 08:52:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=android.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=5nROKYMlxUSQXPN0RUQKtMMM6F4C3uP2jlfRem/QuiY=; b=Mj/6QwoEkcNtMeypMi+v/jC3QqdPjicd27n8XIW2v59C9n/47WcgoL0k3FKs1s8Clm dQiNZTzApteVC/fO/B7/qW/9GmUHzZODlFq+KLGCLjpX/XGaVfk3Cy/dnYcAulRghZ1a tPZ3sQAExYcWjPBC7JhInnR+lgljIV0LcHKsutbvMvHYy5La3SiAPht3ibz6W7ihbFK8 qNWe9Q7agHz0to/y/1LfjZU1hHoXd/YoANapZAQAyMX09PGv7TkLGjpdl1ruFrfEFZOV t6gDcaQAIFtDUs4Ioc1BccSWNoC6cLi1nDZh8RaAwPtaMIwx2eJObkJkW/ByNJ1qNwAl 7J6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=5nROKYMlxUSQXPN0RUQKtMMM6F4C3uP2jlfRem/QuiY=; b=d7+OVvojl2Ehkw46EgringIxqG4GD28IIXCEeguvAGBgdl3dM2Z/g4xnAlUjLBQQG2 IRHihsC6reqVpETu1X9YedtfhLz2UHMGPMGDikwvKBC+9Y+hh7wt8qi6mBFakFIEQQgm OknSm3KcK2pjC8hEqTZuE+WSdpbgwfUteYxDqbQD9uhW/Ay7rdO1ZW2K0dNfQaOvC1e2 gKsy8oYcaTcoPJtB7EPFOUuk/e0Fq3gSYg+y84NkrQ0Uifc2ShAvjVCbCre4m+BBhuZo zZ+fbU/CHfSRlWgp4ECdz0ftL+w6iQehc3RbydwLeZS+cAyU65oWUkyJVNiInX0qI8P4 C6yQ== X-Gm-Message-State: APjAAAUbzfvAlqJvktgGsJpIW3dmGCkkOVgTCs+dImmha7jodA79qRzX BxUNBKBnjdaF1lbYZ1ImVMI= X-Google-Smtp-Source: APXvYqyEmCTaVLfsMONuV6ABrTwjdCMUF6yVY+j8EXIWHssId7BHMydcV6xnYjJlijRKaGjiNrY/YQ== X-Received: by 2002:aa7:8b51:: with SMTP id i17mr43148183pfd.33.1564501954793; Tue, 30 Jul 2019 08:52:34 -0700 (PDT) Received: from nebulus.mtv.corp.google.com ([2620:15c:211:200:5404:91ba:59dc:9400]) by smtp.gmail.com with ESMTPSA id q1sm76758814pfg.84.2019.07.30.08.52.33 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 30 Jul 2019 08:52:34 -0700 (PDT) From: Mark Salyzyn To: linux-kernel@vger.kernel.org Cc: kernel-team@android.com, Mark Salyzyn , Miklos Szeredi , Jonathan Corbet , Vivek Goyal , "Eric W . Biederman" , Amir Goldstein , Randy Dunlap , Stephen Smalley , linux-unionfs@vger.kernel.org, linux-doc@vger.kernel.org Subject: [PATCH v11 0/4] overlayfs override_creds=off Date: Tue, 30 Jul 2019 08:52:21 -0700 Message-Id: <20190730155227.41468-1-salyzyn@android.com> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Patch series: overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh fs: __vfs_getxattr nesting paradigm overlayfs: internal getxattr operations without sepolicy checking overlayfs: override_creds=off option bypass creator_cred The first three patches address fundamental security issues that should be solved regardless of the override_creds=off feature. on them). The fourth adds the feature depends on these other fixes. By default, all access to the upper, lower and work directories is the recorded mounter's MAC and DAC credentials. The incoming accesses are checked against the caller's credentials. If the principles of least privilege are applied for sepolicy, the mounter's credentials might not overlap the credentials of the caller's when accessing the overlayfs filesystem. For example, a file that a lower DAC privileged caller can execute, is MAC denied to the generally higher DAC privileged mounter, to prevent an attack vector. We add the option to turn off override_creds in the mount options; all subsequent operations after mount on the filesystem will be only the caller's credentials. The module boolean parameter and mount option override_creds is also added as a presence check for this "feature", existence of /sys/module/overlay/parameters/overlay_creds Signed-off-by: Mark Salyzyn Cc: Miklos Szeredi Cc: Jonathan Corbet Cc: Vivek Goyal Cc: Eric W. Biederman Cc: Amir Goldstein Cc: Randy Dunlap Cc: Stephen Smalley Cc: linux-unionfs@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- v11: - Squish out v10 introduced patch 2 and 3 in the series, then and use per-thread flag instead for nesting. - Switch name to ovl_do_vds_getxattr for __vds_getxattr wrapper. - Add sb argument to ovl_revert_creds to match future work. v10: - Return NULL on CAP_DAC_READ_SEARCH - Add __get xattr method to solve sepolicy logging issue - Drop unnecessary sys_admin sepolicy checking for administrative driver internal xattr functions. v6: - Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS. - Do better with the documentation, drop rationalizations. - pr_warn message adjusted to report consequences. v5: - beefed up the caveats in the Documentation - Is dependent on "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh" "overlayfs: check CAP_MKNOD before issuing vfs_whiteout" - Added prwarn when override_creds=off v4: - spelling and grammar errors in text v3: - Change name from caller_credentials / creator_credentials to the boolean override_creds. - Changed from creator to mounter credentials. - Updated and fortified the documentation. - Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS v2: - Forward port changed attr to stat, resulting in a build error. - altered commit message.