349 lines
14 KiB
Plaintext
349 lines
14 KiB
Plaintext
<!--
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doc/src/sgml/ref/create_policy.sgml
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PostgreSQL documentation
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-->
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<refentry id="SQL-CREATEPOLICY">
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<indexterm zone="sql-createpolicy">
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<primary>CREATE POLICY</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>CREATE POLICY</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE POLICY</refname>
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<refpurpose>define a new policy for a table</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table_name</replaceable>
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[ FOR { ALL | SELECT | INSERT | UPDATE | DELETE } ]
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[ TO { <replaceable class="parameter">role_name</replaceable> | PUBLIC | CURRENT_USER | SESSION_USER } [, ...] ]
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[ USING ( <replaceable class="parameter">using_expression</replaceable> ) ]
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[ WITH CHECK ( <replaceable class="parameter">check_expression</replaceable> ) ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>
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The <command>CREATE POLICY</command> command defines a new policy for a
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table. Note that row level security must also be enabled on the table using
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<command>ALTER TABLE</command> in order for created policies to be applied.
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</para>
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<para>
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A policy grants the ability to SELECT, INSERT, UPDATE, or DELETE rows
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which match the relevant policy expression. Existing table rows are
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checked against the expression specified via USING, while new rows that
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would be created via INSERT or UPDATE are checked against the expression
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specified via WITH CHECK. When a USING expression returns true for a given
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row then that row is visible to the user, while if a false or null is
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returned then the row is not visible. When a WITH CHECK expression
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returns true for a row then that row is added, while if a false or null is
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returned then an error occurs.
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</para>
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<para>
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Generally, the system will enforce filter conditions imposed using
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security policies prior to qualifications that appear in the query itself,
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in order to the prevent the inadvertent exposure of the protected data to
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user-defined functions which might not be trustworthy. However,
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functions and operators marked by the system (or the system
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administrator) as LEAKPROOF may be evaluated before policy
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expressions, as they are assumed to be trustworthy.
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</para>
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<para>
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For INSERT and UPDATE queries, WITH CHECK expressions are enforced after
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BEFORE triggers are fired, and before any data modifications are made.
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Thus a BEFORE ROW trigger may modify the data to be inserted, affecting
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the result of the security policy check. WITH CHECK expressions are
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enforced before any other constraints.
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</para>
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<para>
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Policy names are per-table, therefore one policy name can be used for many
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different tables and have a definition for each table which is appropriate to
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that table.
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</para>
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<para>
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Policies can be applied for specific commands or for specific roles. The
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default for newly created policies is that they apply for all commands and
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roles, unless otherwise specified. If multiple policies apply to a given
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query, they will be combined using OR. Further, for commands which can have
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both USING and WITH CHECK policies (ALL and UPDATE), if no WITH CHECK policy
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is defined then the USING policy will be used for both what rows are visible
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(normal USING case) and which rows will be allowed to be added (WITH CHECK
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case).
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</para>
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<para>
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Note that while policies will be applied for explicit queries against tables
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in the system, they are not applied when the system is performing internal
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referential integrity checks or validating constraints. This means there are
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indirect ways to determine that a given value exists. An example of this is
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attempting to insert a duplicate value into a column which is the primary key
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or has a unique constraint. If the insert fails then the user can infer that
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the value already exists (this example assumes that the user is permitted by
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policy to insert records which they are not allowed to see). Another example
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is where a user is allowed to insert into a table which references another,
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otherwise hidden table. Existence can be determined by the user inserting
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values into the referencing table, where success would indicate that the
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value exists in the referenced table. These issues can be addressed by
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carefully crafting policies which prevent users from being able to insert,
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delete, or update records at all which might possibly indicate a value they
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are not otherwise able to see, or by using generated values (e.g.: surrogate
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keys) instead.
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</para>
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<para>
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Regarding how policy expressions interact with the user: as the expressions
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are added to the user's query directly, they will be run with the rights of
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the user running the overall query. Therefore, users who are using a given
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policy must be able to access any tables or functions referenced in the
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expression or they will simply receive a permission denied error when
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attempting to query the RLS-enabled table. This does not change how views
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work, however. As with normal queries and views, permission checks and
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policies for the tables which are referenced by a view will use the view
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owner's rights and any policies which apply to the view owner.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><replaceable class="parameter">name</replaceable></term>
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<listitem>
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<para>
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The name of the policy to be created. This must be distinct from the
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name of any other policy for the table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">table_name</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of the table the
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policy applies to.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">command</replaceable></term>
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<listitem>
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<para>
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The command to which the policy applies. Valid options are
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<command>ALL</command>, <command>SELECT</command>,
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<command>INSERT</command>, <command>UPDATE</command>,
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and <command>DELETE</command>.
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<command>ALL</command> is the default.
