Do not create file when RPC user/pass is given and use file locking

src/common/util.cpp

@@ -43,7 +43,9 @@ using namespace epee;
   #include <shlobj.h>
   #include <strsafe.h>
 #else 
+  #include <sys/file.h>
   #include <sys/utsname.h>
+  #include <sys/stat.h>
 #endif
 #include <boost/filesystem.hpp>
 #include <boost/asio.hpp>
@@ -53,7 +55,12 @@ namespace tools
 {
   std::function<void(int)> signal_handler::m_handler;
 
-  std::unique_ptr<std::FILE, tools::close_file> create_private_file(const std::string& name)
+  private_file::private_file() noexcept : m_handle(), m_filename() {}
+
+  private_file::private_file(std::FILE* handle, std::string&& filename) noexcept
+    : m_handle(handle), m_filename(std::move(filename)) {}
+
+  private_file private_file::create(std::string name)
   {
 #ifdef WIN32
     struct close_handle
@@ -70,17 +77,17 @@ namespace tools
       const bool fail = OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, std::addressof(temp)) == 0;
       process.reset(temp);
       if (fail)
-        return nullptr;
+        return {};
     }
 
     DWORD sid_size = 0;
     GetTokenInformation(process.get(), TokenOwner, nullptr, 0, std::addressof(sid_size));
     if (GetLastError() != ERROR_INSUFFICIENT_BUFFER)
-      return nullptr;
+      return {};
 
     std::unique_ptr<char[]> sid{new char[sid_size]};
     if (!GetTokenInformation(process.get(), TokenOwner, sid.get(), sid_size, std::addressof(sid_size)))
-      return nullptr;
+      return {};
 
     const PSID psid = reinterpret_cast<const PTOKEN_OWNER>(sid.get())->Owner;
     const DWORD daclSize =
@@ -88,17 +95,17 @@ namespace tools
 
     const std::unique_ptr<char[]> dacl{new char[daclSize]};
     if (!InitializeAcl(reinterpret_cast<PACL>(dacl.get()), daclSize, ACL_REVISION))
-      return nullptr;
+      return {};
 
     if (!AddAccessAllowedAce(reinterpret_cast<PACL>(dacl.get()), ACL_REVISION, (READ_CONTROL | FILE_GENERIC_READ | DELETE), psid))
-      return nullptr;
+      return {};
 
     SECURITY_DESCRIPTOR descriptor{};
     if (!InitializeSecurityDescriptor(std::addressof(descriptor), SECURITY_DESCRIPTOR_REVISION))
-      return nullptr;
+      return {};
 
     if (!SetSecurityDescriptorDacl(std::addressof(descriptor), true, reinterpret_cast<PACL>(dacl.get()), false))
-      return nullptr;
+      return {};
 
     SECURITY_ATTRIBUTES attributes{sizeof(SECURITY_ATTRIBUTES), std::addressof(descriptor), false};
     std::unique_ptr<void, close_handle> file{
@@ -106,7 +113,7 @@ namespace tools
         name.c_str(),
         GENERIC_WRITE, FILE_SHARE_READ,
         std::addressof(attributes),
-        CREATE_NEW, FILE_ATTRIBUTE_TEMPORARY,
+        CREATE_NEW, (FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE),
         nullptr
       )
     };
@@ -121,22 +128,49 @@ namespace tools
         {
           _close(fd);
         }
-        return {real_file, tools::close_file{}};
+        return {real_file, std::move(name)};
       }
     }
 #else
-    const int fd = open(name.c_str(), (O_RDWR | O_EXCL | O_CREAT), S_IRUSR);
+    const int fdr = open(name.c_str(), (O_RDONLY | O_CREAT), S_IRUSR);
-    if (0 <= fd)
+    if (0 <= fdr)
     {
-      std::FILE* file = fdopen(fd, "w");
+      struct stat rstats = {};
-      if (!file)
+      if (fstat(fdr, std::addressof(rstats)) != 0)
       {
-        close(fd);
+        close(fdr);
+        return {};
+      }
+      fchmod(fdr, (S_IRUSR | S_IWUSR));
+      const int fdw = open(name.c_str(), O_RDWR);
+      fchmod(fdr, rstats.st_mode);
+      close(fdr);
+
+      if (0 <= fdw)
+      {
+        struct stat wstats = {};
+        if (fstat(fdw, std::addressof(wstats)) == 0 &&
+            rstats.st_dev == wstats.st_dev && rstats.st_ino == wstats.st_ino &&
+            flock(fdw, (LOCK_EX | LOCK_NB)) == 0 && ftruncate(fdw, 0) == 0)
+        {
+          std::FILE* file = fdopen(fdw, "w");
+          if (file) return {file, std::move(name)};
+        }
+        close(fdw);
       }
-      return {file, tools::close_file{}};
     }
 #endif
-    return nullptr;
+    return {};
+  }
+
+  private_file::~private_file() noexcept
+  {
+    try
+    {
+      boost::system::error_code ec{};
+      boost::filesystem::remove(filename(), ec);
+    }
+    catch (...) {}
   }
 
 #ifdef WIN32

src/common/util.h

@@ -60,8 +60,30 @@ namespace tools
     }
   };
 
