From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8089CC43387 for ; Wed, 16 Jan 2019 16:10:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FEDF205C9 for ; Wed, 16 Jan 2019 16:10:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=yahoo.com header.i=@yahoo.com header.b="KTo80jTP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727383AbfAPQKi (ORCPT ); Wed, 16 Jan 2019 11:10:38 -0500 Received: from sonic313-16.consmr.mail.ne1.yahoo.com ([66.163.185.39]:32789 "EHLO sonic313-16.consmr.mail.ne1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726917AbfAPQKi (ORCPT ); Wed, 16 Jan 2019 11:10:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s2048; t=1547655028; bh=+o1VVmYjlvV9lzzi96dQ3ulKq4Yzoybh59jO7efA7xI=; h=Subject:To:References:From:Date:In-Reply-To:From:Subject; b=KTo80jTPRIvlKlq9TNF9Vu/z96gC6oiQDHBOGoz2cuDenzjg6jh7Xn8UvXi9T2xutYU+/ftME36nmlujjq0LW/BeZwKy5mlyY6Fc8SANOezAus6/SoYGIU6WqOxRaJlU//OSZ52CJVXrZFRK1QbwOHbzl8k9tu9pA3ZALzwH8NHfLKQV833BsWfeu3z7QlS4fD1AXoYKSr4BnRTS1m9XAh98WlFzNB/VYLPcp+4lhmXPBUbzLZaNkUHfl+1J/dG3OVk7Z3p+QXeu1ospAtg1Ssu4r+6rFiPHNHRgm10SSd6+yUSHy8Oqk/uFXidhujqZT095MK1T9QYPsbH+SPQGgQ== X-YMail-OSG: MozrToEVM1mY06W__nFKIb4cpOoaQEFXUUV.Q206x1M3DAgrF9pX1IoRHgLDVCR Fu7hoIjbXuHCrHYtGMKQ9UBywrq_sqYKSdyarfho3OlXeYiEbUKMJSTn9px8wwdnEoWXcmVpPI_I gc9nfAgF2e0vERbuo.AzIvi6y5qgn8syN2ltcwu0pN5sBhpxgGmnqsWV1KWr2EDnev4bKh53Lvpf wYcBMXzbA.cryyGQOiYm5s33WfvzbD89dyV43gnBaDIwlPQKoiB2izs3bLG5gs5bZ06FaVaKM7rP qhEs4c.m5Sv5KIr8aJdWuJfQ.jn4OIMh4EaUqpK8o_co1A91OjJCnc6hYyrNVdVDu4ei_gePRpUf jqowD1HZIfXPyW8IHuE7j1CAngqbw9UGPHVvYLEuIy3CK6STEGl0JPsmLVRQqrXzTXnt8eff3BXn k.qYMSwAy8ds6A49PzUnOxzIUm6kfURQB5ODnNcUo5aGUNsGX1r_xegrGMdtI53dGQFuG8CCyJQ3 pM1kE0lt254H4CAK96La7Pe4rqhbzvqQU4zXa4CEynoLxG4tTRPika_ZBxQWbqC3n1nvL2XNOkyB ._KXMyakfv5UHwbet.CMxXptehvLjOMk3sLG.9M4oeXyZ0MYva9gONgORM4InbLoT3ECxXww25yd DCP3NkQngMTnNuQ05g65BKJsIjyUvzfXwoCkuOMVdjKSiMky.opw34QZtDmuW0Vg5f9FsiNcv6iB QFT55yNPk49G6kbtjpse42NsK4VeUyWtED4y5G6_6v3Yy_262RdEg_whBDRN.DHmDhqJpQic64Ff _riIy.w8t8_VAcBF1kcnohfeAGA7ffJTkt5VQoR_CEEZfNMKY8yDBCYOIWQahdyO0VJvRwGJnhhd TnX.fCruwMGO7xOLgKBVfgATWUitXsUuesF7qtTc3Ke2D1jhYRihu_niUeVSB6.j2_yIC_QFA1.D cReDsUR5ksorP3RdH0547GBFd1YLcvSQOQsupHTbUJKE2RWs6nPKk7HG8GSrqLlvbr5XLOg8Pptt sGwCheqUIQREdZP27_KHEsqZaPVnXc3JtDAY9l8ntxFes5U4PYQ0ySXfqNsXzOq.b82edTVWbejQ Xo.9i2dYL69GXzIe2TY34le69LWCX Received: from sonic.gate.mail.ne1.yahoo.com by sonic313.consmr.mail.ne1.yahoo.com with HTTP; Wed, 16 Jan 2019 16:10:28 +0000 Received: from c-67-169-65-224.hsd1.ca.comcast.net (EHLO [192.168.0.102]) ([67.169.65.224]) by smtp420.mail.ne1.yahoo.com (Oath Hermes SMTP Server) with ESMTPA ID 38ff7474c14d01a60fb57d2f39d6d42a; Wed, 16 Jan 2019 16:10:24 +0000 (UTC) Subject: Re: [PATCH v5 2/2] LSM: add SafeSetID module that gates setid calls To: mortonm@chromium.org, jmorris@namei.org, serge@hallyn.com, keescook@chromium.org, sds@tycho.nsa.gov, linux-security-module@vger.kernel.org References: <20190116154606.92331-1-mortonm@chromium.org> From: Casey Schaufler Message-ID: <59075206-784c-3225-4150-0c6e2c319083@schaufler-ca.com> Date: Wed, 16 Jan 2019 08:10:16 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190116154606.92331-1-mortonm@chromium.