Double Free in Buffalo

Double free vulnerabilities in Buffalo applications occur when memory allocated for a resource is freed more than once, typically through multiple execution paths or error conditions. In Buffalo's Go-based web framework, these issues commonly arise in middleware chains, database connection handling, and JSON request processing.

A classic Buffalo double free scenario involves database transactions. Consider this problematic pattern:

func (c Context) CreateUser() error {
    tx, err := c.Tx() 
    if err != nil {
        return err
    }
    defer tx.Rollback()
    
    user := &User{Name: c.Param("name")}
    err = tx.Create(user)
    if err != nil {
        return err // Transaction rolled back here
    }
    
    // Another error path that also rolls back
    if user.Name == "test" {
        tx.Rollback() // Double free! Already rolled back by defer
        return errors.New("test user not allowed")
    }
    
    err = tx.Commit()
    if err != nil {
        tx.Rollback() // Triple free risk!
        return err
    }
    
    return nil
}

The defer statement and explicit Rollback calls create multiple free attempts on the same transaction object. This manifests as:

• Database connection pool corruption
• Application panics with "sql: transaction has already been committed or rolled back"
• Memory corruption leading to undefined behavior
• Potential information disclosure through heap spraying
• Denial of service through connection exhaustion

Another Buffalo-specific pattern involves JSON request handling with early returns:

func (c Context) UpdateProfile() error {
    var profile Profile
    if err := c.Bind(&profile); err != nil {
        return err // JSON decoder resources not freed
    }
    
    // Early return without cleanup
    if profile.Age < 0 {
        return c.Error(400, "Invalid age")
    }
    
    // Resource cleanup needed here
    return c.Render(200, r.JSON(profile))
}

Middleware chains in Buffalo can also propagate double free conditions when error handling isn't centralized:

func AuthMiddleware(next buffalo.Handler) buffalo.Handler {
    return func(c Context) error {
        if !isAuthenticated(c) {
            c.Response().WriteHeader(401)
            return errors.New("unauthorized") // Response writer not reset
        }
        
        // Next handler might also write to response
        return next(c)
    }
}

Detecting double free vulnerabilities in Buffalo applications requires a multi-layered approach combining static analysis, runtime monitoring, and automated scanning.

Static analysis using Go's built-in tools can catch many double free patterns:

go vet -vettool=$(which govulncheck) ./...
staticcheck ./...
golangci-lint run --enable-all

Dynamic detection during testing involves resource tracking:

type trackedResource struct {
    id       string
    freed    bool
    freedAt  time.Time
    freedBy  string
}

var resourceTracker = sync.Map{}

func trackResource(id string) {
    resourceTracker.Store(id, &trackedResource{id: id, freed: false})
}

func freeResource(id string, freedBy string) {
    if v, ok := resourceTracker.Load(id); ok {
        r := v.(*trackedResource)
        if r.freed {
            log.Printf("DOUBLE FREE DETECTED: %s freed by %s (previously freed by %s)", 
                id, freedBy, r.freedBy)
        }
        r.freed = true
        r.freedAt = time.Now()
        r.freedBy = freedBy
    }
}

middleBrick's API security scanner specifically detects double free vulnerabilities in Buffalo applications through black-box testing. The scanner:

• Identifies endpoints with multiple error return paths
• Tests transaction handling with various error conditions
• Monitors resource allocation and deallocation patterns
• Detects inconsistent cleanup across success/failure paths

middleBrick's continuous monitoring catches these issues by:

middlebrick scan https://api.yourservice.com --tests=transaction,cleanup,resource-management

The scanner reports findings with severity levels and specific remediation guidance for Buffalo's Go patterns.

Buffalo's idiomatic Go patterns provide several mechanisms to prevent double free vulnerabilities. The key principle is centralized resource management with clear ownership semantics.

For database transaction handling, use this safe pattern:

func (c Context) CreateUser() error {
    tx, err := c.Tx()
    if err != nil {
        return err
    }
    
    // Single point of cleanup
    cleanup := func() {
        if tx != nil {
            tx.Rollback()
            tx = nil
        }
    }
    defer cleanup()
    
    user := &User{Name: c.Param("name")}
    if err := tx.Create(user); err != nil {
        return err
    }
    
    if user.Name == "test" {
        return errors.New("test user not allowed")
    }
    
    if err := tx.Commit(); err != nil {
        return err
    }
    
    // Prevent rollback after successful commit
    tx = nil
    return nil
}

For JSON request handling, implement proper cleanup:

func (c Context) UpdateProfile() error {
    var profile Profile
    if err := c.Bind(&profile); err != nil {
        return err
    }
    
    // Validate before processing
    if profile.Age < 0 {
        return c.Error(400, "Invalid age")
    }
    
    // Process and render
    return c.Render(200, r.JSON(profile))
}

Middleware should use error wrapping to preserve context:

func AuthMiddleware(next buffalo.Handler) buffalo.Handler {
    return func(c Context) error {
        if !isAuthenticated(c) {
            return c.Error(401, "unauthorized")
        }
        
        // Let next handler handle its own errors
        return next(c)
    }
}

For file handling in Buffalo handlers:

func (c Context) UploadFile() error {
    file, err := c.File("upload")
    if err != nil {
        return err
    }
    defer file.Close() // Single cleanup point
    
    // Process file
    defer func() {
        if file != nil {
            file.Close()
        }
    }()
    
    // No other close() calls allowed
    return c.Render(200, r.JSON(map[string]string{"status": "uploaded"}))
}

Buffalo's error handling utilities help centralize cleanup:

func (c Context) ProcessData() error {
    var result []byte
    var err error
    
    // Using Buffalo's error handling
    if err = processStep1(); err != nil {
        return c.Error(500, err)
    }
    
    if err = processStep2(); err != nil {
        return c.Error(500, err)
    }
    
    return c.Render(200, r.JSON(map[string]interface{}{"data": result}))
}