DATABASE SECURITY AND PRIVACY. Some slides were taken from Database Access Control Tutorial, Lars Olson, UIUC CS463, Computer Security

Transcription

1 DATABASE SECURITY AND PRIVACY Some slides were taken from Database Access Control Tutorial, Lars Olson, UIUC CS463, Computer Security

2 Database Security Protect Sensitive Data from Unauthorized disclosure Unauthorized modification Denial of service attacks

3 Protection of Data Confidentiality Access control which data users can access Information flow control what users can do with the accessed data

4 Access Control Subject: active entity that requests access to an object - e.g., user or program Object: passive entity accessed by a subject - e.g., record, relation, file Access right (privileges): how a subject is allowed to access an object - e.g., subject s can read object o

5 Access Control Ensures that all direct accesses to object are authorized Protects against accidental and malicious threats by regulating the read, write and execution of data and programs

6 Protection Object Database Relation Record Attribute Element Advantages vs. disadvantages of supporting different granularity levels

7 Access Control Policies Discretionary Access Control (DAC) Mandatory Access Control (MAC) Role-Based Access Control (RBAC)

8 Discretionary Access Control (DAC) For each subject access right to the objects are defined (subject, object, +/- access mode) (Black, Employee-relation, read) User based Grant and Revoke Problems: - Propagation of access rights - Revocation of propagated access rights

9 DAC by Grant and Revoke GRANT SELECT ON Employee TO Black WITH GRANT OPTION? Brown revokes grant given to Black Brown (owner) GRANT UPDATE(Salary) ON Employee TO White Black GRANT SELECT ON Employee TO Red Red? Brown does not want Red to access the Employee relation White

10 DAC Restricts access to objects based solely on the identity of users who are trying to access them. Individuals Resources Server 1 Server 2 Server 3 Application Access List Name Access Tom Yes John No Cindy Yes

11 Quick SQL Review Creating tables: create table table_name ( column1 type1, column2 type2,... ); Deleting tables: drop table table_name; 11

12 Quick SQL Review Types: int float date char(size) Always delimited by single quote (apostrophe) Use two single quotes to represent the apostrophe character varchar(size) (varchar2 in Oracle) text (long in Oracle) 12

13 Quick SQL Review Querying tables: select column1, column2 from table_name; or select * from table_name; Conditions: select columns from table_name where condition; 13

14 Quick SQL Review Inserting new rows: insert into table_name values (value1, value2); or insert into table_name set column1=value1, column2=value2,...; Updating rows: update table_name set column1=value1 where condition; 14

15 Quick SQL Review Deleting rows: delete from table_name where condition; Set values in conditions: select * from table_name where column in (select_statement); or select * from table_name where column in (value1, value2,...); 15

16 Quick SQL Review Creating functions: create [or replace] function function_name (parameters) return return_type as [declare_local_variables] begin... end; / 16

17 SQL grant Syntax grant privilege_list on resource to user_list; Privileges include select, insert, etc. Resource may be a table, a database, a function, etc. User list may be individual users, or may be a user group Griffiths Wade 76 17

18 Example Application Alice owns a database table of company employees: name varchar(50), ssn int, salary int, varchar(50) Some information (ssn, salary) should be confidential, others can be viewed by any employee. 18

19 Simple Access Control Rules Suppose Bob needs access to the whole table (but doesn t need to make changes): grant select on employee to bob; Suppose Carol is another employee, who should only access public information: grant select(name, ) on employee to carol; not implemented in PostgreSQL (see next slide) not implemented for select in Oracle implemented in MySQL 19

20 Creating Views Careful with definitions! A subset of the database to which a user has access, or: A virtual table created as a shortcut query of other tables View syntax: create view view_name as query_definition; Querying views is nearly identical to querying regular tables 20

21 View-Based Access Control Alternative method to grant Carol access to name and columns: create view employee_public as select name, from employee; grant select on employee_public to carol; 21

22 Row-Level Access Control Suppose we also allow employees to view their own ssn, salary: create view employee_carol as select * from employee where name='carol'; grant select on employee_carol to carol; And we allow them to update their addresses: grant update( ) on employee_carol to carol; (Or create yet another new view ) 22

23 Delegating Policy Authority grant privilege_list on resource to user_list with grant option; Allows other users to grant privileges, including with grant option privileges Copy right from Access Control lecture Can grant subset privileges too Alice: grant select on table1 to bob with grant option; Bob: grant select(column1) on table1 to carol with grant option; 23

