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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>5.8. Row Security Policies</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="ddl-priv.html" title="5.7. Privileges" /><link rel="next" href="ddl-schemas.html" title="5.9. Schemas" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">5.8. Row Security Policies</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ddl-priv.html" title="5.7. Privileges">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ddl.html" title="Chapter 5. Data Definition">Up</a></td><th width="60%" align="center">Chapter 5. Data Definition</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ddl-schemas.html" title="5.9. Schemas">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="DDL-ROWSECURITY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">5.8. Row Security Policies</h2></div></div></div><a id="id-1.5.4.10.2" class="indexterm"></a><a id="id-1.5.4.10.3" class="indexterm"></a><p>
   In addition to the SQL-standard <a class="link" href="ddl-priv.html" title="5.7. Privileges">privilege
   system</a> available through <a class="xref" href="sql-grant.html" title="GRANT"><span class="refentrytitle">GRANT</span></a>,
   tables can have <em class="firstterm">row security policies</em> that restrict,
   on a per-user basis, which rows can be returned by normal queries
   or inserted, updated, or deleted by data modification commands.
   This feature is also known as <em class="firstterm">Row-Level Security</em>.
   By default, tables do not have any policies, so that if a user has
   access privileges to a table according to the SQL privilege system,
   all rows within it are equally available for querying or updating.
  </p><p>
   When row security is enabled on a table (with
   <a class="link" href="sql-altertable.html" title="ALTER TABLE">ALTER TABLE ... ENABLE ROW LEVEL
   SECURITY</a>), all normal access to the table for selecting rows or
   modifying rows must be allowed by a row security policy.  (However, the
   table's owner is typically not subject to row security policies.)  If no
   policy exists for the table, a default-deny policy is used, meaning that
   no rows are visible or can be modified.  Operations that apply to the
   whole table, such as <code class="command">TRUNCATE</code> and <code class="literal">REFERENCES</code>,
   are not subject to row security.
  </p><p>
   Row security policies can be specific to commands, or to roles, or to
   both.  A policy can be specified to apply to <code class="literal">ALL</code>
   commands, or to <code class="literal">SELECT</code>, <code class="literal">INSERT</code>, <code class="literal">UPDATE</code>,
   or <code class="literal">DELETE</code>.  Multiple roles can be assigned to a given
   policy, and normal role membership and inheritance rules apply.
  </p><p>
   To specify which rows are visible or modifiable according to a policy,
   an expression is required that returns a Boolean result.  This
   expression will be evaluated for each row prior to any conditions or
   functions coming from the user's query.  (The only exceptions to this
   rule are <code class="literal">leakproof</code> functions, which are guaranteed to
   not leak information; the optimizer may choose to apply such functions
   ahead of the row-security check.)  Rows for which the expression does
   not return <code class="literal">true</code> will not be processed.  Separate expressions
   may be specified to provide independent control over the rows which are
   visible and the rows which are allowed to be modified.  Policy
   expressions are run as part of the query and with the privileges of the
   user running the query, although security-definer functions can be used
   to access data not available to the calling user.
  </p><p>
   Superusers and roles with the <code class="literal">BYPASSRLS</code> attribute always
   bypass the row security system when accessing a table.  Table owners
   normally bypass row security as well, though a table owner can choose to
   be subject to row security with <a class="link" href="sql-altertable.html" title="ALTER TABLE">ALTER
   TABLE ... FORCE ROW LEVEL SECURITY</a>.
  </p><p>
   Enabling and disabling row security, as well as adding policies to a
   table, is always the privilege of the table owner only.
  </p><p>
   Policies are created using the <a class="xref" href="sql-createpolicy.html" title="CREATE POLICY"><span class="refentrytitle">CREATE POLICY</span></a>
   command, altered using the <a class="xref" href="sql-alterpolicy.html" title="ALTER POLICY"><span class="refentrytitle">ALTER POLICY</span></a> command,
   and dropped using the <a class="xref" href="sql-droppolicy.html" title="DROP POLICY"><span class="refentrytitle">DROP POLICY</span></a> command.  To
   enable and disable row security for a given table, use the
   <a class="xref" href="sql-altertable.html" title="ALTER TABLE"><span class="refentrytitle">ALTER TABLE</span></a> command.
  </p><p>
   Each policy has a name and multiple policies can be defined for a
   table.  As policies are table-specific, each policy for a table must
   have a unique name.  Different tables may have policies with the
   same name.
  </p><p>
   When multiple policies apply to a given query, they are combined using
   either <code class="literal">OR</code> (for permissive policies, which are the
   default) or using <code class="literal">AND</code> (for restrictive policies).
   This is similar to the rule that a given role has the privileges
   of all roles that they are a member of.  Permissive vs. restrictive
   policies are discussed further below.
  </p><p>
   As a simple example, here is how to create a policy on
   the <code class="literal">account</code> relation to allow only members of
   the <code class="literal">managers</code> role to access rows, and only rows of their
   accounts:
  </p><pre class="programlisting">
CREATE TABLE accounts (manager text, company text, contact_email text);

