6.4 Resource protection and access control
4 min read•august 15, 2024
Resource protection and access control are crucial aspects of operating system security. These mechanisms safeguard system resources from unauthorized access and regulate user and process permissions. By implementing principles like least privilege and , OS designers create robust security frameworks.
Access control can be implemented through various methods, including , , and reference monitors. These approaches offer different trade-offs between security, flexibility, and ease of management, allowing OS designers to choose the best fit for their specific requirements.
Resource Protection and Access Control
Principles of Resource Protection
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- Resource protection safeguards system resources (memory, files, devices) from unauthorized access or modification by users or processes
- Access control regulates which users or processes can access specific resources and what operations they can perform
- Principle of least privilege grants users and processes the minimum level of access necessary to perform their tasks
- Separation of privilege requires multiple conditions or users to be satisfied before executing critical system operations
- , , and (AAA) serve as three key components of access control in operating systems
- Authentication verifies the identity of users or processes
- Authorization determines the level of access granted to authenticated entities
- Accounting tracks and logs access attempts and resource usage
Access Control Implementation Methods
- Access control matrices represent permissions as a table with subjects (users/processes) as rows and objects (resources) as columns
- Capability lists associate unforgeable tokens (capabilities) with specific access rights to resources
- Provides fine-grained control over resource access
- Simplifies permission management and revocation
- concept defines an abstract machine mediating all access to objects by subjects
- Ensures complete mediation of access requests
- Implements the principle of least privilege
- Verifies the integrity of access control mechanisms
Discretionary vs Mandatory Access Control
Discretionary Access Control (DAC)
- Allows resource owners to determine access rights for their resources
- Provides users with flexibility in managing permissions
- Access rights can be passed from one user to another
- Potentially leads to unintended access propagation
- Examples of DAC systems include:
- Traditional Unix
- Windows NTFS file permissions
Mandatory Access Control (MAC)
- Enforces system-wide policies that cannot be altered by individual users
- Provides stricter control over resource access
- Uses security labels or clearance levels to determine access rights
- Often implemented in high-security or military environments
- Key MAC models include:
- Bell-LaPadula model (focuses on confidentiality)
- Biba model (emphasizes data integrity)
- Principle of tranquility states that the security level of an object should not change during normal operation
Hybrid Access Control Models
- (RBAC) assigns permissions to roles rather than individual users
- Simplifies access management in large organizations
- Allows for easy scaling and modification of access rights
- (ABAC) uses attributes of users, resources, and environment to determine access rights
- Provides more flexible and context-aware access control
- Allows for complex policy definitions based on multiple factors
Access Control Mechanisms and Implementation
File Permissions in Unix-like Systems
- Combine read, write, and execute permissions for owner, group, and others
- Example: rwxr-xr-x (owner has full permissions, group and others can read and execute)
- Modify permissions using the chmod command
- Symbolic notation (u+x adds execute permission for the owner)
- Octal notation (755 sets rwxr-xr-x permissions)
- Special permission types:
- (t) prevents deletion of files by non-owners in shared directories
- (s) allows execution of files with the permissions of the file owner or group
Access Control Lists (ACLs)
- Provide more granular control over file permissions
- Allow specific permissions for individual users or groups
- Windows NTFS file systems use ACLs to manage file and directory permissions
- Include advanced permissions (Take Ownership, Change Permissions)
- Linux systems support ACLs through extended attributes
- Managed using setfacl and getfacl commands
Capability-based Systems
- Use unforgeable tokens (capabilities) that grant specific access rights to resources
- Provide fine-grained approach to access control
- Simplify permission management and revocation
- Examples of :
- KeyKOS operating system
- EROS (Extremely Reliable Operating System)
Security Implications of Access Control Policies
Policy Granularity and Balance
- Overly permissive policies can lead to unauthorized access and data breaches
- Excessively restrictive policies may impede legitimate user activities
- Can result in users creating workarounds that compromise security
- Granularity of access control mechanisms affects the balance between security and usability
- Fine-grained control provides better security but increases complexity
- Coarse-grained control simplifies management but may grant unnecessary permissions
Potential Vulnerabilities and Attacks
- can potentially bypass access control mechanisms
- Allow unauthorized information flow between processes or users
- Examples include timing channels and storage channels
- (TOCTOU) vulnerabilities arise from race conditions
- Can occur when there's a delay between checking permissions and accessing a resource
