[libcxx] r337659 - Harden copy_file even more.

[Eric Fiselier via cfe-commits]

Author: ericwf
Date: Sun Jul 22 14:15:15 2018
New Revision: 337659

URL: http://llvm.org/viewvc/llvm-project?rev=337659&view=rev
Log:
Harden copy_file even more.

This patch removes the O_CREAT open flag when we first
attempt to open the destination file but we expect it to
already exist.

This theoretically avoids the possibility that it was removed
between when we first stat'ed it, and when we attempt to open it.

Modified:
    libcxx/trunk/src/experimental/filesystem/operations.cpp

Modified: libcxx/trunk/src/experimental/filesystem/operations.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/src/experimental/filesystem/operations.cpp?rev=337659&r1=337658&r2=337659&view=diff
==============================================================================
--- libcxx/trunk/src/experimental/filesystem/operations.cpp (original)
+++ libcxx/trunk/src/experimental/filesystem/operations.cpp Sun Jul 22 14:15:15 2018
@@ -716,7 +716,7 @@ bool __copy_file(const path& from, const
   if (to_exists && skip_existing)
     return false;
 
-  auto ShouldCopy = [&]() {
+  bool ShouldCopy = [&]() {
     if (to_exists && update_existing) {
       auto from_time = detail::extract_mtime(from_stat);
       auto to_time = detail::extract_mtime(to_stat_path);
@@ -730,13 +730,15 @@ bool __copy_file(const path& from, const
     if (!to_exists || overwrite_existing)
       return true;
     return Error(make_error_code(errc::file_exists));
-  };
-  if (!ShouldCopy())
+  }();
+  if (!ShouldCopy)
     return false;
 
   // Don't truncate right away. We may not be opening the file we originally
   // looked at; we'll check this later.
-  int to_open_flags = O_WRONLY | O_CREAT;
+  int to_open_flags = O_WRONLY;
+  if (!to_exists)
+    to_open_flags |= O_CREAT;
   FileDescriptor to_fd = FileDescriptor::create_with_status(
       &to, m_ec, to_open_flags, from_stat.st_mode);
   if (m_ec)
@@ -745,6 +747,7 @@ bool __copy_file(const path& from, const
   if (to_exists) {
     // Check that the file we initially stat'ed is equivalent to the one
     // we opened.
+    // FIXME: report this better.
     if (!detail::stat_equivalent(to_stat_path, to_fd.get_stat()))
       return Error(make_error_code(errc::bad_file_descriptor));
 
@@ -761,7 +764,6 @@ bool __copy_file(const path& from, const
   }
 
   return true;
-
 }
 
 void __copy_symlink(const path& existing_symlink, const path& new_symlink,