qmachparser.cpp - mozsearch

// Copyright (C) 2016 Intel Corporation.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

// Qt-Security score:critical reason:data-parser

#include "qmachparser_p.h"

#include <qendian.h>

#include <optional>

#include <mach-o/loader.h>

#include <mach-o/fat.h>

QT_BEGIN_NAMESPACE

using namespace Qt::StringLiterals;

// Whether we include some extra validity checks

// (checks to ensure we don't read out-of-bounds are always included)

static constexpr bool IncludeValidityChecks = true;

#if defined(Q_PROCESSOR_X86_64)

#  define MACHO64

static const cpu_type_t my_cputype = CPU_TYPE_X86_64;

#elif defined(Q_PROCESSOR_X86_32)

static const cpu_type_t my_cputype = CPU_TYPE_X86;

#elif defined(Q_PROCESSOR_POWER_64)

#  define MACHO64

static const cpu_type_t my_cputype = CPU_TYPE_POWERPC64;

#elif defined(Q_PROCESSOR_POWER_32)

static const cpu_type_t my_cputype = CPU_TYPE_POWERPC;

#elif defined(Q_PROCESSOR_ARM_64)

#  define MACHO64

static const cpu_type_t my_cputype = CPU_TYPE_ARM64;

#elif defined(Q_PROCESSOR_ARM)

static const cpu_type_t my_cputype = CPU_TYPE_ARM;

#else

#  error "Unknown CPU type"

#endif

#ifdef MACHO64

#  undef MACHO64

typedef mach_header_64 my_mach_header;

typedef segment_command_64 my_segment_command;

typedef section_64 my_section;

static const uint32_t my_magic = MH_MAGIC_64;

#else

typedef mach_header my_mach_header;

typedef segment_command my_segment_command;

typedef section my_section;

static const uint32_t my_magic = MH_MAGIC;

#endif

Q_DECL_COLD_FUNCTION

static QLibraryScanResult notfound(const QString &reason, QString *errorString)

    *errorString = QLibrary::tr("'%1' is not a valid Mach-O binary (%2)")

            .arg(*errorString, reason.isEmpty() ? QLibrary::tr("file is corrupt") : reason);

    return {};

// Returns whether the binary is encrypted, or nullopt if the load-command table

// is malformed or extends past the end of the (mmapped) file.

static std::optional<bool> isEncrypted(const my_mach_header *header, ulong fdlen)

    auto commandCursor = uintptr_t(header) + sizeof(my_mach_header);

    // QMachOParser::parse() verifies that fdlen is large enough for at least

    // my_mach_header + load_command.

    ulong minsize = sizeof(my_mach_header);

    for (uint32_t i = 0; i < header->ncmds; ++i) {

        // We must be able to read the load command header (cmd + cmdsize).

        if (Q_UNLIKELY(fdlen - sizeof(load_command) < minsize))

            return std::nullopt;

        load_command *loadCommand = reinterpret_cast<load_command *>(commandCursor);

        const uint32_t cmdsize = loadCommand->cmdsize;

        // A load command must at least contain its own header

        if (Q_UNLIKELY(cmdsize < sizeof(load_command)))

            return std::nullopt;

        // cmdsize can't be trusted until validated against fdlen

        if (qAddOverflow(minsize, ulong(cmdsize), &minsize) || Q_UNLIKELY(minsize > fdlen))

            return std::nullopt;

        if (loadCommand->cmd == LC_ENCRYPTION_INFO || loadCommand->cmd == LC_ENCRYPTION_INFO_64) {

            // The layout of encryption_info_command and encryption_info_command_64 is the same

            // up until and including cryptid, so we can treat it as encryption_info_command.

            // Make sure the command is big enough to hold the field we read.

            if (Q_UNLIKELY(cmdsize < sizeof(encryption_info_command)))

                return std::nullopt;

            auto encryptionInfoCommand = reinterpret_cast<encryption_info_command*>(loadCommand);

            return encryptionInfoCommand->cryptid != 0;

        commandCursor += cmdsize;

    return false;

QLibraryScanResult  QMachOParser::parse(const char *m_s, ulong fdlen, QString *errorString)

    // The minimum size of a Mach-O binary we're interested in.

    // It must have a full Mach header, at least one segment and at least one

    // section. It's probably useless with just the "qtmetadata" section, but

    // it's valid nonetheless.

    // A fat binary must have this plus the fat header, of course.

    static const size_t MinFileSize = sizeof(my_mach_header) + sizeof(my_segment_command) + sizeof(my_section);

    static const size_t MinFatHeaderSize = sizeof(fat_header) + 2 * sizeof(fat_arch);

    if (Q_UNLIKELY(fdlen < MinFileSize))

        return notfound(QLibrary::tr("file too small"), errorString);

    // find out if this is a fat Mach-O binary first

    const my_mach_header *header = nullptr;

    const fat_header *fat = reinterpret_cast<const fat_header *>(m_s);

    if (fat->magic == qToBigEndian(FAT_MAGIC)) {

        // find our architecture in the binary

        const fat_arch *arch = reinterpret_cast<const fat_arch *>(fat + 1);

        if (Q_UNLIKELY(fdlen < MinFatHeaderSize)) {

            return notfound(QLibrary::tr("file too small"), errorString);

        int count = qFromBigEndian(fat->nfat_arch);

        if (Q_UNLIKELY(fdlen < sizeof(*fat) + sizeof(*arch) * count))

            return notfound(QString(), errorString);

        for (int i = 0; i < count; ++i) {

            if (arch[i].cputype == qToBigEndian(my_cputype)) {

                // ### should we check the CPU subtype? Maybe on ARM?

