From patchwork Wed Nov 17 01:58:04 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Anderson X-Patchwork-Id: 12623509 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51B80C4167B for ; Wed, 17 Nov 2021 01:58:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D86661C12 for ; Wed, 17 Nov 2021 01:58:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232666AbhKQCBa (ORCPT ); Tue, 16 Nov 2021 21:01:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232690AbhKQCB3 (ORCPT ); Tue, 16 Nov 2021 21:01:29 -0500 Received: from mail-ua1-x94a.google.com (mail-ua1-x94a.google.com [IPv6:2607:f8b0:4864:20::94a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D389C061767 for ; Tue, 16 Nov 2021 17:58:31 -0800 (PST) Received: by mail-ua1-x94a.google.com with SMTP id n10-20020ab013ca000000b002cfd6ab0ba5so610214uae.1 for ; Tue, 16 Nov 2021 17:58:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:cc; bh=9mdj1xiFilRUGXvU812n33+uRIUP9YX8gtj4fBPRFjw=; b=W8pyuC1HxcZAjVNQCPNCuGecE0cLdPxdG7nuHrxoX9ik7vUw1GQP1Qt7xoBvDBARvH gKntoUZpyj7MbEvph3XSI+fRLv92alGE9XX0Ayq8JNgtxPFh6rmCUjDH5DIeGek1iblS HsIS+6KhO+iB0ujz7bu/jXoJeKwBQOLwZmgAyQCT4BwA3YczvovBxT8CiVIGkfp0bC2Y EpdcqnErSezyZX5hoPOWiv9uej5pYBkgJV1UmC4kVQDZsExCfU1fcctOnJxxx67WDiQg NakanBbHGP4OBoPCwUycj4zFqp1DDtesp7nqK6NMpUF1qLKxQGekG7OpBvAkQsA62N7u Gqig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:cc; bh=9mdj1xiFilRUGXvU812n33+uRIUP9YX8gtj4fBPRFjw=; b=S3u5wQVkQ5UK7joHHrz3scLsHStJw1XzBy3xFtupwlrBp1VEIED4GcPbVgkH2DrNAs jURs42V7fJzig0daWoMLTihnTnT2pgSmZsMXPOcwv2KTOOR+PKeXpWMgZO/ffPoB5WE0 h49AHU5TM+ne9onLPQzqvWCF1Bj/akwJAvP5a6qBrrRnj3zE0n4vjKqpfdqLHc7OjbPv lDldiTWFp79a/1G9LBFUgpR7TIWuSP05/nzn3ToBajMv3Ig3SvC4hjdhmeTNfsqIKm1z VHu7tyx69SSVg2ntk1TA9mUygnhYSIZGa7f14WJcwaj6rmqgd7s+oPClBdGZoxZLowGK e1Nw== X-Gm-Message-State: AOAM533JNZf3jQmOLVkWWphWH+NXYOKfNehs2llCyBz+C5OYAppeRuAv 0quoE9b5dzbQM1QA806Sv3sZLnNswGyw X-Google-Smtp-Source: ABdhPJzOPEJhhk8qQLNAKND//YRmpRQ5IOvlvzPpDzsncg3WQZRB04JIW7X2cz5bx2lTtV30v7/5bmKQKyTX X-Received: from dvandertop.c.googlers.com ([fda3:e722:ac3:cc00:14:4d90:c0a8:2862]) (user=dvander job=sendgmr) by 2002:a05:6122:8d6:: with SMTP id 22mr82551467vkg.21.1637114310621; Tue, 16 Nov 2021 17:58:30 -0800 (PST) Date: Wed, 17 Nov 2021 01:58:04 +0000 In-Reply-To: <20211117015806.2192263-1-dvander@google.com> Message-Id: <20211117015806.2192263-3-dvander@google.com> Mime-Version: 1.0 References: <20211117015806.2192263-1-dvander@google.com> X-Mailer: git-send-email 2.34.0.rc1.387.gb447b232ab-goog Subject: [PATCH v19 2/4] overlayfs: handle XATTR_NOSECURITY flag for get xattr method From: David Anderson Cc: David Anderson , Mark Salyzyn , linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, Stephen Smalley , linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, kernel-team@android.com, Miklos Szeredi , Jonathan Corbet , Vivek Goyal , "Eric W . Biederman" , Amir Goldstein , linux-doc@vger.kernel.org, selinux@vger.kernel.org, paulmoore@microsoft.com, Luca.Boccassi@microsoft.com To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: Because of the overlayfs getxattr recursion, the incoming inode fails to update the selinux sid resulting in avc denials being reported against a target context of u:object_r:unlabeled:s0. Solution is to respond to the XATTR_NOSECURITY flag in get xattr method that calls the __vfs_getxattr handler instead so that the context can be read in, rather than being denied with an -EACCES when vfs_getxattr handler is called. For the use case where access is to be blocked by the security layer. The path then would be security(dentry) -> __vfs_getxattr({dentry...XATTR_NOSECURITY}) -> handler->get({dentry...XATTR_NOSECURITY}) -> __vfs_getxattr({realdentry...XATTR_NOSECURITY}) -> lower_handler->get({realdentry...XATTR_NOSECURITY}) which would report back through the chain data and success as expected, the logging security layer at the top would have the data to determine the access permissions and report back to the logs and the caller that the target context was blocked. For selinux this would solve the cosmetic issue of the selinux log and allow audit2allow to correctly report the rule needed to address the access problem. Check impure, opaque, origin & meta xattr with no sepolicy audit (using __vfs_getxattr) since these operations are internal to overlayfs operations and do not disclose any data. This became an issue for credential override off since sys_admin would have been required by the caller; whereas would have been inherently present for the creator since it performed the mount. This is a change in operations since we do not check in the new ovl_do_getxattr function