fix: data lost caused by Longhorn CSI plugin doing a wrong re-encryption of volume in rare race condition (backport #3566)

[mergify]

longhorn/longhorn#10416

RCA

This happens with encrypted volume only

While Longhorn CSI plugin is doing NodeStageVolume, if the Longhorn engine crash right before GetDiskFormat and recover quickly after that, the following race condition can happen:

1. When engine is crash, the engine removes the Longhorn device at /dev/longhorn/volume-name
2. Because the device path is gone, getDiskFormat returns empty value for diskFormat and nil error. Ref

   longhorn-manager/vendor/k8s.io/mount-utils/mount_linux.go

   Lines 687 to 693 in 5f9ec86

   	if exit.ExitStatus() == 2 {
   	// Disk device is unformatted.
   	// For `blkid`, if the specified token (TYPE/PTTYPE, etc) was
   	// not found, or no (specified) devices could be identified, an
   	// exit code of 2 is returned.
   	return "", nil
   	}

3. Now engine is recovered, so it recreates the device at /dev/longhorn/volume-name
4. However, due to diskFormat having empty value, Longhorn re-encrypts the volume which wipes out the all data. Ref

   longhorn-manager/csi/node_server.go

   Lines 513 to 517 in 5f9ec86

   	if diskFormat == "" {
   	if err := crypto.EncryptVolume(devicePath, passphrase, cryptoParams); err != nil {
   	return nil, status.Error(codes.Internal, err.Error())
   	}
   	}

5. Finally, Longhorn cannot detect a filesystem for the volume any more so it reformat the filesystem
6. The root cause of the issue is that getDiskFormat is using blkid. The blkid command cannot differentiate 2 cases: the device doesn't exist VS the device doesn't have filesystem inside it

Proposal

Use cryptsetup isLuks instead. It can differentiate between:

1. The device is already encrypted -> return exit code 0
2. The device is not encrypted -> return exit code 1
3. All other errors -> return exit code 4

Ref: https://gitlab.com/cryptsetup/cryptsetup/-/blob/main/FAQ.md?plain=1#L2848

With this proposal, we can safely make decision of only doing encryption in the 2nd case

Additional documentation or context

We were discussing of the below ideas with @derekbit and @shuo-wu but it seems cannot remove the race condition 100%

Idea 1: Check if the device path exist before doing GetDiskFormat

_, err := os.stat(devicePath)
if err != nil {
    return err
}

formatMounter.GetDiskFormat(devicePath)

-> Cannot avoid the race condition as the device can still disappear before GetDiskFormat and re-appear after GetDiskFormat

Idea 2: Check if the device path exist after doing GetDiskFormat

formatMounter.GetDiskFormat(devicePath)

_, err := os.stat(devicePath)
if err != nil {
    return err
}

-> Cannot avoid the race condition as the device can still disappear before GetDiskFormat and re-appear after GetDiskFormat

---

This is an automatic backport of pull request #3566 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 72c9173 has failed:

On branch mergify/bp/v1.7.x/pr-3566
Your branch is up to date with 'origin/v1.7.x'.

You are currently cherry-picking commit 72c91734.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   vendor/github.com/longhorn/go-common-libs/ns/crypto.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   csi/crypto/crypto.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[coderabbitai]

Important

Review skipped

Bot user detected.

To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

---

Thank you for using CodeRabbit. We offer it for free to the OSS community and would appreciate your support in helping us grow. If you find it useful, would you consider giving us a shout-out on your favorite social media?

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

🪧 Tips

Chat

There are 3 ways to chat with CodeRabbit:

• Review comments: Directly reply to a review comment made by CodeRabbit. Example:
  • I pushed a fix in commit <commit_id>, please review it.
  • Generate unit testing code for this file.
  • Open a follow-up GitHub issue for this discussion.
• Files and specific lines of code (under the "Files changed" tab): Tag @coderabbitai in a new review comment at the desired location with your query. Examples:
  • @coderabbitai generate unit testing code for this file.
  • @coderabbitai modularize this function.
• PR comments: Tag @coderabbitai in a new PR comment to ask questions about the PR branch. For the best results, please provide a very specific query, as very limited context is provided in this mode. Examples:
  • @coderabbitai gather interesting stats about this repository and render them as a table. Additionally, render a pie chart showing the language distribution in the codebase.
  • @coderabbitai read src/utils.ts and generate unit testing code.
  • @coderabbitai read the files in the src/scheduler package and generate a class diagram using mermaid and a README in the markdown format.
  • @coderabbitai help me debug CodeRabbit configuration file.

Note: Be mindful of the bot's finite context window. It's strongly recommended to break down tasks such as reading entire modules into smaller chunks. For a focused discussion, use review comments to chat about specific files and their changes, instead of using the PR comments.

CodeRabbit Commands (Invoked using PR comments)

• @coderabbitai pause to pause the reviews on a PR.
• @coderabbitai resume to resume the paused reviews.
• @coderabbitai review to trigger an incremental review. This is useful when automatic reviews are disabled for the repository.
• @coderabbitai full review to do a full review from scratch and review all the files again.
• @coderabbitai summary to regenerate the summary of the PR.
• @coderabbitai generate docstrings to generate docstrings for this PR. (Beta)
• @coderabbitai resolve resolve all the CodeRabbit review comments.
• @coderabbitai configuration to show the current CodeRabbit configuration for the repository.
• @coderabbitai help to get help.

Other keywords and placeholders

• Add @coderabbitai ignore anywhere in the PR description to prevent this PR from being reviewed.
• Add @coderabbitai summary to generate the high-level summary at a specific location in the PR description.
• Add @coderabbitai anywhere in the PR title to generate the title automatically.

CodeRabbit Configuration File (.coderabbit.yaml)

• You can programmatically configure CodeRabbit by adding a .coderabbit.yaml file to the root of your repository.
• Please see the configuration documentation for more information.
• If your editor has YAML language server enabled, you can add the path at the top of this file to enable auto-completion and validation: # yaml-language-server: $schema=https://coderabbit.ai/integrations/schema.v2.json

Documentation and Community

• Visit our Documentation for detailed information on how to use CodeRabbit.
• Join our Discord Community to get help, request features, and share feedback.
• Follow us on X/Twitter for updates and announcements.

[mergify]

This pull request is now in conflict. Could you fix it @mergify[bot]? 🙏