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![Jann Horn](/assets/img/avatar_default.png)
Fix the pr_warn() calls in the SafeSetID LSM to have newlines at the end. Without this, denial messages will be buffered as incomplete lines in log_output(), and will then only show up once something else prints into dmesg. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Micah Morton <mortonm@chromium.org>
277 lines
7.7 KiB
C
277 lines
7.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* SafeSetID Linux Security Module
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*
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* Author: Micah Morton <mortonm@chromium.org>
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*
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* Copyright (C) 2018 The Chromium OS Authors.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2, as
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* published by the Free Software Foundation.
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*
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*/
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#define pr_fmt(fmt) "SafeSetID: " fmt
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#include <linux/hashtable.h>
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#include <linux/lsm_hooks.h>
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#include <linux/module.h>
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#include <linux/ptrace.h>
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#include <linux/sched/task_stack.h>
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#include <linux/security.h>
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/* Flag indicating whether initialization completed */
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int safesetid_initialized;
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#define NUM_BITS 8 /* 128 buckets in hash table */
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static DEFINE_HASHTABLE(safesetid_whitelist_hashtable, NUM_BITS);
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/*
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* Hash table entry to store safesetid policy signifying that 'parent' user
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* can setid to 'child' user.
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*/
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struct entry {
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struct hlist_node next;
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struct hlist_node dlist; /* for deletion cleanup */
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uint64_t parent_kuid;
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uint64_t child_kuid;
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};
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static DEFINE_SPINLOCK(safesetid_whitelist_hashtable_spinlock);
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static bool check_setuid_policy_hashtable_key(kuid_t parent)
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{
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struct entry *entry;
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rcu_read_lock();
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hash_for_each_possible_rcu(safesetid_whitelist_hashtable,
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entry, next, __kuid_val(parent)) {
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if (entry->parent_kuid == __kuid_val(parent)) {
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rcu_read_unlock();
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return true;
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}
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}
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rcu_read_unlock();
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return false;
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}
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static bool check_setuid_policy_hashtable_key_value(kuid_t parent,
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kuid_t child)
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{
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struct entry *entry;
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rcu_read_lock();
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hash_for_each_possible_rcu(safesetid_whitelist_hashtable,
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entry, next, __kuid_val(parent)) {
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if (entry->parent_kuid == __kuid_val(parent) &&
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entry->child_kuid == __kuid_val(child)) {
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rcu_read_unlock();
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return true;
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}
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}
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rcu_read_unlock();
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return false;
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}
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static int safesetid_security_capable(const struct cred *cred,
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struct user_namespace *ns,
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int cap,
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unsigned int opts)
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{
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if (cap == CAP_SETUID &&
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check_setuid_policy_hashtable_key(cred->uid)) {
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if (!(opts & CAP_OPT_INSETID)) {
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/*
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* Deny if we're not in a set*uid() syscall to avoid
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* giving powers gated by CAP_SETUID that are related
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* to functionality other than calling set*uid() (e.g.
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* allowing user to set up userns uid mappings).
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*/
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pr_warn("Operation requires CAP_SETUID, which is not available to UID %u for operations besides approved set*uid transitions\n",
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__kuid_val(cred->uid));
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return -1;
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}
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}
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return 0;
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}
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static int check_uid_transition(kuid_t parent, kuid_t child)
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{
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if (check_setuid_policy_hashtable_key_value(parent, child))
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return 0;
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pr_warn("UID transition (%d -> %d) blocked\n",
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__kuid_val(parent),
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__kuid_val(child));
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/*
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* Kill this process to avoid potential security vulnerabilities
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* that could arise from a missing whitelist entry preventing a
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* privileged process from dropping to a lesser-privileged one.
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*/
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force_sig(SIGKILL);
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return -EACCES;
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}
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/*
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* Check whether there is either an exception for user under old cred struct to
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* set*uid to user under new cred struct, or the UID transition is allowed (by
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* Linux set*uid rules) even without CAP_SETUID.
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*/
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static int safesetid_task_fix_setuid(struct cred *new,
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const struct cred *old,
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int flags)
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{
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/* Do nothing if there are no setuid restrictions for this UID. */
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if (!check_setuid_policy_hashtable_key(old->uid))
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return 0;
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switch (flags) {
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case LSM_SETID_RE:
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/*
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* Users for which setuid restrictions exist can only set the
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* real UID to the real UID or the effective UID, unless an
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* explicit whitelist policy allows the transition.
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*/
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if (!uid_eq(old->uid, new->uid) &&
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!uid_eq(old->euid, new->uid)) {
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return check_uid_transition(old->uid, new->uid);
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}
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/*
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* Users for which setuid restrictions exist can only set the
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* effective UID to the real UID, the effective UID, or the
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* saved set-UID, unless an explicit whitelist policy allows
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* the transition.