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 1/16/2019 7:46 AM, mortonm@chromium.org wrote: > From: Micah Morton > > SafeSetID gates the setid family of syscalls to restrict UID/GID > transitions from a given UID/GID to only those approved by a > system-wide whitelist. These restrictions also prohibit the given > UIDs/GIDs from obtaining auxiliary privileges associated with > CAP_SET{U/G}ID, such as allowing a user to set up user namespace UID > mappings. For now, only gating the set*uid family of syscalls is > supported, with support for set*gid coming in a future patch set. > > Signed-off-by: Micah Morton > Acked-by: Kees Cook While I have some lesser reservations philosophically, all direct technical objections have been addressed. Acked-by: Casey Schaufler > --- > Changes since last patch: > - added 'safesetid' to the ordered list of enabled LSMs in > security/Kconfig. > - added a "did I get initialized?" variable for the securityfs init to > check and check that variable in securityfs.c to skip tree creation > if safesetid isn't running > Documentation/admin-guide/LSM/SafeSetID.rst | 107 ++++++++ > Documentation/admin-guide/LSM/index.rst | 1 + > security/Kconfig | 3 +- > security/Makefile | 2 + > security/safesetid/Kconfig | 12 + > security/safesetid/Makefile | 7 + > security/safesetid/lsm.c | 277 ++++++++++++++++++++ > security/safesetid/lsm.h | 33 +++ > security/safesetid/securityfs.c | 193 ++++++++++++++ > 9 files changed, 634 insertions(+), 1 deletion(-) > create mode 100644 Documentation/admin-guide/LSM/SafeSetID.rst > create mode 100644 security/safesetid/Kconfig > create mode 100644 security/safesetid/Makefile > create mode 100644 security/safesetid/lsm.c > create mode 100644 security/safesetid/lsm.h > create mode 100644 security/safesetid/securityfs.c > > diff --git a/Documentation/admin-guide/LSM/SafeSetID.rst b/Documentation/admin-guide/LSM/SafeSetID.rst > new file mode 100644 > index 000000000000..ffb64be67f7a > --- /dev/null > +++ b/Documentation/admin-guide/LSM/SafeSetID.rst > @@ -0,0 +1,107 @@ > +========= > +SafeSetID > +========= > +SafeSetID is an LSM module that gates the setid family of syscalls to restrict > +UID/GID transitions from a given UID/GID to only those approved by a > +system-wide whitelist. These restrictions also prohibit the given UIDs/GIDs > +from obtaining auxiliary privileges associated with CAP_SET{U/G}ID, such as > +allowing a user to set up user namespace UID mappings. > + > + > +Background > +========== > +In absence of file capabilities, processes spawned on a Linux system that need > +to switch to a different user must be spawned with CAP_SETUID privileges. > +CAP_SETUID is granted to programs running as root or those running as a non-root > +user that have been explicitly given the CAP_SETUID runtime capability. It is > +often preferable to use Linux runtime capabilities rather than file > +capabilities, since using file capabilities to run a program with elevated > +privileges opens up possible security holes since any user with access to the > +file can exec() that program to gain the elevated privileges. > + > +While it is possible to implement a tree of processes by giving full > +CAP_SET{U/G}ID capabilities, this is often at odds with the goals of running a > +tree of processes under non-root user(s) in the first place. Specifically, > +since CAP_SETUID allows changing to any user on the system, including the root > +user, it is an overpowered capability for what is needed in this scenario, > +especially since programs often only call setuid() to drop privileges to a > +lesser-privileged user -- not elevate privileges. Unfortunately, there is no > +generally feasible way in Linux to restrict the potential UIDs that a user can > +switch to through setuid() beyond allowing a switch to any user on the system. > +This SafeSetID LSM seeks to provide a solution for restricting setid > +capabilities in such a way. > + > +The main use case for this LSM is to allow a non-root program to transition to > +other untrusted uids without full blown CAP_SETUID capabilities. The non-root > +program