- Mitigated by using atomic operations and proper synchronization
- attacks exploit weaknesses in access control implementations
- Vertical privilege escalation (gaining higher-level permissions)
- Horizontal privilege escalation (accessing resources of other users at the same level)
Effectiveness and Management
- models generally provide stronger security guarantees
- More complex to manage and less flexible than discretionary models
- Effectiveness of access control policies depends on:
- Proper user authentication to ensure correct identity verification
- Secure storage of access control information to prevent tampering
- Regular auditing and monitoring of access control policies crucial for maintaining security
- Helps identify unauthorized access attempts and policy violations
- Allows for timely updates and adjustments to access control configurations
Key Terms to Review (22)
Access Control Lists: Access Control Lists (ACLs) are a set of rules that dictate what actions a user or system can perform on a resource within a computing environment. They are crucial for resource protection and access control, enabling administrators to specify who can read, write, or execute a file or directory. ACLs serve as a fundamental mechanism to enforce security policies by restricting access based on user identity and defined permissions.
Access Control Matrices: Access control matrices are a model used to define and manage permissions within computer systems, specifying which users or processes have access to which resources. This structure provides a clear way to visualize and enforce security policies by representing the rights of users in relation to different resources, ensuring that only authorized entities can access or manipulate specific data.
Accounting: In the context of resource protection and access control, accounting refers to the process of tracking and recording the resource usage of users and processes within a system. This information helps system administrators understand who is using which resources, monitor resource consumption, and ensure compliance with security policies. Effective accounting is essential for maintaining system integrity and helps identify unauthorized access or abuse of resources.
Attribute-based access control: Attribute-based access control (ABAC) is a method of managing permissions that grants or denies access to resources based on attributes associated with users, resources, and the environment. This approach provides fine-grained control over access decisions, making it adaptable to various contexts and scenarios by evaluating policies that incorporate these attributes.
Audit trails: Audit trails are records that provide a detailed log of all transactions, actions, or events related to a specific resource or process within a system. They are essential for tracking user activities and changes, ensuring accountability, and supporting compliance with security policies. This capability allows organizations to monitor access and detect unauthorized actions, thus playing a vital role in resource protection and access control.
Authentication: Authentication is the process of verifying the identity of a user or system, ensuring that the entities requesting access are who they claim to be. It plays a crucial role in security by enabling systems to differentiate between authorized users and potential threats, forming the first line of defense in resource protection, access control, and secure communication in various environments. Authentication methods can include passwords, biometric data, and multi-factor techniques, all aimed at safeguarding sensitive information across different applications and networks.
Authorization: Authorization is the process of granting or denying specific permissions to users, systems, or processes regarding access to resources. It ensures that only those who are permitted can perform certain actions, protecting sensitive data and maintaining system integrity. Authorization is crucial for resource protection, managing access in distributed environments, and implementing various access control mechanisms effectively.
Capability lists: Capability lists are a method of access control that specify which resources a process can access and what operations it can perform on those resources. They provide a way to associate permissions directly with the entities that own the resources, promoting fine-grained access control. This system is useful in managing security in operating systems by ensuring that only authorized processes can interact with specific resources.
Capability-based systems: Capability-based systems are a type of access control model that uses capabilities as the means to grant users the ability to access specific resources. In this model, capabilities are unforgeable tokens that convey both the rights and the specific object they can manipulate, making it easier to manage permissions without needing a centralized authority. This system enhances resource protection and access control by ensuring that only authorized users can perform certain actions on objects.
Covert Channels: Covert channels are methods that allow information to be transferred in a way that violates the system's security policy, often by exploiting unintended paths. These channels can occur through shared resources or even by manipulating existing communications to convey secret messages without detection. Understanding covert channels is critical for ensuring robust resource protection and access control mechanisms, as they can lead to unauthorized data leaks and breaches.
