194 lines
9.4 KiB
HTML
194 lines
9.4 KiB
HTML
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<!-- keywords: {authorizer callback} sqlite3_set_authorizer -->
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<a href="intro.html"><h2>SQLite C Interface</h2></a>
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<h2>Compile-Time Authorization Callbacks</h2>
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</div>
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<blockquote><pre>
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int sqlite3_set_authorizer(
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sqlite3*,
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int (*xAuth)(void*,int,const char*,const char*,const char*,const char*),
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void *pUserData
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);
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</pre></blockquote>
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<p>
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This routine registers an authorizer callback with a particular
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<a href="../c3ref/sqlite3.html">database connection</a>, supplied in the first argument.
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The authorizer callback is invoked as SQL statements are being compiled
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by <a href="../c3ref/prepare.html">sqlite3_prepare()</a> or its variants <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a>,
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<a href="../c3ref/prepare.html">sqlite3_prepare_v3()</a>, <a href="../c3ref/prepare.html">sqlite3_prepare16()</a>, <a href="../c3ref/prepare.html">sqlite3_prepare16_v2()</a>,
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and <a href="../c3ref/prepare.html">sqlite3_prepare16_v3()</a>. At various
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points during the compilation process, as logic is being created
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to perform various actions, the authorizer callback is invoked to
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see if those actions are allowed. The authorizer callback should
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return <a href="../rescode.html#ok">SQLITE_OK</a> to allow the action, <a href="../c3ref/c_deny.html">SQLITE_IGNORE</a> to disallow the
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specific action but allow the SQL statement to continue to be
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compiled, or <a href="../c3ref/c_deny.html">SQLITE_DENY</a> to cause the entire SQL statement to be
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rejected with an error. If the authorizer callback returns
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any value other than <a href="../c3ref/c_deny.html">SQLITE_IGNORE</a>, <a href="../rescode.html#ok">SQLITE_OK</a>, or <a href="../c3ref/c_deny.html">SQLITE_DENY</a>
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then the <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> or equivalent call that triggered
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the authorizer will fail with an error message.</p>
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<p>When the callback returns <a href="../rescode.html#ok">SQLITE_OK</a>, that means the operation
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requested is ok. When the callback returns <a href="../c3ref/c_deny.html">SQLITE_DENY</a>, the
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<a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> or equivalent call that triggered the
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authorizer will fail with an error message explaining that
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access is denied.</p>
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<p>The first parameter to the authorizer callback is a copy of the third
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parameter to the sqlite3_set_authorizer() interface. The second parameter
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to the callback is an integer <a href="../c3ref/c_alter_table.html">action code</a> that specifies
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the particular action to be authorized. The third through sixth parameters
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to the callback are either NULL pointers or zero-terminated strings
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that contain additional details about the action to be authorized.
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Applications must always be prepared to encounter a NULL pointer in any
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of the third through the sixth parameters of the authorization callback.</p>
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<p>If the action code is <a href="../c3ref/c_alter_table.html">SQLITE_READ</a>
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and the callback returns <a href="../c3ref/c_deny.html">SQLITE_IGNORE</a> then the
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<a href="../c3ref/stmt.html">prepared statement</a> statement is constructed to substitute
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a NULL value in place of the table column that would have
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been read if <a href="../rescode.html#ok">SQLITE_OK</a> had been returned. The <a href="../c3ref/c_deny.html">SQLITE_IGNORE</a>
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return can be used to deny an untrusted user access to individual
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columns of a table.
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When a table is referenced by a <a href="../lang_select.html">SELECT</a> but no column values are
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extracted from that table (for example in a query like
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"SELECT count(*) FROM tab") then the <a href="../c3ref/c_alter_table.html">SQLITE_READ</a> authorizer callback
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is invoked once for that table with a column name that is an empty string.
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If the action code is <a href="../c3ref/c_alter_table.html">SQLITE_DELETE</a> and the callback returns
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<a href="../c3ref/c_deny.html">SQLITE_IGNORE</a> then the <a href="../lang_delete.html">DELETE</a> operation proceeds but the
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<a href="../lang_delete.html#truncateopt">truncate optimization</a> is disabled and all rows are deleted individually.</p>
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<p>An authorizer is used when <a href="../c3ref/prepare.html">preparing</a>
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SQL statements from an untrusted source, to ensure that the SQL statements
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do not try to access data they are not allowed to see, or that they do not
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try to execute malicious statements that damage the database. For
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example, an application may allow a user to enter arbitrary
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SQL queries for evaluation by a database. But the application does
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not want the user to be able to make arbitrary changes to the
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database. An authorizer could then be put in place while the
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user-entered SQL is being <a href="../c3ref/prepare.html">prepared</a> that
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disallows everything except <a href="../lang_select.html">SELECT</a> statements.</p>
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<p>Applications that need to process SQL from untrusted sources
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might also consider lowering resource limits using <a href="../c3ref/limit.html">sqlite3_limit()</a>
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and limiting database size using the <a href="../pragma.html#pragma_max_page_count">max_page_count</a> <a href="../pragma.html#syntax">PRAGMA</a>
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in addition to using an authorizer.</p>
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<p>Only a single authorizer can be in place on a database connection
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at a time. Each call to sqlite3_set_authorizer overrides the
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previous call. Disable the authorizer by installing a NULL callback.
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The authorizer is disabled by default.</p>
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<p>The authorizer callback must not do anything that will modify
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the database connection that invoked the authorizer callback.
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Note that <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> and <a href="../c3ref/step.html">sqlite3_step()</a> both modify their
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database connections for the meaning of "modify" in this paragraph.</p>
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<p>When <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> is used to prepare a statement, the
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statement might be re-prepared during <a href="../c3ref/step.html">sqlite3_step()</a> due to a
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schema change. Hence, the application should ensure that the
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correct authorizer callback remains in place during the <a href="../c3ref/step.html">sqlite3_step()</a>.</p>
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<p>Note that the authorizer callback is invoked only during
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<a href="../c3ref/prepare.html">sqlite3_prepare()</a> or its variants. Authorization is not
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performed during statement evaluation in <a href="../c3ref/step.html">sqlite3_step()</a>, unless
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as stated in the previous paragraph, sqlite3_step() invokes
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sqlite3_prepare_v2() to reprepare a statement after a schema change.
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</p><p>See also lists of
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<a href="objlist.html">Objects</a>,
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<a href="constlist.html">Constants</a>, and
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<a href="funclist.html">Functions</a>.</p>
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