would still need CAP_SETUID to do any kind of transition, but the > +additional restrictions imposed by this LSM would mean it is a "safer" version > +of CAP_SETUID since the non-root program cannot take advantage of CAP_SETUID to > +do any unapproved actions (e.g. setuid to uid 0 or create/enter new user > +namespace). The higher level goal is to allow for uid-based sandboxing of system > +services without having to give out CAP_SETUID all over the place just so that > +non-root programs can drop to even-lesser-privileged uids. This is especially > +relevant when one non-root daemon on the system should be allowed to spawn other > +processes as different uids, but its undesirable to give the daemon a > +basically-root-equivalent CAP_SETUID. > + > + > +Other Approaches Considered > +=========================== > + > +Solve this problem in userspace > +------------------------------- > +For candidate applications that would like to have restricted setid capabilities > +as implemented in this LSM, an alternative option would be to simply take away > +setid capabilities from the application completely and refactor the process > +spawning semantics in the application (e.g. by using a privileged helper program > +to do process spawning and UID/GID transitions). Unfortunately, there are a > +number of semantics around process spawning that would be affected by this, such > +as fork() calls where the program doesn’t immediately call exec() after the > +fork(), parent processes specifying custom environment variables or command line > +args for spawned child processes, or inheritance of file handles across a > +fork()/exec(). Because of this, as solution that uses a privileged helper in > +userspace would likely be less appealing to incorporate into existing projects > +that rely on certain process-spawning semantics in Linux. > + > +Use user namespaces > +------------------- > +Another possible approach would be to run a given process tree in its own user > +namespace and give programs in the tree setid capabilities. In this way, > +programs in the tree could change to any desired UID/GID in the context of their > +own user namespace, and only approved UIDs/GIDs could be mapped back to the > +initial system user namespace, affectively preventing privilege escalation. > +Unfortunately, it is not generally feasible to use user namespaces in isolation, > +without pairing them with other namespace types, which is not always an option. > +Linux checks for capabilities based off of the user namespace that “owns” some > +entity. For example, Linux has the notion that network namespaces are owned by > +the user namespace in which they were created. A consequence of this is that > +capability checks for access to a given network namespace are done by checking > +whether a task has the given capability in the context of the user namespace > +that owns the network namespace -- not necessarily the user namespace under > +which the given task runs. Therefore spawning a process in a new user namespace > +effectively prevents it from accessing the network namespace owned by the > +initial namespace. This is a deal-breaker for any application that expects to > +retain the CAP_NET_ADMIN capability for the purpose of adjusting network > +configurations. Using user namespaces in isolation causes problems regarding > +other system interactions, including use of pid namespaces and device creation. > + > +Use an existing LSM > +------------------- > +None of the other in-tree LSMs have the capability to gate setid transitions, or > +even employ the security_task_fix_setuid hook at all. SELinux says of that