ALTER TABLE accounts ENABLE ROW LEVEL SECURITY;

CREATE POLICY account_managers ON accounts TO managers
    USING (manager = current_user);
</pre><p>
   The policy above implicitly provides a <code class="literal">WITH CHECK</code>
   clause identical to its <code class="literal">USING</code> clause, so that the
   constraint applies both to rows selected by a command (so a manager
   cannot <code class="command">SELECT</code>, <code class="command">UPDATE</code>,
   or <code class="command">DELETE</code> existing rows belonging to a different
   manager) and to rows modified by a command (so rows belonging to a
   different manager cannot be created via <code class="command">INSERT</code>
   or <code class="command">UPDATE</code>).
  </p><p>
   If no role is specified, or the special user name
   <code class="literal">PUBLIC</code> is used, then the policy applies to all
   users on the system.  To allow all users to access only their own row in
   a <code class="literal">users</code> table, a simple policy can be used:
  </p><pre class="programlisting">
CREATE POLICY user_policy ON users
    USING (user_name = current_user);
</pre><p>
   This works similarly to the previous example.
  </p><p>
   To use a different policy for rows that are being added to the table
   compared to those rows that are visible, multiple policies can be
   combined.  This pair of policies would allow all users to view all rows
   in the <code class="literal">users</code> table, but only modify their own:
  </p><pre class="programlisting">
CREATE POLICY user_sel_policy ON users
    FOR SELECT
    USING (true);
CREATE POLICY user_mod_policy ON users
    USING (user_name = current_user);
</pre><p>
   In a <code class="command">SELECT</code> command, these two policies are combined
   using <code class="literal">OR</code>, with the net effect being that all rows
   can be selected.  In other command types, only the second policy applies,
   so that the effects are the same as before.
  </p><p>
   Row security can also be disabled with the <code class="command">ALTER TABLE</code>
   command.  Disabling row security does not remove any policies that are
   defined on the table; they are simply ignored.  Then all rows in the
   table are visible and modifiable, subject to the standard SQL privileges
   system.
  </p><p>
   Below is a larger example of how this feature can be used in production
   environments.  The table <code class="literal">passwd</code> emulates a Unix password
   file:
  </p><pre class="programlisting">
-- Simple passwd-file based example
CREATE TABLE passwd (
  user_name             text UNIQUE NOT NULL,
  pwhash                text,
  uid                   int  PRIMARY KEY,
  gid                   int  NOT NULL,
  real_name             text NOT NULL,
  home_phone            text,
  extra_info            text,
  home_dir              text NOT NULL,
  shell                 text NOT NULL
);

CREATE ROLE admin;  -- Administrator
CREATE ROLE bob;    -- Normal user
CREATE ROLE alice;  -- Normal user

-- Populate the table
INSERT INTO passwd VALUES
  ('admin','xxx',0,0,'Admin','111-222-3333',null,'/root','/bin/dash');
INSERT INTO passwd VALUES
  ('bob','xxx',1,1,'Bob','123-456-7890',null,'/home/bob','/bin/zsh');
INSERT INTO passwd VALUES
  ('alice','xxx',2,1,'Alice','098-765-4321',null,'/home/alice','/bin/zsh');

-- Be sure to enable row level security on the table
ALTER TABLE passwd ENABLE ROW LEVEL SECURITY;

-- Create policies
-- Administrator can see all rows and add any rows
CREATE POLICY admin_all ON passwd TO admin USING (true) WITH CHECK (true);
-- Normal users can view all rows
CREATE POLICY all_view ON passwd FOR SELECT USING (true);
-- Normal users can update their own records, but
-- limit which shells a normal user is allowed to set
CREATE POLICY user_mod ON passwd FOR UPDATE
  USING (current_user = user_name)
  WITH CHECK (
    current_user = user_name AND
    shell IN ('/bin/bash','/bin/sh','/bin/dash','/bin/zsh','/bin/tcsh')
  );

-- Allow admin all normal rights
GRANT SELECT, INSERT, UPDATE, DELETE ON passwd TO admin;
-- Users only get select access on public columns
GRANT SELECT
  (user_name, uid, gid, real_name, home_phone, extra_info, home_dir, shell)
  ON passwd TO public;
-- Allow users to update certain columns
GRANT UPDATE
  (pwhash, real_name, home_phone, extra_info, shell)
  ON passwd TO public;
</pre><p>
   As with any security settings, it's important to test and ensure that
   the system is behaving as expected.  Using the example above, this
   demonstrates that the permission system is working properly.
  </p><pre class="programlisting">
-- admin can view all rows and fields
postgres=&gt; set role admin;
SET
postgres=&gt; table passwd;
 user_name | pwhash | uid | gid | real_name |  home_phone  | extra_info | home_dir    |   shell
-----------+--------+-----+-----+-----------+--------------+------------+-------------+-----------
 admin     | xxx    |   0 |   0 | Admin     | 111-222-3333 |            | /root       | /bin/dash
 bob       | xxx    |   1 |   1 | Bob       | 123-456-7890 |            | /home/bob   | /bin/zsh
 alice     | xxx    |   2 |   1 | Alice     | 098-765-4321 |            | /home/alice | /bin/zsh
(3 rows)

