/*

* 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;

   }

}