ApiCSPReport.php

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<?php
use MediaWiki\Json\FormatJson;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MainConfigNames;
use MediaWiki\Request\ContentSecurityPolicy;
use Psr\Log\LoggerInterface;
use Wikimedia\ParamValidator\ParamValidator;
 
class ApiCSPReport extends ApiBase {
 
    private LoggerInterface $log;
 
    private const MAX_POST_SIZE = 8192;
 
    public function execute() {
        $reportOnly = $this->getParameter( 'reportonly' );
        $logname = $reportOnly ? 'csp-report-only' : 'csp';
        $this->log = LoggerFactory::getInstance( $logname );
        $userAgent = $this->getRequest()->getHeader( 'user-agent' );
 
        $this->verifyPostBodyOk();
        $report = $this->getReport();
        $flags = $this->getFlags( $report, $userAgent );
 
        $warningText = $this->generateLogLine( $flags, $report );
        $this->logReport( $flags, $warningText, [
            // XXX Is it ok to put untrusted data into log??
            'csp-report' => $report,
            'method' => __METHOD__,
            'user_id' => $this->getUser()->getId() ?: 'logged-out',
            'user-agent' => $userAgent,
            'source' => $this->getParameter( 'source' ),
        ] );
        $this->getResult()->addValue( null, $this->getModuleName(), 'success' );
    }
 
    private function logReport( $flags, $logLine, $context ) {
        if ( in_array( 'false-positive', $flags ) ) {
            // These reports probably don't matter much
            $this->log->debug( $logLine, $context );
        } else {
            // Normal report.
            $this->log->warning( $logLine, $context );
        }
    }
 
    private function getFlags( $report, $userAgent ) {
        $reportOnly = $this->getParameter( 'reportonly' );
        $source = $this->getParameter( 'source' );
        $falsePositives = $this->getConfig()->get( MainConfigNames::CSPFalsePositiveUrls );
 
        $flags = [];
        if ( $source !== 'internal' ) {
            $flags[] = 'source=' . $source;
        }
        if ( $reportOnly ) {
            $flags[] = 'report-only';
        }
 
        if (
            (
                ContentSecurityPolicy::falsePositiveBrowser( $userAgent ) &&
                $report['blocked-uri'] === "self"
            ) ||
            (
                isset( $report['blocked-uri'] ) &&
                $this->matchUrlPattern( $report['blocked-uri'], $falsePositives )
            ) ||
            (
                isset( $report['source-file'] ) &&
                $this->matchUrlPattern( $report['source-file'], $falsePositives )
            )
        ) {
            // False positive due to:
            // https://bugzilla.mozilla.org/show_bug.cgi?id=1026520
 
            $flags[] = 'false-positive';
        }
        return $flags;
    }
 
    private function matchUrlPattern( $url, array $patterns ) {
        if ( isset( $patterns[ $url ] ) ) {
            return true;
        }
 
        $bits = wfParseUrl( $url );
        unset( $bits['user'], $bits['pass'], $bits['query'], $bits['fragment'] );
        $bits['path'] = '';
        $serverUrl = wfAssembleUrl( $bits );
        if ( isset( $patterns[$serverUrl] ) ) {
            // The origin of the url matches a pattern,
            // e.g. "https://example.org" matches "https://example.org/foo/b?a#r"
            return true;
        }
        foreach ( $patterns as $pattern => $val ) {
            // We only use this pattern if it ends in a slash, this prevents
            // "/foos" from matching "/foo", and "https://good.combo.bad" matching
            // "https://good.com".
            if ( str_ends_with( $pattern, '/' ) && str_starts_with( $url, $pattern ) ) {
                // The pattern starts with the same as the url
                // e.g. "https://example.org/foo/" matches "https://example.org/foo/b?a#r"
                return true;
            }
        }
 
        return false;
    }
 
    private function verifyPostBodyOk() {
        $req = $this->getRequest();
        $contentType = $req->getHeader( 'content-type' );
        if ( $contentType !== 'application/json'
            && $contentType !== 'application/csp-report'
        ) {
            $this->error( 'wrongformat', __METHOD__ );
        }
        if ( $req->getHeader( 'content-length' ) > self::MAX_POST_SIZE ) {
            $this->error( 'toobig', __METHOD__ );
        }
    }
 
    private function getReport() {
        $postBody = $this->getRequest()->getRawInput();
        if ( strlen( $postBody ) > self::MAX_POST_SIZE ) {
            // paranoia, already checked content-length earlier.
            $this->error( 'toobig', __METHOD__ );
        }
        $status = FormatJson::parse( $postBody, FormatJson::FORCE_ASSOC );
        if ( !$status->isGood() ) {
            $msg = $status->getErrors()[0]['message'];
            if ( $msg instanceof Message ) {
                $msg = $msg->getKey();
            }
            $this->error( $msg, __METHOD__ );
        }
 
        $report = $status->getValue();
 
        if ( !isset( $report['csp-report'] ) ) {
            $this->error( 'missingkey', __METHOD__ );
        }
        return $report['csp-report'];
    }
 
    private function generateLogLine( $flags, $report ) {
        $flagText = '';
        if ( $flags ) {
            $flagText = '[' . implode( ', ', $flags ) . ']';
        }
 
        $blockedOrigin = isset( $report['blocked-uri'] )
            ? $this->originFromUrl( $report['blocked-uri'] )
            : 'n/a';
        $page = $report['document-uri'] ?? 'n/a';
        $line = isset( $report['line-number'] )
            ? ':' . $report['line-number']
            : '';
        return $flagText .
            ' Received CSP report: <' . $blockedOrigin . '>' .
            ' blocked from being loaded on <' . $page . '>' . $line;
    }
 
    private function originFromUrl( $url ) {
        $bits = wfParseUrl( $url );
        unset( $bits['user'], $bits['pass'], $bits['query'], $bits['fragment'] );
        $bits['path'] = '';
        // e.g. "https://example.org" from "https://example.org/foo/b?a#r"
        return wfAssembleUrl( $bits );
    }
 
    private function error( $code, $method ) {
        $this->log->info( 'Error reading CSP report: ' . $code, [
            'method' => $method,
            'user-agent' => $this->getRequest()->getHeader( 'user-agent' )
        ] );
        // Return 400 on error for user agents to display, e.g. to the console.
        $this->dieWithError(
            [ 'apierror-csp-report', wfEscapeWikiText( $code ) ], 'cspreport-' . $code, [], 400
        );
    }
 
    public function getAllowedParams() {
        return [
            'reportonly' => [
                ParamValidator::PARAM_TYPE => 'boolean',
                ParamValidator::PARAM_DEFAULT => false
            ],
            'source' => [
                ParamValidator::PARAM_TYPE => 'string',
                ParamValidator::PARAM_DEFAULT => 'internal',
                ParamValidator::PARAM_REQUIRED => false
            ]
        ];
    }
 
    public function mustBePosted() {
        return true;
    }
 
    public function isInternal() {
        return true;
    }
 
    public function isReadMode() {
        return false;
    }
 
    public function shouldCheckMaxLag() {
        return false;
    }
}