hook: > +"Since setuid only affects the current process, and since the SELinux controls > +are not based on the Linux identity attributes, SELinux does not need to control > +this operation." > + > + > +Directions for use > +================== > +This LSM hooks the setid syscalls to make sure transitions are allowed if an > +applicable restriction policy is in place. Policies are configured through > +securityfs by writing to the safesetid/add_whitelist_policy and > +safesetid/flush_whitelist_policies files at the location where securityfs is > +mounted. The format for adding a policy is ':', using literal > +numbers, such as '123:456'. To flush the policies, any write to the file is > +sufficient. Again, configuring a policy for a UID will prevent that UID from > +obtaining auxiliary setid privileges, such as allowing a user to set up user > +namespace UID mappings. > diff --git a/Documentation/admin-guide/LSM/index.rst b/Documentation/admin-guide/LSM/index.rst > index 9842e21afd4a..a6ba95fbaa9f 100644 > --- a/Documentation/admin-guide/LSM/index.rst > +++ b/Documentation/admin-guide/LSM/index.rst > @@ -46,3 +46,4 @@ subdirectories. > Smack > tomoyo > Yama > + SafeSetID > diff --git a/security/Kconfig b/security/Kconfig > index 78dc12b7eeb3..9555f4914492 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -236,12 +236,13 @@ source "security/tomoyo/Kconfig" > source "security/apparmor/Kconfig" > source "security/loadpin/Kconfig" > source "security/yama/Kconfig" > +source "security/safesetid/Kconfig" > > source "security/integrity/Kconfig" > > config LSM > string "Ordered list of enabled LSMs" > - default "yama,loadpin,integrity,selinux,smack,tomoyo,apparmor" > + default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" > help > A comma-separated list of LSMs, in initialization order. > Any LSMs left off this list will be ignored. This can be > diff --git a/security/Makefile b/security/Makefile > index 4d2d3782ddef..c598b904938f 100644 > --- a/security/Makefile > +++ b/security/Makefile > @@ -10,6 +10,7 @@ subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo > subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor > subdir-$(CONFIG_SECURITY_YAMA) += yama > subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin > +subdir-$(CONFIG_SECURITY_SAFESETID) += safesetid > > # always enable default capabilities > obj-y += commoncap.o > @@ -25,6 +26,7 @@ obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/ > obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/ > obj-$(CONFIG_SECURITY_YAMA) += yama/ > obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/ > +obj-$(CONFIG_SECURITY_SAFESETID) += safesetid/ > obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o > > # Object integrity file lists > diff --git a/security/safesetid/Kconfig b/security/safesetid/Kconfig > new file mode 100644 > index 000000000000..bf89a47ffcc8 > --- /dev/null > +++ b/security/safesetid/Kconfig > @@ -0,0 +1,12 @@ > +config SECURITY_SAFESETID > + bool "Gate setid transitions to limit CAP_SET{U/G}ID capabilities" > + default n > + help > + SafeSetID is an LSM module that gates the setid family of syscalls to > + restrict UID/GID transitions from a given UID/GID to only those > + approved by a system-wide whitelist. These restrictions also prohibit > + the given UIDs/GIDs from obtaining auxiliary privileges associated > + with CAP_SET{U/G}ID, such as allowing a user to set up user namespace > + UID mappings. > + > + If you are unsure how to answer this question, answer N. > diff --git a/security/safesetid/Makefile b/security/safesetid/Makefile > new file mode 100644 > index 000000000000..6b0660321164 > --- /dev/null > +++ b/security/safesetid/Makefile > @@ -0,0 +1,7 @@ > +# SPDX-License-Identifier: GPL-2.0 > +# > +# Makefile for the safesetid LSM. > +# > + > +obj-$(CONFIG_SECURITY_SAFESETID) := safesetid.o > +safesetid-y := lsm.o securityfs.o > diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c > new file mode 100644 > index 000000000000..3a2c75ac810c > --- /dev/null > +++ b/security/safesetid/lsm.c > @@ -0,0 +1,277 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * SafeSetID Linux Security Module > + * > + * Author: Micah Morton > + * > + * Copyright (C) 2018 The Chromium OS Authors. > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2, as > + * published by the Free Software Foundation. > + * > + */ > + > +#define pr_fmt(fmt) "SafeSetID: " fmt > + > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +/* Flag indicating whether initialization completed */ > +int safesetid_initialized; > + > +#define NUM_BITS 8 /* 128 buckets in hash table */ > + > +static DEFINE_HASHTABLE(safesetid_whitelist_hashtable, NUM_BITS); > + > +/* > + * Hash table entry to store safesetid policy signifying that 'parent' user > + * can setid to 'child' user. > + */ > +struct entry { > + struct hlist_node next; > + struct hlist_node dlist; /* for deletion cleanup */ > + uint64_t parent_kuid; > + uint64_t child_kuid; > +}; > + > +static DEFINE_SPINLOCK(safesetid_whitelist_hashtable_spinlock); > + > +static bool check_setuid_policy_hashtable_key(kuid_t parent) > +{ > + struct entry *entry; > + > + rcu_read_lock(); > + hash_for_each_possible_rcu(safesetid_whitelist_hashtable, > + entry, next, __kuid_val(parent)) { > + if (entry->parent_kuid == __kuid_val(parent)) { > + rcu_read_unlock(); > + return true; > + } > + } > + rcu_read_unlock(); > + > + return false; > +} > + > +static bool check_setuid_policy_hashtable_key_value(kuid_t parent, > + kuid_t child) > +{ > + struct entry *entry; > + > + rcu_read_lock(); > + hash_for_each_possible_rcu(safesetid_whitelist_hashtable, > + entry, next, __kuid_val(parent)) { > + if (entry->parent_kuid == __kuid_val(parent) && > + entry->child_kuid == __kuid_val(child)) { > + rcu_read_unlock(); > + return true; > + } > + } > + rcu_read_unlock(); > + > + return false; > +} > + > +static int safesetid_security_capable(const struct cred *cred, > + struct user_namespace *ns, > + int cap, > + unsigned int opts) > +{ > + if (cap == CAP_SETUID && > + check_setuid_policy_hashtable_key(cred->uid)) { > + if (!(opts & CAP_OPT_INSETID)) { > + /* > + * Deny if we're not in a set*uid() syscall to avoid > + * giving powers gated by CAP_SETUID that are related > + * to functionality other than calling set*uid() (e.g. > + * allowing user to set up userns uid mappings). > + */ > + pr_warn("Operation requires CAP_SETUID, which is not available to UID %u for operations besides approved set*uid transitions", > + __kuid_val(cred->uid)); > + return -1; > + } > + } > + return 0; > +} > + > +static int check_uid_transition(kuid_t parent, kuid_t child) > +{ > + if (check_setuid_policy_hashtable_key_value(parent, child)) > + return 0; > + pr_warn("UID transition (%d -> %d) blocked", > + __kuid_val(parent), > + __kuid_val(child)); > + /* > + * Kill this process to avoid potential security vulnerabilities > + * that could arise from a missing whitelist entry preventing a > + * privileged process from dropping to a lesser-privileged one. > + */ > + force_sig(SIGKILL, current); > + return -EACCES; > +} > + > +/* > + * Check whether there is either an exception for user under old cred struct to > + * set*uid to user under new cred struct, or the UID transition is allowed (by > + * Linux