-- Test what Alice is able to do
postgres=&gt; set role alice;
SET
postgres=&gt; table passwd;
ERROR:  permission denied for relation passwd
postgres=&gt; select user_name,real_name,home_phone,extra_info,home_dir,shell from passwd;
 user_name | real_name |  home_phone  | extra_info | home_dir    |   shell
-----------+-----------+--------------+------------+-------------+-----------
 admin     | Admin     | 111-222-3333 |            | /root       | /bin/dash
 bob       | Bob       | 123-456-7890 |            | /home/bob   | /bin/zsh
 alice     | Alice     | 098-765-4321 |            | /home/alice | /bin/zsh
(3 rows)

postgres=&gt; update passwd set user_name = 'joe';
ERROR:  permission denied for relation passwd
-- Alice is allowed to change her own real_name, but no others
postgres=&gt; update passwd set real_name = 'Alice Doe';
UPDATE 1
postgres=&gt; update passwd set real_name = 'John Doe' where user_name = 'admin';
UPDATE 0
postgres=&gt; update passwd set shell = '/bin/xx';
ERROR:  new row violates WITH CHECK OPTION for "passwd"
postgres=&gt; delete from passwd;
ERROR:  permission denied for relation passwd
postgres=&gt; insert into passwd (user_name) values ('xxx');
ERROR:  permission denied for relation passwd
-- Alice can change her own password; RLS silently prevents updating other rows
postgres=&gt; update passwd set pwhash = 'abc';
UPDATE 1
</pre><p>
   All of the policies constructed thus far have been permissive policies,
   meaning that when multiple policies are applied they are combined using
   the <span class="quote">“<span class="quote">OR</span>”</span> Boolean operator.  While permissive policies can be constructed
   to only allow access to rows in the intended cases, it can be simpler to
   combine permissive policies with restrictive policies (which the records
   must pass and which are combined using the <span class="quote">“<span class="quote">AND</span>”</span> Boolean operator).
   Building on the example above, we add a restrictive policy to require
   the administrator to be connected over a local Unix socket to access the
   records of the <code class="literal">passwd</code> table:
  </p><pre class="programlisting">
CREATE POLICY admin_local_only ON passwd AS RESTRICTIVE TO admin
    USING (pg_catalog.inet_client_addr() IS NULL);
</pre><p>
   We can then see that an administrator connecting over a network will not
   see any records, due to the restrictive policy:
  </p><pre class="programlisting">
=&gt; SELECT current_user;
 current_user 
--------------
 admin
(1 row)

=&gt; select inet_client_addr();
 inet_client_addr 
------------------
 127.0.0.1
(1 row)

=&gt; SELECT current_user;
 current_user 
--------------
 admin
(1 row)

=&gt; TABLE passwd;
 user_name | pwhash | uid | gid | real_name | home_phone | extra_info | home_dir | shell
-----------+--------+-----+-----+-----------+------------+------------+----------+-------
(0 rows)

=&gt; UPDATE passwd set pwhash = NULL;
UPDATE 0
</pre><p>
   Referential integrity checks, such as unique or primary key constraints
   and foreign key references, always bypass row security to ensure that
   data integrity is maintained.  Care must be taken when developing
   schemas and row level policies to avoid <span class="quote">“<span class="quote">covert channel</span>”</span> leaks of
   information through such referential integrity checks.
  </p><p>
   In some contexts it is important to be sure that row security is
   not being applied.  For example, when taking a backup, it could be
   disastrous if row security silently caused some rows to be omitted
   from the backup.  In such a situation, you can set the
   <a class="xref" href="runtime-config-client.html#GUC-ROW-SECURITY">row_security</a> configuration parameter
   to <code class="literal">off</code>.  This does not in itself bypass row security;
   what it does is throw an error if any query's results would get filtered
   by a policy.  The reason for the error can then be investigated and
   fixed.
  </p><p>
   In the examples above, the policy expressions consider only the current
   values in the row to be accessed or updated.  This is the simplest and
   best-performing case; when possible, it's best to design row security
   applications to work this way.  If it is necessary to consult other rows
   or other tables to make a policy decision, that can be accomplished using
   sub-<code class="command">SELECT</code>s, or functions that contain <code class="command">SELECT</code>s,
   in the policy expressions.  Be aware however that such accesses can
   create race conditions that could allow information leakage if care is
   not taken.  As an example, consider the following table design:
  </p><pre class="programlisting">
-- definition of privilege groups
CREATE TABLE groups (group_id int PRIMARY KEY,
                     group_name text NOT NULL);