Discretionary Access Control: Discretionary Access Control (DAC) is a type of access control method that allows resource owners to make decisions about who is allowed to access specific resources. Under DAC, users can grant or revoke access permissions at their discretion, making it flexible but also potentially less secure. This model is significant in understanding how resources are protected and accessed, as well as the mechanisms used to enforce these controls.
File permissions: File permissions are a set of rules that determine who can access or modify a file in an operating system. They play a crucial role in resource protection, allowing the operating system to enforce security policies by controlling access to files based on user roles and privileges. By defining read, write, and execute permissions for different users and groups, file permissions help ensure data integrity and confidentiality.
Least Privilege Principle: The least privilege principle is a security concept that stipulates that users and programs should only have the minimum levels of access necessary to perform their functions. This principle aims to reduce the risk of unauthorized access to resources and potential damage, thereby enhancing overall security. By limiting permissions, systems can minimize vulnerabilities and potential attack surfaces, making it harder for malicious actors to exploit weaknesses.
Mandatory Access Control: Mandatory Access Control (MAC) is a security model that restricts access to resources based on fixed policies established by a central authority. In this model, users cannot alter permissions or access levels of resources, which helps maintain a higher level of security and ensures that sensitive information is adequately protected from unauthorized access. This concept ties closely into the evolution of operating systems, resource protection, access control mechanisms, and secure operating system design principles.
Privilege Escalation: Privilege escalation is a security exploit that allows an attacker to gain elevated access to resources that are normally protected from the user. This can involve moving from a lower level of permission to a higher one, allowing unauthorized users to access sensitive data or execute critical operations. Understanding this concept is crucial as it connects to resource protection mechanisms, the identification of security threats, and the principles behind designing secure operating systems.
Reference Monitor: A reference monitor is a conceptual framework used in operating systems to enforce access control policies by mediating all access requests between subjects (users or processes) and objects (files, devices, etc.). It ensures that all access attempts are checked against predefined security policies before granting or denying access. The reference monitor is essential for resource protection as it provides a mechanism for validating permissions and preventing unauthorized actions.
Role-based access control: Role-based access control (RBAC) is a method of restricting system access to authorized users based on their roles within an organization. This approach allows for efficient resource protection and access control by assigning permissions to specific roles rather than individual users. RBAC simplifies the management of user privileges and enhances security by ensuring that users can only access information and resources necessary for their roles.
Security logs: Security logs are records that capture events and activities related to the security of a system, including access attempts, changes to user permissions, and other security-related events. These logs are essential for monitoring, auditing, and analyzing system activities to detect unauthorized access or anomalies in user behavior, thus playing a vital role in resource protection and access control.
Separation of Privilege: Separation of privilege is a security principle that requires multiple conditions to be met before granting access to critical resources or performing sensitive operations. This concept minimizes the risk of unauthorized access by distributing permissions among different entities, ensuring that no single entity has complete control over a critical function. By doing this, systems enhance their resilience against threats and vulnerabilities.
Setuid/setgid: setuid (set user ID) and setgid (set group ID) are Unix/Linux access control features that allow users to execute a file with the permissions of the file owner or group, rather than their own. These special permission bits enhance security and resource protection by enabling controlled privilege escalation for specific programs, often used to perform tasks that require elevated permissions without granting those permissions to the user directly.
Sticky bit: The sticky bit is a permission setting in Unix-like operating systems that allows only the owner of a file or directory to delete or rename it, regardless of the permissions of other users. This feature enhances resource protection and access control by ensuring that important files in shared directories are not accidentally or intentionally removed by users who do not own them.
Time-of-check to time-of-use: Time-of-check to time-of-use (TOCTOU) refers to a race condition that occurs in computing when there is a time gap between checking a condition and using the result of that check. This can lead to security vulnerabilities, especially when access control mechanisms are involved, as it allows an attacker to change the state of the system between these two moments, potentially gaining unauthorized access to resources or data.