set*uid rules) even without CAP_SETUID. > + */ > +static int safesetid_task_fix_setuid(struct cred *new, > + const struct cred *old, > + int flags) > +{ > + > + /* Do nothing if there are no setuid restrictions for this UID. */ > + if (!check_setuid_policy_hashtable_key(old->uid)) > + return 0; > + > + switch (flags) { > + case LSM_SETID_RE: > + /* > + * Users for which setuid restrictions exist can only set the > + * real UID to the real UID or the effective UID, unless an > + * explicit whitelist policy allows the transition. > + */ > + if (!uid_eq(old->uid, new->uid) && > + !uid_eq(old->euid, new->uid)) { > + return check_uid_transition(old->uid, new->uid); > + } > + /* > + * Users for which setuid restrictions exist can only set the > + * effective UID to the real UID, the effective UID, or the > + * saved set-UID, unless an explicit whitelist policy allows > + * the transition. > + */ > + if (!uid_eq(old->uid, new->euid) && > + !uid_eq(old->euid, new->euid) && > + !uid_eq(old->suid, new->euid)) { > + return check_uid_transition(old->euid, new->euid); > + } > + break; > + case LSM_SETID_ID: > + /* > + * Users for which setuid restrictions exist cannot change the > + * real UID or saved set-UID unless an explicit whitelist > + * policy allows the transition. > + */ > + if (!uid_eq(old->uid, new->uid)) > + return check_uid_transition(old->uid, new->uid); > + if (!uid_eq(old->suid, new->suid)) > + return check_uid_transition(old->suid, new->suid); > + break; > + case LSM_SETID_RES: > + /* > + * Users for which setuid restrictions exist cannot change the > + * real UID, effective UID, or saved set-UID to anything but > + * one of: the current real UID, the current effective UID or > + * the current saved set-user-ID unless an explicit whitelist > + * policy allows the transition. > + */ > + if (!uid_eq(new->uid, old->uid) && > + !uid_eq(new->uid, old->euid) && > + !uid_eq(new->uid, old->suid)) { > + return check_uid_transition(old->uid, new->uid); > + } > + if (!uid_eq(new->euid, old->uid) && > + !uid_eq(new->euid, old->euid) && > + !uid_eq(new->euid, old->suid)) { > + return check_uid_transition(old->euid, new->euid); > + } > + if (!uid_eq(new->suid, old->uid) && > + !uid_eq(new->suid, old->euid) && > + !uid_eq(new->suid, old->suid)) { > + return check_uid_transition(old->suid, new->suid); > + } > + break; > + case LSM_SETID_FS: > + /* > + * Users for which setuid restrictions exist cannot change the > + * filesystem UID to anything but one of: the current real UID, > + * the current effective UID or the current saved set-UID > + * unless an explicit whitelist policy allows the transition. > + */ > + if (!uid_eq(new->fsuid, old->uid) && > + !uid_eq(new->fsuid, old->euid) && > + !uid_eq(new->fsuid, old->suid) && > + !uid_eq(new->fsuid, old->fsuid)) { > + return check_uid_transition(old->fsuid, new->fsuid); > + } > + break; > + default: > + pr_warn("Unknown setid state %d\n", flags); > + force_sig(SIGKILL, current); > + return -EINVAL; > + } > + return 0; > +} > + > +int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child) > +{ > + struct entry *new; > + > + /* Return if entry already exists */ > + if (check_setuid_policy_hashtable_key_value(parent, child)) > + return 0; > + > + new = kzalloc(sizeof(struct entry), GFP_KERNEL); > + if (!new) > + return -ENOMEM; > + new->parent_kuid = __kuid_val(parent); > + new->child_kuid = __kuid_val(child); > + spin_lock(&safesetid_whitelist_hashtable_spinlock); > + hash_add_rcu(safesetid_whitelist_hashtable, > + &new->next, > + __kuid_val(parent)); > + spin_unlock(&safesetid_whitelist_hashtable_spinlock); > + return 0; > +} > + > +void