Command.php

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<?php
namespace MediaWiki\Shell;

use Exception;
use MediaWiki\ProcOpenError;
use MediaWiki\ShellDisabledError;
use Profiler;
use Psr\Log\LoggerAwareTrait;
use Psr\Log\NullLogger;
use Wikimedia\AtEase\AtEase;

class Command {
    use LoggerAwareTrait;

    protected $command = '';

    private $limits = [
        // seconds
        'time' => 180,
        // seconds
        'walltime' => 180,
        // KB
        'memory' => 307200,
        // KB
        'filesize' => 102400,
    ];

    private $env = [];

    private $method;

    private $inputString;

    private $doIncludeStderr = false;

    private $doLogStderr = false;

    private $everExecuted = false;

    private $cgroup = false;

    protected $restrictions = 0;

    public function __construct() {
        if ( Shell::isDisabled() ) {
            throw new ShellDisabledError();
        }

        $this->setLogger( new NullLogger() );
    }

    public function __destruct() {
        if ( !$this->everExecuted ) {
            $context = [ 'command' => $this->command ];
            $message = __CLASS__ . " was instantiated, but execute() was never called.";
            if ( $this->method ) {
                $message .= ' Calling method: {method}.';
                $context['method'] = $this->method;
            }
            $message .= ' Command: {command}';
            $this->logger->warning( $message, $context );
        }
    }

    public function params( ...$args ): Command {
        if ( count( $args ) === 1 && is_array( reset( $args ) ) ) {
            // If only one argument has been passed, and that argument is an array,
            // treat it as a list of arguments
            $args = reset( $args );
        }
        $this->command = trim( $this->command . ' ' . Shell::escape( $args ) );

        return $this;
    }

    public function unsafeParams( ...$args ): Command {
        if ( count( $args ) === 1 && is_array( reset( $args ) ) ) {
            // If only one argument has been passed, and that argument is an array,
            // treat it as a list of arguments
            $args = reset( $args );
        }
        $args = array_filter( $args,
            function ( $value ) {
                return $value !== null;
            }
        );
        $this->command = trim( $this->command . ' ' . implode( ' ', $args ) );

        return $this;
    }

    public function limits( array $limits ): Command {
        if ( !isset( $limits['walltime'] ) && isset( $limits['time'] ) ) {
            // Emulate the behavior of old wfShellExec() where walltime fell back on time
            // if the latter was overridden and the former wasn't
            $limits['walltime'] = $limits['time'];
        }
        $this->limits = $limits + $this->limits;

        return $this;
    }

    public function environment( array $env ): Command {
        $this->env = $env;

        return $this;
    }

    public function profileMethod( $method ): Command {
        $this->method = $method;

        return $this;
    }

    public function input( $inputString ): Command {
        $this->inputString = is_null( $inputString ) ? null : (string)$inputString;

        return $this;
    }

    public function includeStderr( $yesno = true ): Command {
        $this->doIncludeStderr = $yesno;

        return $this;
    }

    public function logStderr( $yesno = true ): Command {
        $this->doLogStderr = $yesno;

        return $this;
    }

    public function cgroup( $cgroup ): Command {
        $this->cgroup = $cgroup;

        return $this;
    }

    public function restrict( $restrictions ): Command {
        $this->restrictions |= $restrictions;

        return $this;
    }

    protected function hasRestriction( $restriction ) {
        return ( $this->restrictions & $restriction ) === $restriction;
    }

    public function whitelistPaths( array $paths ): Command {
        // Default implementation is a no-op
        return $this;
    }

    protected function buildFinalCommand( $command ) {
        $envcmd = '';
        foreach ( $this->env as $k => $v ) {
            if ( wfIsWindows() ) {
                /* Surrounding a set in quotes (method used by wfEscapeShellArg) makes the quotes themselves
                 * appear in the environment variable, so we must use carat escaping as documented in
                 * https://technet.microsoft.com/en-us/library/cc723564.aspx
                 * Note however that the quote isn't listed there, but is needed, and the parentheses
                 * are listed there but doesn't appear to need it.
                 */
                $envcmd .= "set $k=" . preg_replace( '/([&|()<>^"])/', '^\\1', $v ) . '&& ';
            } else {
                /* Assume this is a POSIX shell, thus required to accept variable assignments before the command
                 * http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_09_01
                 */
                $envcmd .= "$k=" . escapeshellarg( $v ) . ' ';
            }
        }

