Avoid closing directory we're iterating

[ekohl]

This starts with reverting #39 because it's broken and caused a regression. Then I've taken my commits from puppetlabs/puppet#9546.

Ruby 3.4 started error checking directory access and starts to raise Errno::EBADF.

This particular loop iterates on all open file descriptors and one is the directory listing from Dir.foreach.

In the past this could have led to leaked file descriptors, but it's unlikely since it's likely the last opened file descriptor and have the highest number.

Link: ruby/ruby@f2919bd
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2349352

[ekohl]

Looking at #41 I wonder if we should explicitly exclude the FDs that we want to keep open:

Suggested change

	ignore_fds = ['.', '..', d.fileno.to_s]
	d.each_child do |f|
	next if ignore_fds.include?(f) || f.to_i < 3
	ignore_fds = ['.', '..', stdin.fileno.to_s, stdout.fileno.to_s, stderr.fileno.to_s, d.fileno.to_s]
	d.each_child do |f|
	next if ignore_fds.include?(f)

This version is probably safer. Not sure if it's valid to have no stdin, stdout or stderr.

Suggested change

	ignore_fds = ['.', '..', d.fileno.to_s]
	d.each_child do |f|
	next if ignore_fds.include?(f) || f.to_i < 3
	ignore_fds = ['.', '..'] + [stdin, stdout, stderr, d].filter_map { |f| f&.fileno&.to_s }
	d.each_child do |f|
	next if ignore_fds.include?(f)

What makes me hesitant is that I don't know

[nmburgan]

I'm a little worried we're playing whack-a-mole with things we want to filter out and I'm not sure how to be sure we're being exhaustive about it.

[ekohl]

IMHO this is much better than looking at .to_i < 3 and assuming that those file descriptors are stdin, stdout and stderr since it is explicit about what's going on.

[ekohl]

And I just noticed this repo doesn't run any of the tests, but when I locally run it I did break them:

puppet/spec/unit/util_spec.rb

Lines 597 to 665 in 13dd914

	describe "safe_posix_fork", unless: Puppet::Util::Platform.windows? || Puppet::Util::Platform.jruby? do
	let(:pid) { 5501 }
	before :each do
	# Most of the things this method does are bad to do during specs. :/
	allow(Kernel).to receive(:fork).and_return(pid).and_yield
	allow($stdin).to receive(:reopen)
	allow($stdout).to receive(:reopen)
	allow($stderr).to receive(:reopen)
	# ensure that we don't really close anything!
	allow(IO).to receive(:new)
	end
	it "should close all open file descriptors except stdin/stdout/stderr when /proc/self/fd exists" do
	# This is ugly, but I can't really think of a better way to do it without
	# letting it actually close fds, which seems risky
	fds = [".", "..","0","1","2","3","5","100","1000"]
	fds.each do |fd|
	if fd == '.' || fd == '..'
	next
	elsif ['0', '1', '2'].include? fd
	expect(IO).not_to receive(:new).with(fd.to_i)
	else
	expect(IO).to receive(:new).with(fd.to_i).and_return(double('io', close: nil))
	end
	end
	dir_expectation = receive(:foreach).with('/proc/self/fd')
	fds.each do |fd|
	dir_expectation = dir_expectation.and_yield(fd)
	end
	allow(Dir).to dir_expectation
	Puppet::Util.safe_posix_fork
	end
	it "should close all open file descriptors except stdin/stdout/stderr when /proc/self/fd doesn't exist" do
	# This is ugly, but I can't really think of a better way to do it without
	# letting it actually close fds, which seems risky
	(0..2).each {|n| expect(IO).not_to receive(:new).with(n)}
	(3..256).each {|n| expect(IO).to receive(:new).with(n).and_return(double('io', close: nil)) }
	allow(Dir).to receive(:foreach).with('/proc/self/fd').and_raise(Errno::ENOENT)
	Puppet::Util.safe_posix_fork
	end
	it "should close all open file descriptors except stdin/stdout/stderr when /proc/self is not a directory" do
	# This is ugly, but I can't really think of a better way to do it without
	# letting it actually close fds, which seems risky
	(0..2).each {|n| expect(IO).not_to receive(:new).with(n)}
	(3..256).each {|n| expect(IO).to receive(:new).with(n).and_return(double('io', close: nil)) }
	allow(Dir).to receive(:foreach).with('/proc/self/fd').and_raise(Errno::ENOTDIR)
	Puppet::Util.safe_posix_fork
	end
	it "should fork a child process to execute the block" do
	expect(Kernel).to receive(:fork).and_return(pid).and_yield
	Puppet::Util.safe_posix_fork do
	"Fork this!"
	end
	end
	it "should return the pid of the child process" do
	expect(Puppet::Util.safe_posix_fork).to eq(pid)
	end
	end