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/*
* Gather entropy by running various system commands in the hopes that
* some of the output cannot be guessed by a remote attacker.
*
* (C) 1999-2009,2013 Jack Lloyd
* 2012 Markus Wanner
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/unix_procs.h>
#include <botan/parsing.h>
#include <algorithm>
#include <atomic>
#include <sys/time.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/resource.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
namespace Botan {
namespace {
std::string find_full_path_if_exists(const std::vector<std::string>& trusted_path,
const std::string& proc)
{
for(auto dir : trusted_path)
{
const std::string full_path = dir + "/" + proc;
if(::access(full_path.c_str(), X_OK) == 0)
return full_path;
}
return "";
}
size_t concurrent_processes(size_t user_request)
{
const size_t DEFAULT_CONCURRENT = 2;
const size_t MAX_CONCURRENT = 8;
if(user_request > 0)
return std::min(user_request, MAX_CONCURRENT);
const long online_cpus = ::sysconf(_SC_NPROCESSORS_ONLN);
if(online_cpus > 0)
return static_cast<size_t>(online_cpus); // maybe fewer?
return DEFAULT_CONCURRENT;
}
}
/**
* Unix_EntropySource Constructor
*/
Unix_EntropySource::Unix_EntropySource(const std::vector<std::string>& trusted_path,
size_t proc_cnt) :
m_trusted_paths(trusted_path),
m_concurrent(concurrent_processes(proc_cnt))
{
}
void UnixProcessInfo_EntropySource::poll(Entropy_Accumulator& accum)
{
accum.add(::getpid(), BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
accum.add(::getppid(), BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
accum.add(::getuid(), BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
accum.add(::getgid(), BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
accum.add(::getpgrp(), BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
struct ::rusage usage;
::getrusage(RUSAGE_SELF, &usage);
accum.add(usage, BOTAN_ENTROPY_ESTIMATE_STATIC_SYSTEM_DATA);
}
void Unix_EntropySource::Unix_Process::spawn(const std::vector<std::string>& args)
{
if(args.empty())
throw Invalid_Argument("Cannot spawn process without path");
shutdown();
int pipe[2];
if(::pipe(pipe) != 0)
return;
pid_t pid = ::fork();
if(pid == -1)
{
::close(pipe[0]);
::close(pipe[1]);
}
else if(pid > 0) // in parent
{
m_pid = pid;
m_fd = pipe[0];
::close(pipe[1]);
}
else // in child
{
if(::dup2(pipe[1], STDOUT_FILENO) == -1)
::exit(127);
if(::close(pipe[0]) != 0 || ::close(pipe[1]) != 0)
::exit(127);
if(close(STDERR_FILENO) != 0)
::exit(127);
const char* arg0 = args[0].c_str();
const char* arg1 = (args.size() > 1) ? args[1].c_str() : nullptr;
const char* arg2 = (args.size() > 2) ? args[2].c_str() : nullptr;
const char* arg3 = (args.size() > 3) ? args[3].c_str() : nullptr;
const char* arg4 = (args.size() > 4) ? args[4].c_str() : nullptr;
::execl(arg0, arg0, arg1, arg2, arg3, arg4, NULL);
::exit(127);
}
}
void Unix_EntropySource::Unix_Process::shutdown()
{
if(m_pid == -1)
return;
::close(m_fd);
m_fd = -1;
pid_t reaped = waitpid(m_pid, nullptr, WNOHANG);
if(reaped == 0)
{
/*
* Child is still alive - send it SIGTERM, sleep for a bit and
* try to reap again, if still alive send SIGKILL
*/
kill(m_pid, SIGTERM);
struct ::timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 1000;
select(0, nullptr, nullptr, nullptr, &tv);
reaped = ::waitpid(m_pid, nullptr, WNOHANG);
if(reaped == 0)
{
::kill(m_pid, SIGKILL);
do
reaped = ::waitpid(m_pid, nullptr, 0);
while(reaped == -1);
}
}
m_pid = -1;
}
const std::vector<std::string>& Unix_EntropySource::next_source()
{
const auto& src = m_sources.at(m_sources_idx);
m_sources_idx = (m_sources_idx + 1) % m_sources.size();
return src;
}
void Unix_EntropySource::poll(Entropy_Accumulator& accum)
{
// refuse to run setuid or setgid, or as root
if((getuid() != geteuid()) || (getgid() != getegid()) || (geteuid() == 0))
return;
std::lock_guard<std::mutex> lock(m_mutex);
if(m_sources.empty())
{
auto sources = get_default_sources();
for(auto src : sources)
{
const std::string path = find_full_path_if_exists(m_trusted_paths, src[0]);
if(path != "")
{
src[0] = path;
m_sources.push_back(src);
}
}
}
if(m_sources.empty())
return; // still empty, really nothing to try
const size_t MS_WAIT_TIME = 32;
m_buf.resize(4096);
while(!accum.polling_finished())
{
while(m_procs.size() < m_concurrent)
m_procs.emplace_back(Unix_Process(next_source()));
fd_set read_set;
FD_ZERO(&read_set);
std::vector<int> fds;
for(auto& proc : m_procs)
{
int fd = proc.fd();
if(fd > 0)
{
fds.push_back(fd);
FD_SET(fd, &read_set);
}
}
if(fds.empty())
break;
const int max_fd = *std::max_element(fds.begin(), fds.end());
struct ::timeval timeout;
timeout.tv_sec = (MS_WAIT_TIME / 1000);
timeout.tv_usec = (MS_WAIT_TIME % 1000) * 1000;
if(::select(max_fd + 1, &read_set, nullptr, nullptr, &timeout) < 0)
return; // or continue?
for(auto& proc : m_procs)
{
int fd = proc.fd();
if(FD_ISSET(fd, &read_set))
{
const ssize_t got = ::read(fd, m_buf.data(), m_buf.size());
if(got > 0)
accum.add(m_buf.data(), got, BOTAN_ENTROPY_ESTIMATE_SYSTEM_TEXT);
else
proc.spawn(next_source());
}
}
}
}
}
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