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// OpenVPN -- An application to securely tunnel IP networks
// over a single port, with support for SSL/TLS-based
// session authentication and key exchange,
// packet encryption, packet authentication, and
// packet compression.
//
// Copyright (C) 2012-2022 OpenVPN Inc.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License Version 3
// as published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program in the COPYING file.
// If not, see <http://www.gnu.org/licenses/>.
// Drop root privileges but retain one or more Linux capabilities
#pragma once
#include <sys/capability.h>
#include <string>
#include <vector>
#include <utility>
#include <initializer_list>
#include <openvpn/common/numeric_cast.hpp>
#include <openvpn/common/usergroup.hpp>
#ifndef OPENVPN_PLATFORM_LINUX
#error SetUserGroupRetainCap requires Linux
#endif
namespace openvpn {
class SetUserGroupRetainCap : public SetUserGroup
{
public:
SetUserGroupRetainCap(const std::string &user,
const std::string &group,
const bool strict,
std::initializer_list<cap_value_t> retain_caps_arg)
: SetUserGroup(user, group, strict),
retain_caps(retain_caps_arg)
{
grab_root();
}
SetUserGroupRetainCap(const char *user,
const char *group,
const bool strict,
std::initializer_list<cap_value_t> retain_caps_arg)
: SetUserGroup(user, group, strict),
retain_caps(retain_caps_arg)
{
grab_root();
}
// call first in all threads before user/group downgrade
virtual void pre_thread() const override
{
if (!pw)
return;
// create a capabilities object
Capabilities cap("pre_thread");
// set retained capabilities + setuid/setgid
cap.set_flag_with_setuid_setgid(retain_caps);
// commit it to kernel
cap.set_proc();
// retain the capabilities across identity change
if (::prctl(PR_SET_KEEPCAPS, 1L))
{
const int eno = errno;
OPENVPN_THROW(user_group_err, "SetUserGroupRetainCap prctl PR_SET_KEEPCAPS fail: " << strerror_str(eno));
}
}
// call once after pre_thread() called in each thread
virtual void activate() const override
{
if (!pw)
{
SetUserGroup::activate();
return;
}
// set GID/Groups
do_setgid_setgroups();
// drop extra privileges (aside from capabilities)
if (::setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid))
{
const int eno = errno;
OPENVPN_THROW(user_group_err, "SetUserGroupRetainCap setresuid user fail: " << strerror_str(eno));
}
// retain core dumps after UID/GID downgrade
retain_core_dumps();
// logging
{
Capabilities cap("logging");
cap.set_flag(retain_caps);
OPENVPN_LOG("UID [" << cap.to_string() << "] set to '" << user_name << '\'');
}
}
// call in all threads after activate()
virtual void post_thread() const override
{
if (!pw)
return;
// create a capabilities object
Capabilities cap("post_thread");
// set retained capabilities
cap.set_flag(retain_caps);
// commit it to kernel
cap.set_proc();
}
private:
class Capabilities
{
public:
Capabilities(std::string title_arg)
: capabilities(::cap_init()),
title(std::move(title_arg))
{
}
~Capabilities()
{
::cap_free(capabilities);
}
void set_flag(const std::vector<cap_value_t> &caps)
{
if (::cap_set_flag(capabilities, CAP_PERMITTED, numeric_cast<int>(caps.size()), caps.data(), CAP_SET)
|| ::cap_set_flag(capabilities, CAP_EFFECTIVE, numeric_cast<int>(caps.size()), caps.data(), CAP_SET))
{
const int eno = errno;
OPENVPN_THROW(user_group_err, "SetUserGroupRetainCap::Capabilities: cap_set_flag " << title << " fail: " << strerror_str(eno));
}
}
void set_flag_with_setuid_setgid(std::vector<cap_value_t> caps)
{
caps.push_back(CAP_SETUID);
caps.push_back(CAP_SETGID);
set_flag(caps);
}
void set_proc()
{
if (::cap_set_proc(capabilities))
{
const int eno = errno;
OPENVPN_THROW(user_group_err, "SetUserGroupRetainCap::Capabilities: cap_set_proc " << title << " fail: " << strerror_str(eno));
}
}
std::string to_string() const
{
char *txt = ::cap_to_text(capabilities, nullptr);
std::string ret(txt);
::cap_free(txt);
return ret;
}
private:
Capabilities(const Capabilities &) = delete;
Capabilities &operator=(const Capabilities &) = delete;
const cap_t capabilities;
const std::string title;
};
void grab_root()
{
// get full root privileges
if (::setresuid(0, 0, 0))
{
const int eno = errno;
OPENVPN_THROW(user_group_err, "SetUserGroupRetainCap setresuid root fail: " << strerror_str(eno));
}
}
const std::vector<cap_value_t> retain_caps;
};
} // namespace openvpn
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