fix tar extraction add path validation to prevent escape from destination

[odaysec]

Description

This fixes addresses path traversal vulnerabilities in tar archive extraction within the kind codebase. Without proper validation, specially crafted tar entries could escape the intended extraction directory and overwrite arbitrary files on the host system. This PR introduces safeguards to ensure that extracted files remain confined to the target directory.

kind/pkg/cluster/internal/logs/logs.go

Lines 77 to 97 in f20102c

	abs := filepath.Join(dir, rel)
	switch f.Typeflag {
	case tar.TypeReg:
	wf, err := os.OpenFile(abs, os.O_CREATE|os.O_RDWR, os.FileMode(f.Mode))
	if err != nil {
	return err
	}
	n, err := io.Copy(wf, tr)
	if closeErr := wf.Close(); closeErr != nil && err == nil {
	err = closeErr
	}
	if err != nil {
	return errors.Errorf("error writing to %s: %v", abs, err)
	}
	if n != f.Size {
	return errors.Errorf("only wrote %d bytes to %s; expected %d", n, abs, f.Size)
	}
	case tar.TypeDir:
	if _, err := os.Stat(abs); err != nil {
	if err := os.MkdirAll(abs, 0755); err != nil {

• Issue: Tar archive entries are written to paths derived directly from the archive without validation. Attackers could craft entries with .. or absolute paths to escape the destination directory.

  • Compute the absolute path of the intended extraction target using filepath.Abs and filepath.Clean.
  • Verify that the target path begins with the cleaned absolute destination directory path.
  • Skip extraction (or return an error) for any entry that falls outside of the allowed directory.
  • Ensure this check is performed before any file system operations (e.g., os.Create, os.MkdirAll).

kind/pkg/build/nodeimage/internal/kube/tar.go

Lines 44 to 49 in f20102c

	filepath.Join(destDirectory, filepath.Dir(hdr.Name)), os.FileMode(0o755),
	); err != nil {
	return fmt.Errorf("creating image directory structure: %w", err)
	}
	f, err := os.Create(filepath.Join(destDirectory, hdr.Name))

• Issue: Similar to untar, the function does not validate hdr.Name, allowing malicious tar entries to escape the intended destination.
  • After joining hdr.Name with the target directory, normalize the path using filepath.Clean.
  • Confirm that the cleaned path remains within the cleaned target directory.
  • Reject or skip entries containing absolute paths or .. segments that lead outside the extraction directory.
  • Added a check using strings.HasPrefix(cleanedPath, cleanedDestDir + string(os.PathSeparator)) to enforce confinement.

Notes Refferences

• No new dependencies were added; the fix leverages existing filepath, os, and strings packages.
• The behavior of normal, well-formed tarballs remains unchanged.
• Malicious or malformed entries are safely rejected.

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @odaysec. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[odaysec]

/ok-to-test

[k8s-ci-robot]

@odaysec: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

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[stmcginnis]

Do you see a way where this is exposed in a way that could be exploited? Or was this just an AI recommendation?

[BenTheElder]

/ok-to-test

Do you see a way where this is exposed in a way that could be exploited? Or was this just an AI recommendation?

ummm if you have a malicious process running in the kind node which is bad enough on it's own, but perhaps sandboxed into say, a limactl vm, then this allow overwriting on the host as the host user IF the user calls kind export logs (which is pretty common)

for the other one, where you're downloading a kubernetes release, if that is malicious then you're probably in pretty bad shape already, but we should still mitigate it.

[BenTheElder]

this should be hoisted out of the loop?

[k8s-ci-robot]

@odaysec: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kind-test	1e225b8	link	true	/test pull-kind-test
pull-kind-e2e-kubernetes	1e225b8	link	true	/test pull-kind-e2e-kubernetes
pull-kind-conformance-parallel-dual-stack-ipv4-ipv6	1e225b8	link	true	/test pull-kind-conformance-parallel-dual-stack-ipv4-ipv6
pull-kind-conformance-parallel-ga-only	1e225b8	link	true	/test pull-kind-conformance-parallel-ga-only
pull-kind-conformance-parallel-ipv6	1e225b8	link	true	/test pull-kind-conformance-parallel-ipv6
pull-kind-build	1e225b8	link	true	/test pull-kind-build
pull-kind-e2e-kubernetes-1-32	1e225b8	link	true	/test pull-kind-e2e-kubernetes-1-32
pull-kind-e2e-kubernetes-1-34	1e225b8	link	true	/test pull-kind-e2e-kubernetes-1-34
pull-kind-e2e-kubernetes-1-31	1e225b8	link	true	/test pull-kind-e2e-kubernetes-1-31
pull-kind-verify	1e225b8	link	true	/test pull-kind-verify
pull-kind-e2e-kubernetes-1-33	1e225b8	link	true	/test pull-kind-e2e-kubernetes-1-33

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[BenTheElder]

I think we should probably be looking at https://go.dev/blog/osroot in the future

unfortunately it would make go 1.24 the minimum version to build kind, which is a little aggressive at the moment