                uint32_t size = qFromBigEndian(arch[i].size);

                uint32_t offset = qFromBigEndian(arch[i].offset);

                if (Q_UNLIKELY(size > fdlen) || Q_UNLIKELY(offset > fdlen)

                        || Q_UNLIKELY(size + offset > fdlen) || Q_UNLIKELY(size < MinFileSize))

                    return notfound(QString(), errorString);

                header = reinterpret_cast<const my_mach_header *>(m_s + offset);

                fdlen = size;

                break;

        if (!header)

            return notfound(QLibrary::tr("no suitable architecture in fat binary"), errorString);

        // check the magic again

        if (Q_UNLIKELY(header->magic != my_magic))

            return notfound(QString(), errorString);

    } else {

        header = reinterpret_cast<const my_mach_header *>(m_s);

        fat = 0;

        // check magic

        if (header->magic != my_magic)

            return notfound(QLibrary::tr("invalid magic %1").arg(qFromBigEndian(header->magic),

                                                                 8, 16, '0'_L1),

                      errorString);

    // from this point on, everything is in host byte order

    // (re-)check the CPU type

    // ### should we check the CPU subtype? Maybe on ARM?

    if (header->cputype != my_cputype) {

        if (fat)

            return notfound(QString(), errorString);

        return notfound(QLibrary::tr("wrong architecture"), errorString);

    // check the file type

    if (Q_UNLIKELY(header->filetype != MH_BUNDLE && header->filetype != MH_DYLIB))

        return notfound(QLibrary::tr("not a dynamic library"), errorString);

    // find the __TEXT segment, "qtmetadata" section

    const my_segment_command *seg = reinterpret_cast<const my_segment_command *>(header + 1);

    ulong minsize = sizeof(*header);

    for (uint i = 0; i < header->ncmds; ++i,

         seg = reinterpret_cast<const my_segment_command *>(reinterpret_cast<const char *>(seg) + seg->cmdsize)) {

        // We're sure that the file size includes at least one load command

        // but we have to check anyway if we're past the first

        if (Q_UNLIKELY(fdlen < minsize + sizeof(load_command)))

            return notfound(QString(), errorString);

        // cmdsize can't be trusted until validated

        // so check it against fdlen anyway

        // (these are unsigned operations, with overflow behavior specified in the standard)

        minsize += seg->cmdsize;

        if (Q_UNLIKELY(fdlen < minsize) || Q_UNLIKELY(fdlen < seg->cmdsize))

            return notfound(QString(), errorString);

        const uint32_t MyLoadCommand = sizeof(void *) > 4 ? LC_SEGMENT_64 : LC_SEGMENT;

        if (seg->cmd != MyLoadCommand)

            continue;

        // is this the __TEXT segment?

        if (strcmp(seg->segname, "__TEXT") == 0) {

            const my_section *sect = reinterpret_cast<const my_section *>(seg + 1);

            for (uint j = 0; j < seg->nsects; ++j) {

                // is this the "qtmetadata" section?

                if (strcmp(sect[j].sectname, "qtmetadata") != 0)

                    continue;

                // found it!

                if (Q_UNLIKELY(fdlen < sect[j].offset) || Q_UNLIKELY(fdlen < sect[j].size)

                        || Q_UNLIKELY(fdlen < sect[j].offset + sect[j].size))

                    return notfound(QString(), errorString);

                if (sect[j].size < sizeof(QPluginMetaData::MagicHeader))

                    return notfound(QLibrary::tr(".qtmetadata section is too small"), errorString);

                const std::optional<bool> binaryIsEncrypted = isEncrypted(header, fdlen);

                if (Q_UNLIKELY(!binaryIsEncrypted))

                    return notfound(QLibrary::tr("corrupted encryption_info section"), errorString);

                qsizetype pos = reinterpret_cast<const char *>(header) - m_s + sect[j].offset;

                // We can not read the section data of encrypted libraries until they

                // have been dlopened(), so skip validity check if that's the case.

                if (IncludeValidityChecks && !*binaryIsEncrypted) {

                    QByteArrayView expectedMagic = QByteArrayView::fromArray(QPluginMetaData::MagicString);

                    QByteArrayView actualMagic = QByteArrayView(m_s + pos, expectedMagic.size());

                    if (expectedMagic != actualMagic)

                        return notfound(QLibrary::tr(".qtmetadata section has incorrect magic"), errorString);

                pos += sizeof(QPluginMetaData::MagicString);

                return { pos, qsizetype(sect[j].size - sizeof(QPluginMetaData::MagicString)), *binaryIsEncrypted };

        // other type of segment

        seg = reinterpret_cast<const my_segment_command *>(reinterpret_cast<const char *>(seg) + seg->cmdsize);

    // No .qtmetadata section was found

    *errorString = QLibrary::tr("'%1' is not a Qt plugin").arg(*errorString);

    return {};

QT_END_NAMESPACE

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