Transcript Database Security

DATABASE SECURITY
AND PRIVACY
Some slides were taken from
463.5.1 Database Access Control Tutorial, Lars Olson, UIUC CS463, Computer Security
Database Security
 Protect Sensitive Data from
 Unauthorized disclosure
 Unauthorized modification
 Denial of service attacks
Protection of Data Confidentiality
Access control – which data users can
access
 Information flow control – what users can
do with the accessed data

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
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
Protection Object





Database
Relation
Record
Attribute
Element
Advantages vs. disadvantages
of supporting
different granularity levels
Access Control Policies
Discretionary Access Control (DAC)
 Mandatory Access Control (MAC)
 Role-Based Access Control (RBAC)

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
DAC by Grant and Revoke
GRANT SELECT ON Employee
TO Black
WITH GRANT OPTION
?
Black
GRANT SELECT ON Employee
TO Red
Red
Brown revokes grant
given to Black
?
Brown (owner)
GRANT UPDATE(Salary) ON
Employee TO White
Brown does not want
Red to access the
Employee relation
White
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
Quick SQL Review
 Creating tables:
create table table_name (
column1 type1,
column2 type2,
...
);
 Deleting tables:
drop table table_name;
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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)
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Quick SQL Review
 Querying tables:
select column1, column2 from table_name;
or
select * from table_name;
 Conditions:
select columns from table_name
where condition;
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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;
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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, ...);
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Quick SQL Review
 Creating functions:
create [or replace] function
function_name (parameters)
return return_type as
[declare_local_variables]
begin
...
end;
/
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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
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Example Application
 Alice owns a database table of company
employees:
name varchar(50),
ssn int,
salary int,
email varchar(50)
 Some information (ssn, salary) should be
confidential, others can be viewed by any
employee.
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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,email) on employee to
carol;
 not implemented in PostgreSQL (see next slide)
 not implemented for select in Oracle
 implemented in MySQL
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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
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View-Based Access Control
 Alternative method to grant Carol access to
name and email columns:
create view employee_public as select
name,email from employee;
grant select on employee_public to
carol;
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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 e-mail
addresses:
grant update(email) on employee_Carol to
carol;
 (Or create yet another new view…)
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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;
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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?
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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.
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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
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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
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Cascading Revocations





grant(Alice,Bob)
grant(Alice,Carol)
grant(Carol,David)
grant(Bob,Carol)
revoke(Alice,Carol)
•
•
•
•
•
Alice
Carol
grant(Alice,Bob)
grant(Alice,Carol)
grant(Carol,David)
grant(Bob,Carol)
revoke(Alice,Carol)
?
David
Bob
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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
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 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
 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.)
 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.
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
RBAC
Individuals
Roles
Role 1
Role 2
Role 3
Users change frequently, Roles don’t
Resources
Server 1
Server 2
Server 3
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
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!
MAC
Individuals
Resources
Server 1
“Top Secret”
Server 2
“Secret”
Server 3
“Classified”
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!
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)
Multilevel Relation
Example
SSN
(SSN) Course
(Course) Grade
(Grade)
111-22-3333 S
CSCE 786
S
A
TS
444-55-6666 S
CSCE 567
S
C
TS
Top-secret user sees all data
Secret user sees Secret-View:
SSN
(SSN) Course
(Course) Grade
(Grade)
111-22-3333 S
CSCE 786
S
null
S
444-55-6666 S
CSCE 567
S
null
S
CSCE 790 - Farkas
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