[ruby-core:91216] [Ruby trunk Bug#15555] Dir.mktmpdir checks permissions and raise ArgumentError after yielding to block (ensure) & leaks allocated tempdir

Issue #15555 has been reported by kbogtob (Karim Bogtob).

----------------------------------------
Bug #15555: Dir.mktmpdir checks permissions and raise ArgumentError after yielding to block (ensure) & leaks allocated tempdir
https://bugs.ruby-lang.org/issues/15555

* Author: kbogtob (Karim Bogtob)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux-gnu]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
The current implementation of the Dir.mktmpdir is the following:

```ruby
def Dir.mktmpdir(prefix_suffix=nil, *rest)
  path = Tmpname.create(prefix_suffix || "d", *rest) {|n| mkdir(n, 0700)}
  if block_given?
    begin
      yield path
    ensure
      stat = File.stat(File.dirname(path))
      if stat.world_writable? and !stat.sticky?
        raise ArgumentError, "parent directory is world writable but not sticky"
      end
      FileUtils.remove_entry path
    end
  else
    path
  end
end
```

When used explicitly with a directory, it raises an ArgumentError when the directory is world writable (File::Stat#world_writable?) but not sticky (File::Stat#sticky?). This is a normal behavior. But with how the method is written, the behavior is inconsistent and raises an ArgumentError only when using it with the block form. Worse, it raises the error in the ensure block instead of the first thing done in the method. So it raises the ArgumentError **after** it yields to the block, so after the job is already done.

Proof:
```ruby
irb(main):001:0> puts `ls -la /tmp`
total 4
drwxrwsrwx.  2 root 1000090000    6 Jan 22 10:02 .
drwxr-xr-x. 18 root root       4096 Jan 22 09:58 ..
=> nil
irb(main):002:0> # /tmp is non sticky but world writable
irb(main):003:0* Dir.mktmpdir(nil, '/tmp') do |tmpdir|
irb(main):004:1*   puts "Hello, I'm using #{tmpdir}"
irb(main):005:1> end
Hello, I'm using /tmp/d20190122-26-5biuz2
ArgumentError: parent directory is world writable but not sticky
  from /opt/rh/rh-ruby24/root/usr/share/ruby/tmpdir.rb:93:in `mktmpdir'
  from (irb):3
  from /opt/rh/rh-ruby24/root/usr/bin/irb:11:in `<top (required)>'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli/exec.rb:74:in `load'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli/exec.rb:74:in `kernel_load'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli/exec.rb:27:in `run'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli.rb:362:in `exec'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli.rb:22:in `dispatch'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/cli.rb:13:in `start'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/exe/bundle:30:in `block in <top (required)>'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/lib/bundler/friendly_errors.rb:121:in `with_friendly_errors'
  from /opt/rh/rh-ruby24/root/usr/local/share/gems/gems/bundler-1.15.4/exe/bundle:22:in `<top (required)>'
  from /opt/rh/rh-ruby24/root/usr/bin/bundle:23:in `load'
  from /opt/rh/rh-ruby24/root/usr/bin/bundle:23:in `<main>'
irb(main):006:0> puts `ls -la /tmp`
total 4
drwxrwsrwx.  3 root       1000090000   33 Jan 22 10:03 .
drwxr-xr-x. 18 root       root       4096 Jan 22 09:58 ..
drwx--S---.  2 1000090000 1000090000    6 Jan 22 10:03 d20190122-26-5biuz2
=> nil
```

We can also see that the allocated directory **remains** after the exception is raised as the implementation raised in the ensure block.

An advisable implementation would be:
```ruby
def Dir.mktmpdir(prefix_suffix=nil, *rest)
  path = Tmpname.create(prefix_suffix || "d", *rest) {|n| mkdir(n, 0700)}
  stat = File.stat(File.dirname(path))
  if stat.world_writable? and !stat.sticky?
    raise ArgumentError, "parent directory is world writable but not sticky"
  end
  
  if block_given?
    begin
      yield path
    ensure
      FileUtils.remove_entry path
    end
  else
    path
  end
end
```
This way, it will make the checks first and raise directly. And no temporary directory will be leaked with the block form.

As there is no maintainer for this lib, I can make a pull request with the following changes (with unit tests) if I'm asked to.



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