INSERT INTO groups VALUES
  (1, 'low'),
  (2, 'medium'),
  (5, 'high');

GRANT ALL ON groups TO alice;  -- alice is the administrator
GRANT SELECT ON groups TO public;

-- definition of users' privilege levels
CREATE TABLE users (user_name text PRIMARY KEY,
                    group_id int NOT NULL REFERENCES groups);

INSERT INTO users VALUES
  ('alice', 5),
  ('bob', 2),
  ('mallory', 2);

GRANT ALL ON users TO alice;
GRANT SELECT ON users TO public;

-- table holding the information to be protected
CREATE TABLE information (info text,
                          group_id int NOT NULL REFERENCES groups);

INSERT INTO information VALUES
  ('barely secret', 1),
  ('slightly secret', 2),
  ('very secret', 5);

ALTER TABLE information ENABLE ROW LEVEL SECURITY;

-- a row should be visible to/updatable by users whose security group_id is
-- greater than or equal to the row's group_id
CREATE POLICY fp_s ON information FOR SELECT
  USING (group_id &lt;= (SELECT group_id FROM users WHERE user_name = current_user));
CREATE POLICY fp_u ON information FOR UPDATE
  USING (group_id &lt;= (SELECT group_id FROM users WHERE user_name = current_user));

-- we rely only on RLS to protect the information table
GRANT ALL ON information TO public;
</pre><p>
   Now suppose that <code class="literal">alice</code> wishes to change the <span class="quote">“<span class="quote">slightly
   secret</span>”</span> information, but decides that <code class="literal">mallory</code> should not
   be trusted with the new content of that row, so she does:
  </p><pre class="programlisting">
BEGIN;
UPDATE users SET group_id = 1 WHERE user_name = 'mallory';
UPDATE information SET info = 'secret from mallory' WHERE group_id = 2;
COMMIT;
</pre><p>
   That looks safe; there is no window wherein <code class="literal">mallory</code> should be
   able to see the <span class="quote">“<span class="quote">secret from mallory</span>”</span> string.  However, there is
   a race condition here.  If <code class="literal">mallory</code> is concurrently doing,
   say,
</p><pre class="programlisting">
SELECT * FROM information WHERE group_id = 2 FOR UPDATE;
</pre><p>
   and her transaction is in <code class="literal">READ COMMITTED</code> mode, it is possible
   for her to see <span class="quote">“<span class="quote">secret from mallory</span>”</span>.  That happens if her
   transaction reaches the <code class="structname">information</code> row just
   after <code class="literal">alice</code>'s does.  It blocks waiting
   for <code class="literal">alice</code>'s transaction to commit, then fetches the updated
   row contents thanks to the <code class="literal">FOR UPDATE</code> clause.  However, it
   does <span class="emphasis"><em>not</em></span> fetch an updated row for the
   implicit <code class="command">SELECT</code> from <code class="structname">users</code>, because that
   sub-<code class="command">SELECT</code> did not have <code class="literal">FOR UPDATE</code>; instead
   the <code class="structname">users</code> row is read with the snapshot taken at the start
   of the query.  Therefore, the policy expression tests the old value
   of <code class="literal">mallory</code>'s privilege level and allows her to see the
   updated row.
  </p><p>
   There are several ways around this problem.  One simple answer is to use
   <code class="literal">SELECT ... FOR SHARE</code> in sub-<code class="command">SELECT</code>s in row
   security policies.  However, that requires granting <code class="literal">UPDATE</code>
   privilege on the referenced table (here <code class="structname">users</code>) to the
   affected users, which might be undesirable.  (But another row security
   policy could be applied to prevent them from actually exercising that
   privilege; or the sub-<code class="command">SELECT</code> could be embedded into a security
   definer function.)  Also, heavy concurrent use of row share locks on the
   referenced table could pose a performance problem, especially if updates
   of it are frequent.  Another solution, practical if updates of the
   referenced table are infrequent, is to take an exclusive lock on the
   referenced table when updating it, so that no concurrent transactions
   could be examining old row values.  Or one could just wait for all
   concurrent transactions to end after committing an update of the
   referenced table and before making changes that rely on the new security
   situation.
  </p><p>
   For additional details see <a class="xref" href="sql-createpolicy.html" title="CREATE POLICY"><span class="refentrytitle">CREATE POLICY</span></a>
   and <a class="xref" href="sql-altertable.html" title="ALTER TABLE"><span class="refentrytitle">ALTER TABLE</span></a>.
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