24 SQL revoke Syntax revoke privilege_list on resource from user_list; What happens when a user is granted access from two different sources, and one is revoked? What happens when a with grant option privilege is revoked? 24

25 Griffiths-Wade Model Sequences of grant / revoke operations When a privilege is revoked, the ACLs should be indistinguishable from a sequence in which the grant never occurred. 25

26 Grants from Multiple Sources grant(alice,bob) grant(alice,carol) grant(carol,bob) revoke(alice,bob) grant(alice,bob) grant(alice,carol) grant(carol,bob) revoke(alice,bob) Bob Alice Carol 26

27 Not as Easy as it Looks! grant(alice,bob) grant(bob,carol) grant(carol,bob) revoke(alice,bob) grant(alice,bob) grant(bob,carol) grant(carol,bob) revoke(alice,bob) Bob Alice Carol 27

28 Cascading Revocations grant(alice,bob) grant(alice,carol) grant(carol,david) grant(bob,carol) revoke(alice,carol) grant(alice,bob) grant(alice,carol) grant(carol,david) grant(bob,carol) revoke(alice,carol) Alice Carol? David Bob 28

29 Meanwhile, in the Real World... Account privileges get changed all the time We don t always want to redo everything Tedious Involves other users actions SQL revoke command has two optional arguments: cascade: undoes all dependent grant commands restrict: exits with failure if there exist dependent grants Ramakrishnan Gehrke 03 29

30 User1: creates Example_Table within Example_Schema. grants SELECT WITH GRANT OPTION on Example_Table to User2. User2 grants the SELECT WITH GRANT OPTION on Example_Table to User3 User3 grants SELECT on Example_Table to the Reviewer role. >REVOKE SELECT ON EXAMPLE_TABLE FROM USER2 CASCADE

31 User1: creates Example_Table within Example_Schema. grants SELECT WITH GRANT OPTION on Example_Table to User2. User2 grants the SELECT WITH GRANT OPTION on Example_Table to User3 User3 grants SELECT on Example_Table to the Reviewer role. >REVOKE SELECT ON EXAMPLE_TABLE FROM USER2 CASCADE When the superuser or User1 executes this statement, the SELECT privilege on Example_Table is revoked from User2, User3, and the Reviewer Role. (The GRANT privilege is also revoked from User2 and User3.)

32 User1: creates Example_Table within Example_Schema. grants SELECT WITH GRANT OPTION on Example_Table to User2. User2 grants the SELECT WITH GRANT OPTION on Example_Table to User3 User3 grants SELECT on Example_Table to the Reviewer role. >REVOKE SELECT ON EXAMPLE_TABLE FROM USER2 RESTRICT Since there is depending grants, the revoke fails.

33 RBAC (Role Based Access Control Roles permit common privileges for a class of users can be specified just once by creating a corresponding role Privileges can be granted to or revoked from roles Roles can be assigned to users, and even to other roles

34 RBAC Individuals Roles Resources Role 1 Server 1 Role 2 Server 2 Role 3 Server 3 Users change frequently, Roles don t

35 Mandatory Access Control (MAC) Security label - Top-Secret, Secret, Public Objects: security classification - File 1 is Secret, File 2 is Public Subjects: security clearances - Brown is cleared to Secret, Black is cleared to Public Dominance ( ) - Top-Secret Secret Public

36 MAC Access rights: defined by comparing the security classification of the requested objects with the security clearance of the subject If access control rules are satisfied, access is permitted Otherwise access is rejected Granularity of access rights!

37 MAC Individuals Resources Server 1 Top Secret Server 2 Secret Server 3 Classified

38 MAC Single security property: a subject S is allowed a read access to an object O only if label(s) dominates label(o) Star-property: a subject S is allowed a write access to an object O only if label(o) dominates label(s) No direct flow of information from high security objects to low security objects!

39 Multilevel Security Multilevel security users at different security level, see different versions of the database Problem: different versions need to be kept consistent and coherent without downward signaling channel (covert channel)

40 Multilevel Relation Example SSN (SSN) Course (Course) Grade (Grade) S CSCE 786 S A TS S CSCE 567 S C TS Top-secret user sees all data Secret user sees Secret-View: SSN (SSN) Course (Course) Grade (Grade) S CSCE 786 S null S S CSCE 567 S null S CSCE Farkas 41