        $useLogPipe = false;
        $cmd = $envcmd . trim( $command );

        if ( is_executable( '/bin/bash' ) ) {
            $time = intval( $this->limits['time'] );
            $wallTime = intval( $this->limits['walltime'] );
            $mem = intval( $this->limits['memory'] );
            $filesize = intval( $this->limits['filesize'] );

            if ( $time > 0 || $mem > 0 || $filesize > 0 || $wallTime > 0 ) {
                $cmd = '/bin/bash ' . escapeshellarg( __DIR__ . '/limit.sh' ) . ' ' .
                    escapeshellarg( $cmd ) . ' ' .
                    escapeshellarg(
                        "MW_INCLUDE_STDERR=" . ( $this->doIncludeStderr ? '1' : '' ) . ';' .
                        "MW_CPU_LIMIT=$time; " .
                        'MW_CGROUP=' . escapeshellarg( $this->cgroup ) . '; ' .
                        "MW_MEM_LIMIT=$mem; " .
                        "MW_FILE_SIZE_LIMIT=$filesize; " .
                        "MW_WALL_CLOCK_LIMIT=$wallTime; " .
                        "MW_USE_LOG_PIPE=yes"
                    );
                $useLogPipe = true;
            }
        }
        if ( !$useLogPipe && $this->doIncludeStderr ) {
            $cmd .= ' 2>&1';
        }

        return [ $cmd, $useLogPipe ];
    }

    public function execute() {
        $this->everExecuted = true;

        $profileMethod = $this->method ?: wfGetCaller();

        list( $cmd, $useLogPipe ) = $this->buildFinalCommand( $this->command );

        $this->logger->debug( __METHOD__ . ": $cmd" );

        // Don't try to execute commands that exceed Linux's MAX_ARG_STRLEN.
        // Other platforms may be more accomodating, but we don't want to be
        // accomodating, because very long commands probably include user
        // input. See T129506.
        if ( strlen( $cmd ) > SHELL_MAX_ARG_STRLEN ) {
            throw new Exception( __METHOD__ .
                '(): total length of $cmd must not exceed SHELL_MAX_ARG_STRLEN' );
        }

        $desc = [
            0 => $this->inputString === null ? [ 'file', 'php://stdin', 'r' ] : [ 'pipe', 'r' ],
            1 => [ 'pipe', 'w' ],
            2 => [ 'pipe', 'w' ],
        ];
        if ( $useLogPipe ) {
            $desc[3] = [ 'pipe', 'w' ];
        }
        $pipes = null;
        $scoped = Profiler::instance()->scopedProfileIn( __FUNCTION__ . '-' . $profileMethod );
        $proc = proc_open( $cmd, $desc, $pipes );
        if ( !$proc ) {
            $this->logger->error( "proc_open() failed: {command}", [ 'command' => $cmd ] );
            throw new ProcOpenError();
        }

        $buffers = [
            0 => $this->inputString, // input
            1 => '', // stdout
            2 => null, // stderr
            3 => '', // log
        ];
        $emptyArray = [];
        $status = false;
        $logMsg = false;

        /* According to the documentation, it is possible for stream_select()
         * to fail due to EINTR. I haven't managed to induce this in testing
         * despite sending various signals. If it did happen, the error
         * message would take the form:
         *
         * stream_select(): unable to select [4]: Interrupted system call (max_fd=5)
         *
         * where [4] is the value of the macro EINTR and "Interrupted system
         * call" is string which according to the Linux manual is "possibly"
         * localised according to LC_MESSAGES.
         */
        $eintr = defined( 'SOCKET_EINTR' ) ? SOCKET_EINTR : 4;
        $eintrMessage = "stream_select(): unable to select [$eintr]";

        /* The select(2) system call only guarantees a "sufficiently small write"
         * can be made without blocking. And on Linux the read might block too
         * in certain cases, although I don't know if any of them can occur here.
         * Regardless, set all the pipes to non-blocking to avoid T184171.
         */
        foreach ( $pipes as $pipe ) {
            stream_set_blocking( $pipe, false );
        }

        $running = true;
        $timeout = null;
        $numReadyPipes = 0;

        while ( $pipes && ( $running === true || $numReadyPipes !== 0 ) ) {
            if ( $running ) {
                $status = proc_get_status( $proc );
                // If the process has terminated, switch to nonblocking selects
                // for getting any data still waiting to be read.
                if ( !$status['running'] ) {
                    $running = false;
                    $timeout = 0;
                }
            }

            // clear get_last_error without actually raising an error
            // from https://www.php.net/manual/en/function.error-get-last.php#113518
            // TODO replace with clear_last_error when requirements are bumped to PHP7
            set_error_handler( function () {
            }, 0 );
            AtEase::suppressWarnings();
            trigger_error( '' );
            AtEase::restoreWarnings();
            restore_error_handler();