flush_safesetid_whitelist_entries(void) > +{ > + struct entry *entry; > + struct hlist_node *hlist_node; > + unsigned int bkt_loop_cursor; > + HLIST_HEAD(free_list); > + > + /* > + * Could probably use hash_for_each_rcu here instead, but this should > + * be fine as well. > + */ > + spin_lock(&safesetid_whitelist_hashtable_spinlock); > + hash_for_each_safe(safesetid_whitelist_hashtable, bkt_loop_cursor, > + hlist_node, entry, next) { > + hash_del_rcu(&entry->next); > + hlist_add_head(&entry->dlist, &free_list); > + } > + spin_unlock(&safesetid_whitelist_hashtable_spinlock); > + synchronize_rcu(); > + hlist_for_each_entry_safe(entry, hlist_node, &free_list, dlist) { > + hlist_del(&entry->dlist); > + kfree(entry); > + } > +} > + > +static struct security_hook_list safesetid_security_hooks[] = { > + LSM_HOOK_INIT(task_fix_setuid, safesetid_task_fix_setuid), > + LSM_HOOK_INIT(capable, safesetid_security_capable) > +}; > + > +static int __init safesetid_security_init(void) > +{ > + security_add_hooks(safesetid_security_hooks, > + ARRAY_SIZE(safesetid_security_hooks), "safesetid"); > + > + /* Report that SafeSetID successfully initialized */ > + safesetid_initialized = 1; > + > + return 0; > +} > + > +DEFINE_LSM(safesetid_security_init) = { > + .init = safesetid_security_init, > +}; > diff --git a/security/safesetid/lsm.h b/security/safesetid/lsm.h > new file mode 100644 > index 000000000000..c1ea3c265fcf > --- /dev/null > +++ b/security/safesetid/lsm.h > @@ -0,0 +1,33 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * SafeSetID Linux Security Module > + * > + * Author: Micah Morton > + * > + * Copyright (C) 2018 The Chromium OS Authors. > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2, as > + * published by the Free Software Foundation. > + * > + */ > +#ifndef _SAFESETID_H > +#define _SAFESETID_H > + > +#include > + > +/* Flag indicating whether initialization completed */ > +extern int safesetid_initialized; > + > +/* Function type. */ > +enum safesetid_whitelist_file_write_type { > + SAFESETID_WHITELIST_ADD, /* Add whitelist policy. */ > + SAFESETID_WHITELIST_FLUSH, /* Flush whitelist policies. */ > +}; > + > +/* Add entry to safesetid whitelist to allow 'parent' to setid to 'child'. */ > +int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child); > + > +void flush_safesetid_whitelist_entries(void); > + > +#endif /* _SAFESETID_H */ > diff --git a/security/safesetid/securityfs.c b/security/safesetid/securityfs.c > new file mode 100644 > index 000000000000..61be4ee459cc > --- /dev/null > +++ b/security/safesetid/securityfs.c > @@ -0,0 +1,193 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * SafeSetID Linux Security Module > + * > + * Author: Micah Morton > + * > + * Copyright (C) 2018 The Chromium OS Authors. > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License version 2, as > + * published by the Free Software Foundation. > + * > + */ > +#include > +#include > + > +#include "lsm.h" > + > +static struct dentry *safesetid_policy_dir; > + > +struct safesetid_file_entry { > + const char *name; > + enum safesetid_whitelist_file_write_type type; > + struct dentry *dentry; > +}; > + > +static struct safesetid_file_entry safesetid_files[] = { > + {.name = "add_whitelist_policy", > + .type = SAFESETID_WHITELIST_ADD}, > + {.name = "flush_whitelist_policies", > + .type = SAFESETID_WHITELIST_FLUSH}, > +}; > + > +/* > + * In the case the input buffer contains one or more invalid UIDs, the kuid_t > + * variables pointed to by 'parent' and 'child' will get updated but this > + * function will return an error. > + */ > +static int parse_safesetid_whitelist_policy(const