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// SPDX-License-Identifier: GPL-2.0
/*
* SafeSetID Linux Security Module
*
* Author: Micah Morton <mortonm@chromium.org>
*
* 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 <linux/security.h>
#include <linux/cred.h>
#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.
* Contents of @buf may be modified.
*/
static int parse_policy_line(
struct file *file, char *buf, kuid_t *parent, kuid_t *child)
{
char *child_str;
int ret;
u32 parsed_parent, parsed_child;
/* Format of |buf| string should be <UID>:<UID>. */
child_str = strchr(buf, ':');
if (child_str == NULL)
return -EINVAL;
*child_str = '\0';
child_str++;
ret = kstrtou32(buf, 0, &parsed_parent);
if (ret)
return ret;
ret = kstrtou32(child_str, 0, &parsed_child);
if (ret)
return ret;
*parent = make_kuid(file->f_cred->user_ns, parsed_parent);
*child = make_kuid(file->f_cred->user_ns, parsed_child);
if (!uid_valid(*parent) || !uid_valid(*child))
return -EINVAL;
return 0;
}
static int parse_safesetid_whitelist_policy(
struct file *file, const char __user *buf, size_t len,
kuid_t *parent, kuid_t *child)
{
char *kern_buf = memdup_user_nul(buf, len);
int ret;
if (IS_ERR(kern_buf))
return PTR_ERR(kern_buf);
ret = parse_policy_line(file, kern_buf, parent, child);
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 (!file_ns_capable(file, &init_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(file, 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 (IS_ERR(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);
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