From patchwork Thu Sep 22 15:17:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12985387 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 9F1FAC6FA97 for ; Thu, 22 Sep 2022 15:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232035AbiIVPSw (ORCPT ); Thu, 22 Sep 2022 11:18:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41270 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231879AbiIVPSj (ORCPT ); Thu, 22 Sep 2022 11:18:39 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6416CF0887; Thu, 22 Sep 2022 08:18:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 16F8CB8383E; Thu, 22 Sep 2022 15:18:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B562FC43141; Thu, 22 Sep 2022 15:18:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1663859890; bh=khd9yJ9DVSHAbKI1RnSSMhQz9ZvYIsRT5tFSI3pyVgQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t4WiSmLJs8jmGiRs/bzrpEmaKuMczu/hGlxaNzlppiuT/Qlflz6IVfC0npDC8AlH8 jz/nvGSPjveqXPbT2sGtUgvaCCt7epcXVn295MpTmRpnjkgnvLMJgU34T6vXHDfXBg 99e6ccOh0vJliCLrdyxJaIs5eu66RYJA9m49otxuJW67Hp8ErEZFoVO84Bp95lZSWA ebpXrtQR9/oXn68czRGi52aLHtywcOPXU4uhIK8jJyCXMF1bZq7kSl2ueAbiK26RuX UN+gtuAAQffRkTj47G9ZwC4Uu+QPJB0ZYHoFNM3BL6RVqfG5HebeGmNj77VPpllOdC qHSpI0DFaggAA== From: Christian Brauner To: linux-fsdevel@vger.kernel.org Cc: Christian Brauner , Seth Forshee , Christoph Hellwig , Al Viro , linux-integrity@vger.kernel.org, Paul Moore , Stephen Smalley , Eric Paris , selinux@vger.kernel.org Subject: [PATCH 10/29] selinux: implement set acl hook Date: Thu, 22 Sep 2022 17:17:08 +0200 Message-Id: <20220922151728.1557914-11-brauner@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220922151728.1557914-1-brauner@kernel.org> References: <20220922151728.1557914-1-brauner@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2967; i=brauner@kernel.org; h=from:subject; bh=khd9yJ9DVSHAbKI1RnSSMhQz9ZvYIsRT5tFSI3pyVgQ=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMSTr1FT4Lfn0pZZ14x+uVeaP61mkfb9+YU9b+e/oL97yOxMs bLz2dJSyMIhxMciKKbI4tJuEyy3nqdhslKkBM4eVCWQIAxenAEyEbQkjwxSlrph/n/+8+fVpbkfG9K pQzd57XHuknp5T3FMwbZO2UCkjwxP5ueKTubYt11xenZv4XMdy+cJjbpdfS4XoOIQHeGcL8AEA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org The current way of setting and getting posix acls through the generic xattr interface is error prone and type unsafe. The vfs needs to interpret and fixup posix acls before storing or reporting it to userspace. Various hacks exist to make this work. The code is hard to understand and difficult to maintain in it's current form. Instead of making this work by hacking posix acls through xattr handlers we are building a dedicated posix acl api around the get and set inode operations. This removes a lot of hackiness and makes the codepaths easier to maintain. A lot of background can be found in [1]. So far posix acls were passed as a void blob to the security and integrity modules. Some of them like evm then proceed to interpret the void pointer and convert it into the kernel internal struct posix acl representation to perform their integrity checking magic. This is obviously pretty problematic as that requires knowledge that only the vfs is guaranteed to have and has lead to various bugs. Add a proper security hook for setting posix acls and pass down the posix acls in their appropriate vfs format instead of hacking it through a void pointer stored in the uapi format. I spent considerate time in the security module infrastructure and audited all codepaths. SELinux has no restrictions based on the posix acl values passed through it. The capability hook doesn't need to be called either because it only has restrictions on security.* xattrs. So this all becomes a very simple hook for SELinux. Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Signed-off-by: Christian Brauner (Microsoft) --- security/selinux/hooks.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 79573504783b..bbc0ce3bde35 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3239,6 +3239,13 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns, &ad); } +static int selinux_inode_set_acl(struct user_namespace *mnt_userns, + struct dentry *dentry, const char *acl_name, + struct posix_acl *kacl) +{ + return dentry_has_perm(current_cred(), dentry, FILE__SETATTR); +} + static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags) @@ -7063,6 +7070,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(inode_getxattr, selinux_inode_getxattr), LSM_HOOK_INIT(inode_listxattr, selinux_inode_listxattr), LSM_HOOK_INIT(inode_removexattr, selinux_inode_removexattr), + LSM_HOOK_INIT(inode_set_acl, selinux_inode_set_acl), LSM_HOOK_INIT(inode_getsecurity, selinux_inode_getsecurity), LSM_HOOK_INIT(inode_setsecurity, selinux_inode_setsecurity), LSM_HOOK_INIT(inode_listsecurity, selinux_inode_listsecurity),