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psalm/docs/security_analysis/custom_taint_sources.md
Oliver Hader ae54b72dba
Update documentation for taints and global configuration (#5098)
* [DOCS] Extend documentation on global variables configuration

* [DOCS] Synchronize meaning of @psalm-taint-source input with source code

* [DOCS] Add documentation for conditional @psalm-taint-escape

* [DOCS] Add documentation for @psalm-taint-unescape
2021-01-29 11:47:35 +01:00

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# Custom Taint Sources
You can define your own taint sources with an annotation or a plugin.
## Taint source annotation
You can use the annotation `@psalm-taint-source <taint-type>` to indicate a function or method that provides user input.
In the below example the `input` taint type is specified as a standin for input taints as defined in [Psalm\Type\TaintKindGroup](https://github.com/vimeo/psalm/blob/master/src/Psalm/Type/TaintKindGroup.php).
```php
/**
* @psalm-taint-source input
*/
function getQueryParam(string $name) : string {}
```
## Custom taint plugin
For example this plugin treats all variables named `$bad_data` as taint sources.
```php
<?php
namespace Some\Ns;
use PhpParser;
use Psalm\CodeLocation;
use Psalm\Context;
use Psalm\FileManipulation;
use Psalm\Plugin\EventHandler\AfterExpressionAnalysisInterface;
use Psalm\Plugin\EventHandler\Event\AfterExpressionAnalysisEvent;
use Psalm\Type\TaintKindGroup;
class BadSqlTainter implements AfterExpressionAnalysisInterface
{
/**
* Called after an expression has been checked
*
* @param PhpParser\Node\Expr $expr
* @param Context $context
* @param FileManipulation[] $file_replacements
*
* @return void
*/
public static function afterExpressionAnalysis(AfterExpressionAnalysisEvent $event): ?bool {
$expr = $event->getExpr();
$statements_source = $event->getStatementsSource();
$codebase = $event->getCodebase();
if ($expr instanceof PhpParser\Node\Expr\Variable
&& $expr->name === 'bad_data'
) {
$expr_type = $statements_source->getNodeTypeProvider()->getType($expr);
// should be a globally unique id
// you can use its line number/start offset
$expr_identifier = '$bad_data'
. '-' . $statements_source->getFileName()
. ':' . $expr->getAttribute('startFilePos');
if ($expr_type) {
$codebase->addTaintSource(
$expr_type,
$expr_identifier,
TaintKindGroup::ALL_INPUT,
new CodeLocation($statements_source, $expr)
);
}
}
}
}
```