process.hpp

//    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/>.

// General-purpose classes for instantiating a posix process with arguments.

#pragma once
#ifndef _WIN32

#include <stdlib.h>    // exit
#include <unistd.h>    // fork, execve
#include <sys/types.h> // waitpid
#include <sys/wait.h>  // waitpid

#include <string>
#include <memory>
#include <utility>

#include <openvpn/common/action.hpp>
#include <openvpn/common/redir.hpp>
#include <openvpn/common/signal.hpp>
#include <openvpn/common/argv.hpp>
#include <openvpn/common/environ.hpp>

namespace openvpn {

// low-level fork/exec (async)
inline pid_t system_cmd_async(const std::string &cmd,
                              const Argv &argv,
                              const Environ *env,
                              RedirectBase *redir,
                              const sigset_t *sigmask)
{
    ArgvWrapper argv_wrap(argv);
    std::unique_ptr<ArgvWrapper> env_wrap;
    if (env)
        env_wrap.reset(new ArgvWrapper(*env));
    auto fn = cmd.c_str();
    auto av = argv_wrap.c_argv();
    auto ev = env_wrap ? env_wrap->c_argv() : ::environ;

#if defined(__APPLE__)
    /* macOS vfork is deprecated and behaves identical to fork() */
    const pid_t pid = ::fork();
#else
    const pid_t pid = (redir || sigmask) ? ::fork() : ::vfork();
#endif

    if (pid == pid_t(0)) /* child side */
    {
        // Only Async-signal-safe functions as specified by
        // SIGNAL(7) can be called between here and _exit().
        if (sigmask)
            ::pthread_sigmask(SIG_SETMASK, sigmask, 0);
        if (redir)
            redir->redirect();
        ::execve(fn, av, ev);
        ::_exit(127);
    }
    else if (pid < pid_t(0)) /* fork failed */
        return -1;
    else /* parent side */
    {
        if (redir)
            redir->close();
        return pid;
    }
}

// completion for system_cmd_async()
inline int system_cmd_post(const pid_t pid)
{
    int status = -1;
    if (::waitpid(pid, &status, 0) == pid)
    {
        if (WIFEXITED(status))
            return WEXITSTATUS(status);
    }
    return -1;
}

// synchronous version of system_cmd_async
inline int system_cmd(const std::string &cmd,
                      const Argv &argv,
                      RedirectBase *redir,
                      const Environ *env,
                      const sigset_t *sigmask)
{
    const pid_t pid = system_cmd_async(cmd, argv, env, redir, sigmask);
    if (pid < pid_t(0))
        return -1;
    return system_cmd_post(pid);
}

// simple command execution
inline int system_cmd(const std::string &cmd, const Argv &argv)
{
    return system_cmd(cmd, argv, nullptr, nullptr, nullptr);
}

// simple command execution
inline int system_cmd(const Argv &argv)
{
    int ret = -1;
    if (argv.size())
        ret = system_cmd(argv[0], argv);
    return ret;
}

// command execution with std::strings as
// input/output/error (uses pipes under the
// hood)
inline int system_cmd(const std::string &cmd,
                      const Argv &argv,
                      const Environ *env,
                      RedirectPipe::InOut &inout,
                      unsigned int redirect_pipe_flags,
                      const sigset_t *sigmask)
{
    SignalBlockerPipe sbpipe;
    RedirectPipe remote;
    if (!inout.in.empty())
        redirect_pipe_flags |= RedirectPipe::ENABLE_IN;
    RedirectPipe local(remote, redirect_pipe_flags);
    const pid_t pid = system_cmd_async(cmd, argv, env, &remote, sigmask);
    if (pid < pid_t(0))
        return -1;
    local.transact(inout);
    return system_cmd_post(pid);
}

struct Command : public Action
{
    typedef RCPtr<Command> Ptr;

    Command()
    {
    }

    Command(Argv argv_arg)
        : argv(std::move(argv_arg))
    {
    }

    Command *copy() const
    {
        Command *ret = new Command;
        ret->argv = argv;
        return ret;
    }

    virtual void execute(std::ostream &os) override
    {
        if (!argv.empty())
        {
            os << to_string() << std::endl;
#ifdef OPENVPN_PROCESS_AVOID_PIPES
            const int status = system_cmd(argv[0], argv);
            if (status < 0)
                os << "Error: command failed to execute" << std::endl;
#else
            RedirectPipe::InOut inout;
            const int status = system_cmd(argv[0], argv, nullptr, inout, RedirectPipe::COMBINE_OUT_ERR, nullptr);
            if (status < 0)
                os << "Error: command failed to execute" << std::endl;
            os << inout.out;
#endif
        }
        else
            os << "Error: command called with empty argv" << std::endl;
    }

    virtual std::string to_string() const override
    {
        return argv.to_string();
    }

    Argv argv;
};

} // namespace openvpn

#endif