-  //! \return File only readable by owner. nullptr if `filename` exists.
+  //! A file restricted to process owner AND process. Deletes file on destruction.
-  std::unique_ptr<std::FILE, close_file> create_private_file(const std::string& filename);
+  class private_file {
+    std::unique_ptr<std::FILE, close_file> m_handle;
+    std::string m_filename;
+
+    private_file(std::FILE* handle, std::string&& filename) noexcept;
+  public:
+
+    //! `handle() == nullptr && filename.empty()`.
+    private_file() noexcept;
+
+    /*! \return File only readable by owner and only used by this process
+      OR `private_file{}` on error. */
+    static private_file create(std::string filename);
+
+    private_file(private_file&&) = default;
+    private_file& operator=(private_file&&) = default;
+
+    //! Deletes `filename()` and closes `handle()`.
+    ~private_file() noexcept;
+
+    std::FILE* handle() const noexcept { return m_handle.get(); }
+    const std::string& filename() const noexcept { return m_filename; }
+  };
 
   /*! \brief Returns the default data directory.
    *

src/wallet/wallet_rpc_server.cpp

@@ -37,7 +37,6 @@ using namespace epee;
 #include "wallet/wallet_args.h"
 #include "common/command_line.h"
 #include "common/i18n.h"
-#include "common/util.h"
 #include "cryptonote_basic/cryptonote_format_utils.h"
 #include "cryptonote_basic/account.h"
 #include "wallet_rpc_server_commands_defs.h"
@@ -70,18 +69,12 @@ namespace tools
   }
 
   //------------------------------------------------------------------------------------------------------------------------------
-  wallet_rpc_server::wallet_rpc_server():m_wallet(NULL), rpc_login_filename(), m_stop(false), m_trusted_daemon(false)
+  wallet_rpc_server::wallet_rpc_server():m_wallet(NULL), rpc_login_file(), m_stop(false), m_trusted_daemon(false)
   {
   }
   //------------------------------------------------------------------------------------------------------------------------------
   wallet_rpc_server::~wallet_rpc_server()
   {
-    try
-    {
-      boost::system::error_code ec{};
-      boost::filesystem::remove(rpc_login_filename, ec);
-    }
-    catch (...) {}
   }
   //------------------------------------------------------------------------------------------------------------------------------
   void wallet_rpc_server::set_wallet(wallet2 *cr)
@@ -182,34 +175,32 @@ namespace tools
           default_rpc_username,
           string_encoding::base64_encode(rand_128bit.data(), rand_128bit.size())
         );
+
+        std::string temp = "monero-wallet-rpc." + bind_port + ".login";
+        rpc_login_file = tools::private_file::create(temp);
+        if (!rpc_login_file.handle())
+        {
+          LOG_ERROR(tr("Failed to create file ") << temp << tr(". Check permissions or remove file"));
+          return false;
         }
-      else
+        std::fputs(http_login->username.c_str(), rpc_login_file.handle());
+        std::fputc(':', rpc_login_file.handle());
+        std::fputs(http_login->password.c_str(), rpc_login_file.handle());
+        std::fflush(rpc_login_file.handle());
+        if (std::ferror(rpc_login_file.handle()))
+        {
+          LOG_ERROR(tr("Error writing to file ") << temp);
+          return false;
+        }
+        LOG_PRINT_L0(tr("RPC username/password is stored in file ") << temp);
+      }
+      else // chosen user/pass
       {
         http_login.emplace(
           std::move(rpc_config->login->username), std::move(rpc_config->login->password).password()
         );
       }
       assert(bool(http_login));
-
-      std::string temp = "monero-wallet-rpc." + bind_port + ".login";
-      const auto cookie = tools::create_private_file(temp);
-      if (!cookie)
-      {
-        LOG_ERROR(tr("Failed to create file ") << temp << tr(". Check permissions or remove file"));
-        return false;
-      }
-      rpc_login_filename.swap(temp); // nothrow guarantee destructor cleanup
-      temp = rpc_login_filename;
-      std::fputs(http_login->username.c_str(), cookie.get());
-      std::fputc(':', cookie.get());
-      std::fputs(http_login->password.c_str(), cookie.get());
-      std::fflush(cookie.get());
-      if (std::ferror(cookie.get()))
-      {
-        LOG_ERROR(tr("Error writing to file ") << temp);
-        return false;
-      }
-      LOG_PRINT_L0(tr("RPC username/password is stored in file ") << temp);
     } // end auth enabled
 
     m_http_client.set_server(walvars->get_daemon_address(), walvars->get_daemon_login());

src/wallet/wallet_rpc_server.h

@@ -33,6 +33,7 @@
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/variables_map.hpp>
 #include <string>
+#include "common/util.h"
 #include "net/http_server_impl_base.h"
 #include "wallet_rpc_server_commands_defs.h"
 #include "wallet2.h"
@@ -154,7 +155,7 @@ namespace tools
 
       wallet2 *m_wallet;
       std::string m_wallet_dir;
-      std::string rpc_login_filename;
+      tools::private_file rpc_login_file;
       std::atomic<bool> m_stop;
       bool m_trusted_daemon;
       epee::net_utils::http::http_simple_client m_http_client;