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See below for specifics regarding how these are applied.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">role_name</replaceable></term>
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<listitem>
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<para>
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The roles to which the policy is to be applied. The default is
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<literal>PUBLIC</literal>, which will apply the policy to all roles.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">using_expression</replaceable></term>
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<listitem>
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<para>
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Any <acronym>SQL</acronym> conditional expression (returning
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<type>boolean</type>). The conditional expression cannot contain
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any aggregate or window functions. This expression will be added
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to queries that refer to the table if row level security is enabled
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and rows for which the expression returns true will be visible. Any
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rows for which the expression returns false or null will not be
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visible to the user.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">check_expression</replaceable></term>
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<listitem>
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<para>
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Any <acronym>SQL</acronym> conditional expression (returning
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<type>boolean</type>). The conditional expression cannot contain
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any aggregate or window functions. This expression will be used with
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<command>INSERT</command> and <command>UPDATE</command> queries against
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the table if row level security is enabled and only rows where the
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expression evaluates to true will be allowed. An error will be thrown
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if the expression evaluates to false or null for any of the records
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inserted or any of the records which result from the update.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Per-Command policies</title>
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<variablelist>
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<varlistentry id="SQL-CREATEPOLICY-ALL">
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<term><literal>ALL</></term>
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<listitem>
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<para>
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Using <literal>ALL</literal> for a policy means that it will apply
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to all commands, regardless of the type of command. If an
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<literal>ALL</literal> policy exists and more specific policies
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exist, then both the <literal>ALL</literal> policy and the more
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specific policy (or policies) will be combined using
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<literal>OR</literal>, as usual for overlapping policies.
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Additionally, <literal>ALL</literal> policies will be applied to
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both the selection side of a query and the modification side, using
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the USING policy for both if only a USING policy has been defined.
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As an example, if an <literal>UPDATE</literal> is issued, then the
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<literal>ALL</literal> policy will be applicable to both what the
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<literal>UPDATE</literal> will be able to select out as rows to be
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updated (with the USING expression being applied), and it will be
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applied to rows which result from the <literal>UPDATE</literal>
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statement, to check if they are permitted to be added to the table
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(using the WITH CHECK expression, if defined, and the USING expression
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otherwise). If an INSERT or UPDATE command attempts to add rows to
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the table which do not pass the <literal>ALL</literal> WITH CHECK
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expression, the entire command will be aborted. Note that if only a
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<literal>USING</literal> clause is specified then that clause will be
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used for both <literal>USING</literal> and
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<literal>WITH CHECK</literal> cases.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="SQL-CREATEPOLICY-SELECT">
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<term><literal>SELECT</></term>
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<listitem>
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<para>
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Using <literal>SELECT</literal> for a policy means that it will apply
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to <literal>SELECT</literal> commands. The result is that only those
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records from the relation which pass the <literal>SELECT</literal>
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policy will be returned, even if other records exist in the relation.
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The <literal>SELECT</literal> policy only accepts the USING expression
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as it only ever applies in cases where records are being retrieved from
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the relation.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="SQL-CREATEPOLICY-INSERT">
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<term><literal>INSERT</></term>
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<listitem>
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<para>
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Using <literal>INSERT</literal> for a policy means that it will apply
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to <literal>INSERT</literal> commands. Rows being inserted which do
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not pass this policy will result in a policy violation ERROR and the
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entire <literal>INSERT</literal> command will be aborted. The
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<literal>INSERT</literal> policy only accepts the WITH CHECK expression
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as it only ever applies in cases where records are being added to the
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relation.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="SQL-CREATEPOLICY-UPDATE">
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<term><literal>UPDATE</></term>
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<listitem>
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<para>
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Using <literal>UPDATE</literal> for a policy means that it will apply
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to <literal>UPDATE</literal> commands. As <literal>UPDATE</literal>
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involves pulling an existing record and then making changes to some
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portion (but possibly not all) of the record, the
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<literal>UPDATE</literal> policy accepts both a USING expression and
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a WITH CHECK expression. The USING expression will be used to
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determine which records the <literal>UPDATE</literal> command will
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see to operate against, while the <literal>WITH CHECK</literal>
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expression defines what rows are allowed to be added back into the
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relation (similar to the <literal>INSERT</literal> policy).
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Any rows whose resulting values do not pass the
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<literal>WITH CHECK</literal> expression will cause an ERROR and the
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entire command will be aborted. Note that if only a
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<literal>USING</literal> clause is specified then that clause will be
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used for both <literal>USING</literal> and
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<literal>WITH CHECK</literal> cases.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="SQL-CREATEPOLICY-DELETE">
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<term><literal>DELETE</></term>
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<listitem>
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<para>
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Using <literal>DELETE</literal> for a policy means that it will apply
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to <literal>DELETE</literal> commands. Only rows which pass this
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policy will be seen by a <literal>DELETE</literal> command. Rows may
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be visible through a <literal>SELECT</literal> which are not seen by a
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<literal>DELETE</literal>, as they do not pass the USING expression
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for the <literal>DELETE</literal>, and rows which are not visible
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through the <literal>SELECT</literal> policy may be deleted if they
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pass the <literal>DELETE</literal> USING policy. The
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<literal>DELETE</literal> policy only accepts the USING expression as
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it only ever applies in cases where records are being extracted from
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the relation for deletion.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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You must be the owner of a table to create or change policies for it.
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</para>
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<para>
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In order to maintain <firstterm>referential integrity</firstterm> between
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two related tables, policies are not applied when the system performs
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checks on foreign key constraints.
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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<command>CREATE POLICY</command> is a <productname>PostgreSQL</productname>
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extension.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterpolicy"></member>
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<member><xref linkend="sql-droppolicy"></member>
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</simplelist>
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</refsect1>
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</refentry>
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