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

[PhanLe1010]

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

[coderabbitai]

Walkthrough

The changes modify the encryption process in the crypto.go file by introducing a new function, isDeviceEncrypted, which checks if a device is already encrypted using a namespace executor. The EncryptVolume function now calls this helper function; if an error occurs during this check, a warning is logged and the error is returned, and if the device is already encrypted, an informational log is output and the function exits early. Additionally, the import for github.com/longhorn/longhorn-manager/types has been reorganized.

Changes

File	Summary
csi/crypto/crypto.go	- Added isDeviceEncrypted function to check device encryption status. - Modified EncryptVolume for error handling and early exit if already encrypted. - Reorganized import for .../longhorn-manager/types.

Sequence Diagram(s)

sequenceDiagram
    participant Caller
    participant EncryptVolume
    participant isDeviceEncrypted
    participant Logger

    Caller->>EncryptVolume: Request encryption (devicePath)
    EncryptVolume->>isDeviceEncrypted: Check if device is encrypted
    isDeviceEncrypted-->>EncryptVolume: Returns (error or true/false)
    alt Error during check
        EncryptVolume->>Logger: Log warning
        EncryptVolume-->>Caller: Return error
    else Device already encrypted
        EncryptVolume->>Logger: Log info (skip encryption)
        EncryptVolume-->>Caller: Return nil
    else Device not encrypted
        EncryptVolume->>Logger: Proceed with encryption process
        EncryptVolume-->>Caller: Continue with encryption
    end

Loading

Possibly related PRs

• feat(crypto): v2 volume encryption #3438: Updates related to volume encryption logic, specifically accommodating new parameters in encryption functions, which share context with the modifications introduced by the new isDeviceEncrypted function.

Suggested reviewers

• derekbit
• shuo-wu

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[derekbit]

LGTM

[PhanLe1010]

Btw, please let me know if you have better idea than the cryptsetup isLuks solution @derekbit @shuo-wu @c3y1huang @mantissahz

[derekbit]

@PhanLe1010 go fmt failed

[PhanLe1010]

@PhanLe1010 go fmt failed

Fixed

[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (2)

csi/crypto/crypto.go (2)

194-201: LGTM! Critical fix for race condition.

The new function correctly uses cryptsetup isLuks to accurately determine the encryption status of a device, addressing the root cause of data loss during re-encryption. The implementation properly handles namespace isolation and error propagation.

This change is crucial as it:

1. Prevents race conditions during engine crashes
2. Provides reliable device encryption detection
3. Avoids data loss from incorrect re-encryption

---

88-97: LGTM! Enhanced error handling and data protection.

The changes correctly prevent data loss by checking encryption status before proceeding. The error handling and logging provide good observability.

Consider enhancing the log message in line 90 to include more context:

-		logrus.WithError(err).Warnf("Failed to check IsDeviceEncrypted before encrypting volume %v", devicePath)
+		logrus.WithError(err).Warnf("Failed to check encryption status before encrypting volume %v. This might indicate issues with cryptsetup or device access", devicePath)

📜 Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 5f9ec86 and e3d1e9f.

⛔ Files ignored due to path filters (1)

• vendor/github.com/longhorn/go-common-libs/ns/crypto.go is excluded by !vendor/**

📒 Files selected for processing (1)

• csi/crypto/crypto.go (3 hunks)

⏰ Context from checks skipped due to timeout of 90000ms (2)

• GitHub Check: Build binaries
• GitHub Check: Summary

🔇 Additional comments (1)

csi/crypto/crypto.go (1)

14-15: LGTM!

The import reorganization follows Go's standard grouping practices.

[derekbit]

@mergify backport v1.8.x v1.7.x

[mergify]

backport v1.8.x v1.7.x

✅ Backports have been created

• #3567 fix: data lost caused by Longhorn CSI plugin doing a wrong re-encryption of volume in rare race condition (backport #3566) has been created for branch v1.8.x
• #3568 fix: data lost caused by Longhorn CSI plugin doing a wrong re-encryption of volume in rare race condition (backport #3566) has been created for branch v1.7.x but encountered conflicts