char __user *buf, > + size_t len, > + kuid_t *parent, > + kuid_t *child) > +{ > + char *kern_buf; > + char *parent_buf; > + char *child_buf; > + const char separator[] = ":"; > + int ret; > + size_t first_substring_length; > + long parsed_parent; > + long parsed_child; > + > + /* Duplicate string from user memory and NULL-terminate */ > + kern_buf = memdup_user_nul(buf, len); > + if (IS_ERR(kern_buf)) > + return PTR_ERR(kern_buf); > + > + /* > + * Format of |buf| string should be :. > + * Find location of ":" in kern_buf (copied from |buf|). > + */ > + first_substring_length = strcspn(kern_buf, separator); > + if (first_substring_length == 0 || first_substring_length == len) { > + ret = -EINVAL; > + goto free_kern; > + } > + > + parent_buf = kmemdup_nul(kern_buf, first_substring_length, GFP_KERNEL); > + if (!parent_buf) { > + ret = -ENOMEM; > + goto free_kern; > + } > + > + ret = kstrtol(parent_buf, 0, &parsed_parent); > + if (ret) > + goto free_both; > + > + child_buf = kern_buf + first_substring_length + 1; > + ret = kstrtol(child_buf, 0, &parsed_child); > + if (ret) > + goto free_both; > + > + *parent = make_kuid(current_user_ns(), parsed_parent); > + if (!uid_valid(*parent)) { > + ret = -EINVAL; > + goto free_both; > + } > + > + *child = make_kuid(current_user_ns(), parsed_child); > + if (!uid_valid(*child)) { > + ret = -EINVAL; > + goto free_both; > + } > + > +free_both: > + kfree(parent_buf); > +free_kern: > + kfree(kern_buf); > + return ret; > +} > + > +static ssize_t safesetid_file_write(struct file *file, > + const char __user *buf, > + size_t len, > + loff_t *ppos) > +{ > + struct safesetid_file_entry *file_entry = > + file->f_inode->i_private; > + kuid_t parent; > + kuid_t child; > + int ret; > + > + if (!ns_capable(current_user_ns(), CAP_MAC_ADMIN)) > + return -EPERM; > + > + if (*ppos != 0) > + return -EINVAL; > + > + switch (file_entry->type) { > + case SAFESETID_WHITELIST_FLUSH: > + flush_safesetid_whitelist_entries(); > + break; > + case SAFESETID_WHITELIST_ADD: > + ret = parse_safesetid_whitelist_policy(buf, len, &parent, > + &child); > + if (ret) > + return ret; > + > + ret = add_safesetid_whitelist_entry(parent, child); > + if (ret) > + return ret; > + break; > + default: > + pr_warn("Unknown securityfs file %d\n", file_entry->type); > + break; > + } > + > + /* Return len on success so caller won't keep trying to write */ > + return len; > +} > + > +static const struct file_operations safesetid_file_fops = { > + .write = safesetid_file_write, > +}; > + > +static void safesetid_shutdown_securityfs(void) > +{ > + int i; > + > + for (i = 0; i < ARRAY_SIZE(safesetid_files); ++i) { > + struct safesetid_file_entry *entry = > + &safesetid_files[i]; > + securityfs_remove(entry->dentry); > + entry->dentry = NULL; > + } > + > + securityfs_remove(safesetid_policy_dir); > + safesetid_policy_dir = NULL; > +} > + > +static int __init safesetid_init_securityfs(void) > +{ > + int i; > + int ret; > + > + if (!safesetid_initialized) > + return 0; > + > + safesetid_policy_dir = securityfs_create_dir("safesetid", NULL); > + if (!safesetid_policy_dir) { > + ret = PTR_ERR(safesetid_policy_dir); > + goto error; > + } > + > + for (i = 0; i < ARRAY_SIZE(safesetid_files); ++i) { > + struct safesetid_file_entry *entry = > + &safesetid_files[i]; > + entry->dentry = securityfs_create_file( > + entry->name, 0200, safesetid_policy_dir, > + entry, &safesetid_file_fops); > + if (IS_ERR(entry->dentry)) { > + ret = PTR_ERR(entry->dentry); > + goto error; > + } > + } > + > + return 0; > + > +error: > + safesetid_shutdown_securityfs(); > + return ret; > +} > +fs_initcall(safesetid_init_securityfs);