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/*
* Entropy source based on reading files in /proc on the assumption
* that a remote attacker will have difficulty guessing some of them.
*
* (C) 1999-2008,2012 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/proc_walk.h>
#include <deque>
#ifndef _POSIX_C_SOURCE
#define _POSIX_C_SOURCE 199309
#endif
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <dirent.h>
#include <fcntl.h>
namespace Botan {
namespace {
class Directory_Walker final : public File_Descriptor_Source
{
public:
explicit Directory_Walker(const std::string& root) :
m_cur_dir(std::make_pair<DIR*, std::string>(nullptr, ""))
{
if(DIR* root_dir = ::opendir(root.c_str()))
m_cur_dir = std::make_pair(root_dir, root);
}
~Directory_Walker()
{
if(m_cur_dir.first)
::closedir(m_cur_dir.first);
}
int next_fd() override;
private:
std::pair<struct dirent*, std::string> get_next_dirent();
std::pair<DIR*, std::string> m_cur_dir;
std::deque<std::string> m_dirlist;
};
std::pair<struct dirent*, std::string> Directory_Walker::get_next_dirent()
{
while(m_cur_dir.first)
{
if(struct dirent* dir = ::readdir(m_cur_dir.first))
return std::make_pair(dir, m_cur_dir.second);
::closedir(m_cur_dir.first);
m_cur_dir = std::make_pair<DIR*, std::string>(nullptr, "");
while(!m_dirlist.empty() && !m_cur_dir.first)
{
const std::string next_dir_name = m_dirlist[0];
m_dirlist.pop_front();
if(DIR* next_dir = ::opendir(next_dir_name.c_str()))
m_cur_dir = std::make_pair(next_dir, next_dir_name);
}
}
return std::make_pair<struct dirent*, std::string>(nullptr, ""); // nothing left
}
int Directory_Walker::next_fd()
{
while(true)
{
std::pair<struct dirent*, std::string> entry = get_next_dirent();
if(!entry.first)
break; // no more dirs
const std::string filename = entry.first->d_name;
if(filename == "." || filename == "..")
continue;
const std::string full_path = entry.second + "/" + filename;
struct stat stat_buf;
if(::lstat(full_path.c_str(), &stat_buf) == -1)
continue;
if(S_ISDIR(stat_buf.st_mode))
{
m_dirlist.push_back(full_path);
}
else if(S_ISREG(stat_buf.st_mode) && (stat_buf.st_mode & S_IROTH))
{
int fd = ::open(full_path.c_str(), O_RDONLY | O_NOCTTY);
if(fd >= 0)
return fd;
}
}
return -1;
}
}
size_t ProcWalking_EntropySource::poll(RandomNumberGenerator& rng)
{
const size_t MAX_FILES_READ_PER_POLL = 2048;
lock_guard_type<mutex_type> lock(m_mutex);
if(!m_dir)
m_dir.reset(new Directory_Walker(m_path));
m_buf.resize(4096);
size_t bits = 0;
for(size_t i = 0; i != MAX_FILES_READ_PER_POLL; ++i)
{
int fd = m_dir->next_fd();
// If we've exhaused this walk of the directory, halt the poll
if(fd == -1)
{
m_dir.reset();
break;
}
ssize_t got = ::read(fd, m_buf.data(), m_buf.size());
::close(fd);
if(got > 0)
{
rng.add_entropy(m_buf.data(), static_cast<size_t>(got));
// Conservative estimate of 4 bits per file
bits += 4;
}
if(bits > 128)
break;
}
return bits;
}
}