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For debugging a running system, it is very helpful to be able to see what policy the system is using. Add a read handler that can dump out a copy of the loaded policy. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Micah Morton <mortonm@chromium.org>
225 lines
4.9 KiB
C
225 lines
4.9 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/security.h>
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#include <linux/cred.h>
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#include "lsm.h"
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static DEFINE_MUTEX(policy_update_lock);
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/*
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* In the case the input buffer contains one or more invalid UIDs, the kuid_t
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* variables pointed to by @parent and @child will get updated but this
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* function will return an error.
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* Contents of @buf may be modified.
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*/
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static int parse_policy_line(struct file *file, char *buf,
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struct setuid_rule *rule)
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{
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char *child_str;
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int ret;
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u32 parsed_parent, parsed_child;
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/* Format of |buf| string should be <UID>:<UID>. */
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child_str = strchr(buf, ':');
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if (child_str == NULL)
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return -EINVAL;
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*child_str = '\0';
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child_str++;
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ret = kstrtou32(buf, 0, &parsed_parent);
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if (ret)
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return ret;
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ret = kstrtou32(child_str, 0, &parsed_child);
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if (ret)
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return ret;
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rule->src_uid = make_kuid(file->f_cred->user_ns, parsed_parent);
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rule->dst_uid = make_kuid(file->f_cred->user_ns, parsed_child);
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if (!uid_valid(rule->src_uid) || !uid_valid(rule->dst_uid))
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return -EINVAL;
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return 0;
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}
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static void __release_ruleset(struct rcu_head *rcu)
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{
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struct setuid_ruleset *pol =
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container_of(rcu, struct setuid_ruleset, rcu);
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int bucket;
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struct setuid_rule *rule;
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struct hlist_node *tmp;
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hash_for_each_safe(pol->rules, bucket, tmp, rule, next)
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kfree(rule);
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kfree(pol->policy_str);
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kfree(pol);
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}
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static void release_ruleset(struct setuid_ruleset *pol)
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{
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call_rcu(&pol->rcu, __release_ruleset);
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}
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static ssize_t handle_policy_update(struct file *file,
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const char __user *ubuf, size_t len)
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{
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struct setuid_ruleset *pol;
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char *buf, *p, *end;
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int err;
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pol = kmalloc(sizeof(struct setuid_ruleset), GFP_KERNEL);
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if (!pol)
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return -ENOMEM;
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pol->policy_str = NULL;
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hash_init(pol->rules);
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p = buf = memdup_user_nul(ubuf, len);
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if (IS_ERR(buf)) {
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err = PTR_ERR(buf);
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goto out_free_pol;
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}
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pol->policy_str = kstrdup(buf, GFP_KERNEL);
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if (pol->policy_str == NULL) {
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err = -ENOMEM;
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goto out_free_buf;
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}
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/* policy lines, including the last one, end with \n */
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while (*p != '\0') {
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struct setuid_rule *rule;
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end = strchr(p, '\n');
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if (end == NULL) {
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err = -EINVAL;
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goto out_free_buf;
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}
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*end = '\0';
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rule = kmalloc(sizeof(struct setuid_rule), GFP_KERNEL);
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if (!rule) {
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err = -ENOMEM;
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goto out_free_buf;
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}
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err = parse_policy_line(file, p, rule);
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if (err)
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goto out_free_rule;
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if (_setuid_policy_lookup(pol, rule->src_uid, rule->dst_uid) ==
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SIDPOL_ALLOWED) {
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pr_warn("bad policy: duplicate entry\n");
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err = -EEXIST;
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goto out_free_rule;
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}
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hash_add(pol->rules, &rule->next, __kuid_val(rule->src_uid));
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p = end + 1;
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continue;
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out_free_rule:
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kfree(rule);
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goto out_free_buf;
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}
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/*
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* Everything looks good, apply the policy and release the old one.
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* What we really want here is an xchg() wrapper for RCU, but since that
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* doesn't currently exist, just use a spinlock for now.
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*/
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mutex_lock(&policy_update_lock);
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rcu_swap_protected(safesetid_setuid_rules, pol,
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lockdep_is_held(&policy_update_lock));
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mutex_unlock(&policy_update_lock);
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err = len;
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out_free_buf:
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kfree(buf);
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out_free_pol:
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release_ruleset(pol);
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return err;
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}
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static ssize_t safesetid_file_write(struct file *file,
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const char __user *buf,
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size_t len,
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loff_t *ppos)
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{
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if (!file_ns_capable(file, &init_user_ns, CAP_MAC_ADMIN))
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return -EPERM;
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if (*ppos != 0)
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return -EINVAL;
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return handle_policy_update(file, buf, len);
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}
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static ssize_t safesetid_file_read(struct file *file, char __user *buf,
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size_t len, loff_t *ppos)
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{
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ssize_t res = 0;
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struct setuid_ruleset *pol;
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const char *kbuf;
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mutex_lock(&policy_update_lock);
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pol = rcu_dereference_protected(safesetid_setuid_rules,
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lockdep_is_held(&policy_update_lock));
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if (pol) {
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kbuf = pol->policy_str;
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res = simple_read_from_buffer(buf, len, ppos,
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kbuf, strlen(kbuf));
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}
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mutex_unlock(&policy_update_lock);
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return res;
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}
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static const struct file_operations safesetid_file_fops = {
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.read = safesetid_file_read,
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.write = safesetid_file_write,
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};
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static int __init safesetid_init_securityfs(void)
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{
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int ret;
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struct dentry *policy_dir;
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struct dentry *policy_file;
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if (!safesetid_initialized)
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return 0;
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policy_dir = securityfs_create_dir("safesetid", NULL);
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if (IS_ERR(policy_dir)) {
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ret = PTR_ERR(policy_dir);
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goto error;
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}
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policy_file = securityfs_create_file("whitelist_policy", 0600,
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policy_dir, NULL, &safesetid_file_fops);
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if (IS_ERR(policy_file)) {
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ret = PTR_ERR(policy_file);
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goto error;
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}
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return 0;
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error:
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securityfs_remove(policy_dir);
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return ret;
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}
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fs_initcall(safesetid_init_securityfs);
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