mkdir: Fix stack overflow with deeply nested directories

[naoNao89]

Fixes #8945

mkdir -p with 200+ nested directories? Segfault. The recursive implementation ate stack frames like candy.

Fix
Swapped recursion for iteration. Collect parent directories into a vector (heap), create them root-to-leaf. Constant stack space, infinite depth.

Proof It Works

# Before: Segmentation fault: 11
$ ulimit -s 128
$ ./target/release/coreutils mkdir -p `python3 -c 'print("a/" * 250)'`
Segmentation fault: 11

AFTER THE FIX:

$ ulimit -s 128  
$ ./target/release/coreutils mkdir -p `python3 -c 'print("a/" * 250)'`
(success - directories created)

$ ulimit -s 128
$ ./target/release/coreutils mkdir -p `python3 -c 'print("a/" * 400)'`  
(success - even deeper nesting works)

Our changes touch code originally by 8ccc45c (2022)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[codspeed-hq]

CodSpeed Performance Report

Merging #8947 will not alter performance

_{Comparing naoNao89:fix/mkdir-stack-overflow (3bf5ab6) with main (85a7812)}

Summary

✅ 106 untouched
⏩ 73 skipped¹

Footnotes

1. 73 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[sylvestre]

please ignore it on top of the file
don't need to be global

[cakebaker]

Is this test supposed to fail without the changes made to mkdir.rs?

[cakebaker]

You can omit the condition if you use a PathBuf instead of a String:

Suggested change

	let mut path = String::new();
	for i in 0..depth {
	if i > 0 {
	path.push('/');
	}
	path.push_str(dir_name);
	}
	let mut path = PathBuf::new();
	for _ in 0..depth {
	path.push(dir_name);
	}

Or you could use a functional approach:

    let path = Path::new(dir_name).join(std::iter::repeat(dir_name).take(depth).collect::<PathBuf>());

[cakebaker]

It might be clearer to use components():

Suggested change

	let has_dotdot = parent
	.as_os_str()
	.as_encoded_bytes()
	.windows(2)
	.any(|w| w == b"..");
	let has_dotdot = parent.components().any(|c| c.as_os_str() == "..");

[cakebaker]

The comment should be moved to create_single_dir as this function no longer contains any Windows-specific code.

Suggested change

	// `is_parent` argument is not used on windows
	#[allow(unused_variables)]

[cakebaker]

You can re-arrange things a bit and get rid of the unwrap_or:

Suggested change

	let ends_with_dotdot = path
	.components()
	.next_back()
	.map(|c| matches!(c, std::path::Component::ParentDir))
	.unwrap_or(false);
	let ends_with_dotdot = matches!(
	path.components().next_back(),
	Some(std::path::Component::ParentDir)
	);