            $readPipes = array_filter( $pipes, function ( $fd ) use ( $desc ) {
                return $desc[$fd][0] === 'pipe' && $desc[$fd][1] === 'r';
            }, ARRAY_FILTER_USE_KEY );
            $writePipes = array_filter( $pipes, function ( $fd ) use ( $desc ) {
                return $desc[$fd][0] === 'pipe' && $desc[$fd][1] === 'w';
            }, ARRAY_FILTER_USE_KEY );
            // stream_select parameter names are from the POV of us being able to do the operation;
            // proc_open desriptor types are from the POV of the process doing it.
            // So $writePipes is passed as the $read parameter and $readPipes as $write.
            AtEase::suppressWarnings();
            $numReadyPipes = stream_select( $writePipes, $readPipes, $emptyArray, $timeout );
            AtEase::restoreWarnings();
            if ( $numReadyPipes === false ) {
                $error = error_get_last();
                if ( strncmp( $error['message'], $eintrMessage, strlen( $eintrMessage ) ) == 0 ) {
                    continue;
                } else {
                    trigger_error( $error['message'], E_USER_WARNING );
                    $logMsg = $error['message'];
                    break;
                }
            }
            foreach ( $writePipes + $readPipes as $fd => $pipe ) {
                // True if a pipe is unblocked for us to write into, false if for reading from
                $isWrite = array_key_exists( $fd, $readPipes );

                if ( $isWrite ) {
                    // Don't bother writing if the buffer is empty
                    if ( $buffers[$fd] === '' ) {
                        fclose( $pipes[$fd] );
                        unset( $pipes[$fd] );
                        continue;
                    }
                    $res = fwrite( $pipe, $buffers[$fd], 65536 );
                } else {
                    $res = fread( $pipe, 65536 );
                }

                if ( $res === false ) {
                    $logMsg = 'Error ' . ( $isWrite ? 'writing to' : 'reading from' ) . ' pipe';
                    break 2;
                }

                if ( $res === '' || $res === 0 ) {
                    // End of file?
                    if ( feof( $pipe ) ) {
                        fclose( $pipes[$fd] );
                        unset( $pipes[$fd] );
                    }
                } elseif ( $isWrite ) {
                    $buffers[$fd] = (string)substr( $buffers[$fd], $res );
                    if ( $buffers[$fd] === '' ) {
                        fclose( $pipes[$fd] );
                        unset( $pipes[$fd] );
                    }
                } else {
                    $buffers[$fd] .= $res;
                    if ( $fd === 3 && strpos( $res, "\n" ) !== false ) {
                        // For the log FD, every line is a separate log entry.
                        $lines = explode( "\n", $buffers[3] );
                        $buffers[3] = array_pop( $lines );
                        foreach ( $lines as $line ) {
                            $this->logger->info( $line );
                        }
                    }
                }
            }
        }

        foreach ( $pipes as $pipe ) {
            fclose( $pipe );
        }

        // Use the status previously collected if possible, since proc_get_status()
        // just calls waitpid() which will not return anything useful the second time.
        if ( $running ) {
            $status = proc_get_status( $proc );
        }

        if ( $logMsg !== false ) {
            // Read/select error
            $retval = -1;
            proc_close( $proc );
        } elseif ( $status['signaled'] ) {
            $logMsg = "Exited with signal {$status['termsig']}";
            $retval = 128 + $status['termsig'];
            proc_close( $proc );
        } else {
            if ( $status['running'] ) {
                $retval = proc_close( $proc );
            } else {
                $retval = $status['exitcode'];
                proc_close( $proc );
            }
            if ( $retval == 127 ) {
                $logMsg = "Possibly missing executable file";
            } elseif ( $retval >= 129 && $retval <= 192 ) {
                $logMsg = "Probably exited with signal " . ( $retval - 128 );
            }
        }

        if ( $logMsg !== false ) {
            $this->logger->warning( "$logMsg: {command}", [ 'command' => $cmd ] );
        }

        if ( $buffers[2] && $this->doLogStderr ) {
            $this->logger->error( "Error running {command}: {error}", [
                'command' => $cmd,
                'error' => $buffers[2],
                'exitcode' => $retval,
                'exception' => new Exception( 'Shell error' ),
            ] );
        }

        return new Result( $retval, $buffers[1], $buffers[2] );
    }

    public function __toString() {
        return "#Command: {$this->command}";
    }
}