CREATE POLICY — define a new row level security policy for a table
CREATE POLICYname
ONtable_name
[ AS { PERMISSIVE | RESTRICTIVE } ] [ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ] [ TO {role_name
| PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ] [ USING (using_expression
) ] [ WITH CHECK (check_expression
) ]
The CREATE POLICY
command defines a new row-level
security policy for a table. Note that row-level security must be
enabled on the table (using ALTER TABLE ... ENABLE ROW LEVEL
SECURITY
) in order for created policies to be applied.
A policy grants the permission to select, insert, update, or delete rows
that match the relevant policy expression. Existing table rows are
checked against the expression specified in USING
,
while new rows that would be created via INSERT
or UPDATE
are checked against the expression specified
in WITH CHECK
. When a USING
expression returns true for a given row then that row is visible to the
user, while if false or null is returned then the row is not visible.
When a WITH CHECK
expression returns true for a row
then that row is inserted or updated, while if false or null is returned
then an error occurs.
For INSERT
and UPDATE
statements,
WITH CHECK
expressions are enforced after
BEFORE
triggers are fired, and before any actual data
modifications are made. Thus a BEFORE ROW
trigger may
modify the data to be inserted, affecting the result of the security
policy check. WITH CHECK
expressions are enforced
before any other constraints.
Policy names are per-table. Therefore, one policy name can be used for many different tables and have a definition for each table which is appropriate to that table.
Policies can be applied for specific commands or for specific roles. The default for newly created policies is that they apply for all commands and roles, unless otherwise specified. Multiple policies may apply to a single command; see below for more details. Table 272 summarizes how the different types of policy apply to specific commands.
For policies that can have both USING
and WITH CHECK
expressions (ALL
and UPDATE
), if no WITH CHECK
expression is defined, then the USING
expression will be
used both to determine which rows are visible (normal
USING
case) and which new rows will be allowed to be
added (WITH CHECK
case).
If row-level security is enabled for a table, but no applicable policies exist, a “default deny” policy is assumed, so that no rows will be visible or updatable.
name
The name of the policy to be created. This must be distinct from the name of any other policy for the table.
table_name
The name (optionally schema-qualified) of the table the policy applies to.
PERMISSIVE
Specify that the policy is to be created as a permissive policy. All permissive policies which are applicable to a given query will be combined together using the Boolean “OR” operator. By creating permissive policies, administrators can add to the set of records which can be accessed. Policies are permissive by default.
RESTRICTIVE
Specify that the policy is to be created as a restrictive policy. All restrictive policies which are applicable to a given query will be combined together using the Boolean “AND” operator. By creating restrictive policies, administrators can reduce the set of records which can be accessed as all restrictive policies must be passed for each record.
Note that there needs to be at least one permissive policy to grant access to records before restrictive policies can be usefully used to reduce that access. If only restrictive policies exist, then no records will be accessible. When a mix of permissive and restrictive policies are present, a record is only accessible if at least one of the permissive policies passes, in addition to all the restrictive policies.
command
The command to which the policy applies. Valid options are
ALL
, SELECT
,
INSERT
, UPDATE
,
and DELETE
.
ALL
is the default.
See below for specifics regarding how these are applied.
role_name
The role(s) to which the policy is to be applied. The default is
PUBLIC
, which will apply the policy to all roles.
using_expression
Any SQL conditional expression (returning
boolean
). The conditional expression cannot contain
any aggregate or window functions. This expression will be added
to queries that refer to the table if row level security is enabled.
Rows for which the expression returns true will be visible. Any
rows for which the expression returns false or null will not be
visible to the user (in a SELECT
), and will not be
available for modification (in an UPDATE
or DELETE
). Such rows are silently suppressed; no error
is reported.
check_expression
Any SQL conditional expression (returning
boolean
). The conditional expression cannot contain
any aggregate or window functions. This expression will be used in
INSERT
and UPDATE
queries against
the table if row level security is enabled. Only rows for which the
expression evaluates to true will be allowed. An error will be thrown
if the expression evaluates to false or null for any of the records
inserted or any of the records that result from the update. Note that
the check_expression
is
evaluated against the proposed new contents of the row, not the
original contents.
