[Bug libstdc++/85773] New: Embedded nulls in filesystem::path cause problems

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85773

            Bug ID: 85773
           Summary: Embedded nulls in filesystem::path cause problems
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#include <filesystem>
int main()
{
  std::filesystem::create_directories("a/b");
  std::string s("a\0/..", 5);
  for (auto f : std::filesystem::recursive_directory_iterator(s))
  { }
}

$ GCC 8 -std=c++17 null.cc -lstdc++fs
$ ./a.out
terminate called after throwing an instance of
'std::filesystem::__cxx11::filesystem_error'
  what():  filesystem error: cannot increment recursive directory iterator: Too
many open files
Aborted (core dumped)


The problem is that we call opendir(pathname.c_str()) which only reads up to
the null terminator, so we open "a"  but then the pathname for the first
element in the iteration sequence is formed by concatenating "a\0/.." / "b" and
then recursing by calling opendir(path("a\0/../b").c_str()) which opens "a"
again. This keeps looping, opening "a" every time until we reach the ulimit for
open files.