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*/
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if (!uid_eq(old->uid, new->euid) &&
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!uid_eq(old->euid, new->euid) &&
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!uid_eq(old->suid, new->euid)) {
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return check_uid_transition(old->euid, new->euid);
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}
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break;
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case LSM_SETID_ID:
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/*
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* Users for which setuid restrictions exist cannot change the
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* real UID or saved set-UID unless an explicit whitelist
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* policy allows the transition.
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*/
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if (!uid_eq(old->uid, new->uid))
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return check_uid_transition(old->uid, new->uid);
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if (!uid_eq(old->suid, new->suid))
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return check_uid_transition(old->suid, new->suid);
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break;
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case LSM_SETID_RES:
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/*
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* Users for which setuid restrictions exist cannot change the
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* real UID, effective UID, or saved set-UID to anything but
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* one of: the current real UID, the current effective UID or
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* the current saved set-user-ID unless an explicit whitelist
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* policy allows the transition.
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*/
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if (!uid_eq(new->uid, old->uid) &&
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!uid_eq(new->uid, old->euid) &&
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!uid_eq(new->uid, old->suid)) {
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return check_uid_transition(old->uid, new->uid);
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}
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if (!uid_eq(new->euid, old->uid) &&
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!uid_eq(new->euid, old->euid) &&
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!uid_eq(new->euid, old->suid)) {
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return check_uid_transition(old->euid, new->euid);
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}
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if (!uid_eq(new->suid, old->uid) &&
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!uid_eq(new->suid, old->euid) &&
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!uid_eq(new->suid, old->suid)) {
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return check_uid_transition(old->suid, new->suid);
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}
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break;
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case LSM_SETID_FS:
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/*
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* Users for which setuid restrictions exist cannot change the
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* filesystem UID to anything but one of: the current real UID,
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* the current effective UID or the current saved set-UID
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* unless an explicit whitelist policy allows the transition.
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*/
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if (!uid_eq(new->fsuid, old->uid) &&
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!uid_eq(new->fsuid, old->euid) &&
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!uid_eq(new->fsuid, old->suid) &&
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!uid_eq(new->fsuid, old->fsuid)) {
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return check_uid_transition(old->fsuid, new->fsuid);
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}
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break;
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default:
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pr_warn("Unknown setid state %d\n", flags);
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force_sig(SIGKILL);
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return -EINVAL;
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}
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return 0;
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}
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int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child)
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{
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struct entry *new;
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/* Return if entry already exists */
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if (check_setuid_policy_hashtable_key_value(parent, child))
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return 0;
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new = kzalloc(sizeof(struct entry), GFP_KERNEL);
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if (!new)
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return -ENOMEM;
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new->parent_kuid = __kuid_val(parent);
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new->child_kuid = __kuid_val(child);
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spin_lock(&safesetid_whitelist_hashtable_spinlock);
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hash_add_rcu(safesetid_whitelist_hashtable,
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&new->next,
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__kuid_val(parent));
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spin_unlock(&safesetid_whitelist_hashtable_spinlock);
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return 0;
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}
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void flush_safesetid_whitelist_entries(void)
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{
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struct entry *entry;
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struct hlist_node *hlist_node;
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unsigned int bkt_loop_cursor;
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HLIST_HEAD(free_list);
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/*
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* Could probably use hash_for_each_rcu here instead, but this should
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* be fine as well.
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*/
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spin_lock(&safesetid_whitelist_hashtable_spinlock);
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hash_for_each_safe(safesetid_whitelist_hashtable, bkt_loop_cursor,
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hlist_node, entry, next) {
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hash_del_rcu(&entry->next);
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hlist_add_head(&entry->dlist, &free_list);
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}
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spin_unlock(&safesetid_whitelist_hashtable_spinlock);
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synchronize_rcu();
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hlist_for_each_entry_safe(entry, hlist_node, &free_list, dlist) {
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hlist_del(&entry->dlist);
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kfree(entry);
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}
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}
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static struct security_hook_list safesetid_security_hooks[] = {
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LSM_HOOK_INIT(task_fix_setuid, safesetid_task_fix_setuid),
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LSM_HOOK_INIT(capable, safesetid_security_capable)
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};
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static int __init safesetid_security_init(void)
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{
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security_add_hooks(safesetid_security_hooks,
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ARRAY_SIZE(safesetid_security_hooks), "safesetid");
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/* Report that SafeSetID successfully initialized */
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safesetid_initialized = 1;
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return 0;
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}
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DEFINE_LSM(safesetid_security_init) = {
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.init = safesetid_security_init,
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.name = "safesetid",
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};
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