ALL
Using ALL
for a policy means that it will apply
to all commands, regardless of the type of command. If an
ALL
policy exists and more specific policies
exist, then both the ALL
policy and the more
specific policy (or policies) will be applied.
Additionally, ALL
policies will be applied to
both the selection side of a query and the modification side, using
the USING
expression for both cases if only
a USING
expression has been defined.
As an example, if an UPDATE
is issued, then the
ALL
policy will be applicable both to what the
UPDATE
will be able to select as rows to be
updated (applying the USING
expression),
and to the resulting updated rows, to check if they are permitted
to be added to the table (applying the WITH CHECK
expression, if defined, and the USING
expression
otherwise). If an INSERT
or UPDATE
command attempts to add rows to the
table that do not pass the ALL
policy's WITH CHECK
expression, the entire
command will be aborted.
SELECT
Using SELECT
for a policy means that it will apply
to SELECT
queries and whenever
SELECT
permissions are required on the relation the
policy is defined for. The result is that only those records from the
relation that pass the SELECT
policy will be
returned during a SELECT
query, and that queries
that require SELECT
permissions, such as
UPDATE
, will also only see those records
that are allowed by the SELECT
policy.
A SELECT
policy cannot have a WITH
CHECK
expression, as it only applies in cases where
records are being retrieved from the relation.
INSERT
Using INSERT
for a policy means that it will apply
to INSERT
commands. Rows being inserted that do
not pass this policy will result in a policy violation error, and the
entire INSERT
command will be aborted.
An INSERT
policy cannot have
a USING
expression, as it only applies in cases
where records are being added to the relation.
Note that INSERT
with ON CONFLICT DO
UPDATE
checks INSERT
policies'
WITH CHECK
expressions only for rows appended
to the relation by the INSERT
path.
UPDATE
Using UPDATE
for a policy means that it will apply
to UPDATE
, SELECT FOR UPDATE
and SELECT FOR SHARE
commands, as well as
auxiliary ON CONFLICT DO UPDATE
clauses of
INSERT
commands. Since UPDATE
involves pulling an existing record and replacing it with a new
modified record, UPDATE
policies accept both a USING
expression and
a WITH CHECK
expression.
The USING
expression determines which records
the UPDATE
command will see to operate against,
while the WITH CHECK
expression defines which
modified rows are allowed to be stored back into the relation.
Any rows whose updated values do not pass the
WITH CHECK
expression will cause an error, and the
entire command will be aborted. If only a USING
clause is specified, then that clause will be used for both
USING
and WITH CHECK
cases.
Typically an UPDATE
command also needs to read
data from columns in the relation being updated (e.g., in a
WHERE
clause or a RETURNING
clause, or in an expression on the right hand side of the
SET
clause). In this case,
SELECT
rights are also required on the relation
being updated, and the appropriate SELECT
or
ALL
policies will be applied in addition to
the UPDATE
policies. Thus the user must have
access to the row(s) being updated through a SELECT
or ALL
policy in addition to being granted
permission to update the row(s) via an UPDATE
or ALL
policy.
When an INSERT
command has an auxiliary
ON CONFLICT DO UPDATE
clause, if the
UPDATE
path is taken, the row to be updated is
first checked against the USING
expressions of
any UPDATE
policies, and then the new updated row
is checked against the WITH CHECK
expressions.
Note, however, that unlike a standalone UPDATE
command, if the existing row does not pass the
USING
expressions, an error will be thrown (the
UPDATE
path will never be silently
avoided).
DELETE
Using DELETE
for a policy means that it will apply
to DELETE
commands. Only rows that pass this
policy will be seen by a DELETE
command. There can
be rows that are visible through a SELECT
that are
not available for deletion, if they do not pass the
USING
expression for
the DELETE
policy.
In most cases a DELETE
command also needs to read
data from columns in the relation that it is deleting from (e.g.,
in a WHERE
clause or a
RETURNING
clause). In this case,
SELECT
rights are also required on the relation,
and the appropriate SELECT
or
ALL
policies will be applied in addition to
the DELETE
policies. Thus the user must have
access to the row(s) being deleted through a SELECT
or ALL
policy in addition to being granted
permission to delete the row(s) via a DELETE
or
ALL
policy.