if the credential override is off or not. Reasoning is that the sepolicy check is unnecessary overhead, especially since the check can be expensive. Because for override credentials off, this affects _everyone_ that underneath performs private xattr calls without the appropriate sepolicy permissions and sys_admin capability. Providing blanket support for sys_admin would be bad for all possible callers. For the override credentials on, this will affect only the mounter, should it lack sepolicy permissions. Not considered a security problem since mounting by definition has sys_admin capabilities, but sepolicy contexts would still need to be crafted. It should be noted that there is precedence, __vfs_getxattr is used in other filesystems for their own internal trusted xattr management. Signed-off-by: Mark Salyzyn Signed-off-by: David Anderson Cc: linux-fsdevel@vger.kernel.org Cc: linux-unionfs@vger.kernel.org Cc: Stephen Smalley Cc: linux-kernel@vger.kernel.org Cc: linux-security-module@vger.kernel.org Cc: kernel-team@android.com Cc: Miklos Szeredi Cc: Jonathan Corbet Cc: Vivek Goyal Cc: Eric W. Biederman Cc: Amir Goldstein Cc: Stephen Smalley Cc: linux-doc@vger.kernel.org Cc: selinux@vger.kernel.org Cc: paulmoore@microsoft.com Cc: Luca.Boccassi@microsoft.com v19 - rebase v18 - correct inode argument to __vfs_getxattr v17 - rebase and add inode argument to __vfs_getxattr v16 - rebase and merge internal getxattr operations patch v15 - revert to v13 because xattr_gs_args rejected. v14 - rebase to use xattr_gs_args. v13 - rebase to use __vfs_getxattr flags option. v12 - Added back to patch series as get xattr with flag option. v11 - Squashed out of patch series and replaced with per-thread flag solution. v10 - Added to patch series as __get xattr method. --- fs/overlayfs/inode.c | 5 +++-- fs/overlayfs/overlayfs.h | 6 ++++-- fs/overlayfs/super.c | 4 ++-- 3 files changed, 9 insertions(+), 6 deletions(-) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 1f36158c7dbe..49bfa33bb682 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -386,7 +386,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name, } int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name, - void *value, size_t size) + void *value, size_t size, int flags) { ssize_t res; const struct cred *old_cred; @@ -394,7 +394,8 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name, ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry); old_cred = ovl_override_creds(dentry->d_sb); - res = vfs_getxattr(&init_user_ns, realdentry, name, value, size); + res = __vfs_getxattr(&init_user_ns, realdentry, d_inode(realdentry), + name, value, size, flags); revert_creds(old_cred); return res; } diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index 2cd5741c873b..3fcd62e72aad 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -187,7 +187,9 @@ static inline ssize_t ovl_do_getxattr(struct ovl_fs *ofs, struct dentry *dentry, size_t size) { const char *name = ovl_xattr(ofs, ox); - int err = vfs_getxattr(&init_user_ns, dentry, name, value, size); + struct inode *ip = d_inode(dentry); + int err = __vfs_getxattr(&init_user_ns, dentry, ip, name, value, size, + XATTR_NOSECURITY); int len = (value && err > 0) ? err : 0; pr_debug("getxattr(%pd2, \"%s\", \"%*pE\", %zu, 0) = %i\n", @@ -496,7 +498,7 @@ int ovl_permission(struct user_namespace *mnt_userns, struct inode *inode, int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name, const void *value, size_t size, int flags); int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name, - void *value, size_t size); + void *value, size_t size, int flags); ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size); struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu); int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags); diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 359aa5772cb7..973644af1288 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1006,7 +1006,7 @@ ovl_posix_acl_xattr_get(const struct xattr_handler *handler, struct dentry *dentry, struct inode *inode, const char *name, void *buffer, size_t size, int flags) { - return ovl_xattr_get(dentry, inode, handler->name, buffer, size); + return ovl_xattr_get(dentry, inode, handler->name, buffer, size, flags); } static int __maybe_unused @@ -1087,7 +1087,7 @@ static int ovl_other_xattr_get(const struct xattr_handler *handler, const char *name, void *buffer, size_t size, int flags) { - return ovl_xattr_get(dentry, inode, name, buffer, size); + return ovl_xattr_get(dentry, inode, name, buffer, size, flags); } static int ovl_other_xattr_set(const struct xattr_handler *handler,