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Add a security_barrier option for views.

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When a view is marked as a security barrier, it will not be pulled up
into the containing query, and no quals will be pushed down into it,
so that no function or operator chosen by the user can be applied to
rows not exposed by the view.  Views not configured with this
option cannot provide robust row-level security, but will perform far
better.

Patch by KaiGai Kohei; original problem report by Heikki Linnakangas
(in October 2009!).  Review (in earlier versions) by Noah Misch and
others.  Design advice by Tom Lane and myself.  Further review and
cleanup by me.
This commit is contained in:
Robert Haas
2011-12-22 16:15:57 -05:00
parent f90dd28062
commit 0e4611c023
22 changed files with 300 additions and 35 deletions
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20
doc/src/sgml/ref/alter_view.sgml
View File

@ -26,6 +26,8 @@ ALTER VIEW <replaceable class="parameter">name</replaceable> ALTER [ COLUMN ] <r
ALTER VIEW <replaceable class="parameter">name</replaceable> OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
ALTER VIEW <replaceable class="parameter">name</replaceable> RENAME TO <replaceable class="parameter">new_name</replaceable>
ALTER VIEW <replaceable class="parameter">name</replaceable> SET SCHEMA <replaceable class="parameter">new_schema</replaceable>
ALTER VIEW <replaceable class="parameter">name</replaceable> SET ( <replaceable class="parameter">view_option_name</replaceable> [= <replaceable class="parameter">view_option_value</replaceable>] [, ... ] )
ALTER VIEW <replaceable class="parameter">name</replaceable> RESET ( <replaceable class="parameter">view_option_name</replaceable> [, ... ] )
</synopsis>
</refsynopsisdiv>
@ -102,6 +104,24 @@ ALTER VIEW <replaceable class="parameter">name</replaceable> SET SCHEMA <replace
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">view_option_name</replaceable></term>
<listitem>
<para>
The name of a view option to be set or reset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">view_option_name</replaceable></term>
<listitem>
<para>
The new value for a view option.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>

13
doc/src/sgml/ref/create_view.sgml
View File

@ -22,6 +22,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW <replaceable class="PARAMETER">name</replaceable> [ ( <replaceable class="PARAMETER">column_name</replaceable> [, ...] ) ]
[ WITH ( <replaceable class="PARAMETER">view_option_name</replaceable> [= <replaceable class="PARAMETER">view_option_value</replaceable>] [, ... ] ) ]
AS <replaceable class="PARAMETER">query</replaceable>
</synopsis>
</refsynopsisdiv>
@ -98,6 +99,18 @@ CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW <replaceable class="PARAMETER">n
</listitem>
</varlistentry>
<varlistentry>
<term><literal>WITH ( <replaceable class="PARAMETER">view_option_name</replaceable> [= <replaceable class="PARAMETER">view_option_value</replaceable>] [, ... ] )</literal></term>
<listitem>
<para>
This clause specifies optional parameters for a view; currently, the
only suppored parameter name is <literal>security_barrier</literal>,
which should be enabled when a view is intended to provide row-level
security. See <xref linkend="rules-privileges"> for full details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">query</replaceable></term>
<listitem>

39
doc/src/sgml/rules.sgml
View File

@ -1822,8 +1822,9 @@ GRANT SELECT ON phone_number TO secretary;
<para>
Note that while views can be used to hide the contents of certain
columns using the technique shown above, they cannot be used to reliably
conceal the data in unseen rows. For example, the following view is
insecure:
conceal the data in unseen rows unless the
<literal>security_barrier</literal> flag has been set. For example,
the following view is insecure:
<programlisting>
CREATE VIEW phone_number AS
SELECT person, phone FROM phone_data WHERE phone NOT LIKE '412%';
@ -1870,6 +1871,40 @@ SELECT * FROM phone_number WHERE tricky(person, phone);
which references <literal>shoelace_log</> is an unqualified
<literal>INSERT</>. This might not be true in more complex scenarios.
</para>
<para>
When it is necessary for a view to provide row-level security, the
<literal>security_barrier</literal> attribute should be applied to
the view. This prevents maliciously-chosen functions and operators from
being invoked on rows until afterthe view has done its work. For
example, if the view shown above had been created like this, it would
be secure:
<programlisting>
CREATE VIEW phone_number WITH (security_barrier) AS
SELECT person, phone FROM phone_data WHERE phone NOT LIKE '412%';
</programlisting>
Views created with the <literal>security_barrier</literal> may perform
far worse than views created without this option. In general, there is
no way to avoid this: the fastest possible plan must be rejected
if it may compromise security. For this reason, this option is not
enabled by default.
</para>
<para>
It is important to understand that even a view created with the
<literal>security_barrier</literal> option is intended to be secure only
in the limited sense that the contents of the invisible tuples will not
passed to possibly-insecure functions. The user may well have other means
of making inferences about the unseen data; for example, they can see the
query plan using <command>EXPLAIN</command>, or measure the runtime of
queries against the view. A malicious attacker might be able to infer
something about the amount of unseen data, or even gain some information
about the data distribution or most common values (since these things may
affect the runtime of the plan; or even, since they are also reflected in
the optimizer statistics, the choice of plan). If these types of "covert
channel" attacks are of concern, it is probably unwise to grant any access
to the data at all.
</para>
</sect1>
<sect1 id="rules-status">