A DELETE
policy cannot have a WITH
CHECK
expression, as it only applies in cases where
records are being deleted from the relation, so that there is no
new row to check.
Table 272. Policies Applied by Command Type
Command | SELECT/ALL policy | INSERT/ALL policy | UPDATE/ALL policy | DELETE/ALL policy | |
---|---|---|---|---|---|
USING expression | WITH CHECK expression | USING expression | WITH CHECK expression | USING expression | |
SELECT | Existing row | — | — | — | — |
SELECT FOR UPDATE/SHARE | Existing row | — | Existing row | — | — |
INSERT | — | New row | — | — | — |
INSERT ... RETURNING | New row [a] | New row | — | — | — |
UPDATE | Existing & new rows [a] | — | Existing row | New row | — |
DELETE | Existing row [a] | — | — | — | Existing row |
ON CONFLICT DO UPDATE | Existing & new rows | — | Existing row | New row | — |
[a]
If read access is required to the existing or new row (for example,
a |
When multiple policies of different command types apply to the same command
(for example, SELECT
and UPDATE
policies applied to an UPDATE
command), then the user
must have both types of permissions (for example, permission to select rows
from the relation as well as permission to update them). Thus the
expressions for one type of policy are combined with the expressions for
the other type of policy using the AND
operator.
When multiple policies of the same command type apply to the same command,
then there must be at least one PERMISSIVE
policy
granting access to the relation, and all of the
RESTRICTIVE
policies must pass. Thus all the
PERMISSIVE
policy expressions are combined using
OR
, all the RESTRICTIVE
policy
expressions are combined using AND
, and the results are
combined using AND
. If there are no
PERMISSIVE
policies, then access is denied.
Note that, for the purposes of combining multiple policies,
ALL
policies are treated as having the same type as
whichever other type of policy is being applied.
For example, in an UPDATE
command requiring both
SELECT
and UPDATE
permissions, if
there are multiple applicable policies of each type, they will be combined
as follows:
expression
from RESTRICTIVE SELECT/ALL policy 1 ANDexpression
from RESTRICTIVE SELECT/ALL policy 2 AND ... AND (expression
from PERMISSIVE SELECT/ALL policy 1 ORexpression
from PERMISSIVE SELECT/ALL policy 2 OR ... ) ANDexpression
from RESTRICTIVE UPDATE/ALL policy 1 ANDexpression
from RESTRICTIVE UPDATE/ALL policy 2 AND ... AND (expression
from PERMISSIVE UPDATE/ALL policy 1 ORexpression
from PERMISSIVE UPDATE/ALL policy 2 OR ... )
You must be the owner of a table to create or change policies for it.
While policies will be applied for explicit queries against tables in the database, they are not applied when the system is performing internal referential integrity checks or validating constraints. This means there are indirect ways to determine that a given value exists. An example of this is attempting to insert a duplicate value into a column that is a primary key or has a unique constraint. If the insert fails then the user can infer that the value already exists. (This example assumes that the user is permitted by policy to insert records which they are not allowed to see.) Another example is where a user is allowed to insert into a table which references another, otherwise hidden table. Existence can be determined by the user inserting values into the referencing table, where success would indicate that the value exists in the referenced table. These issues can be addressed by carefully crafting policies to prevent users from being able to insert, delete, or update records at all which might possibly indicate a value they are not otherwise able to see, or by using generated values (e.g., surrogate keys) instead of keys with external meanings.
Generally, the system will enforce filter conditions imposed using
security policies prior to qualifications that appear in user queries,
in order to prevent inadvertent exposure of the protected data to
user-defined functions which might not be trustworthy. However,
functions and operators marked by the system (or the system
administrator) as LEAKPROOF
may be evaluated before
policy expressions, as they are assumed to be trustworthy.
Since policy expressions are added to the user's query directly, they will be run with the rights of the user running the overall query. Therefore, users who are using a given policy must be able to access any tables or functions referenced in the expression or they will simply receive a permission denied error when attempting to query the table that has row-level security enabled. This does not change how views work, however. As with normal queries and views, permission checks and policies for the tables which are referenced by a view will use the view owner's rights and any policies which apply to the view owner.
Additional discussion and practical examples can be found in Section 5.8.
CREATE POLICY
is a LightDB
extension.