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Commit 40a8223d authored by Yi-Yo Chiang's avatar Yi-Yo Chiang
Browse files

libfstab_fuzzer: fuzz TransformFstabForDsu() and skip mount logic 

These functions contain complex logic and parse user input. It shall be
valuable to fuzz these functions to prevent regression.

Bug: 254832225
Test: Build and run the fuzzer
Change-Id: I21099c3fc1c226f95a0f8f996bb751030e0c59bc
parent 9457a9ab

fs_mgr/fs_mgr_fstab.cpp

+14 −7
Original line number Original line Diff line number Diff line
@@ -754,10 +754,11 @@ bool ReadFstabFromDt(Fstab* fstab, bool verbose) { 
}

}





#ifdef NO_SKIP_MOUNT

#ifdef NO_SKIP_MOUNT

bool SkipMountingPartitions(Fstab*, bool) {

static constexpr bool kNoSkipMount = true;

    return true;

}

#else

#else

static constexpr bool kNoSkipMount = false;

#endif



// For GSI to skip mounting /product and /system_ext, until there are well-defined interfaces

// For GSI to skip mounting /product and /system_ext, until there are well-defined interfaces

// between them and /system. Otherwise, the GSI flashed on /system might not be able to work with

// between them and /system. Otherwise, the GSI flashed on /system might not be able to work with

// device-specific /product and /system_ext. skip_mount.cfg belongs to system_ext partition because

// device-specific /product and /system_ext. skip_mount.cfg belongs to system_ext partition because
@@ -765,17 +766,24 @@ bool SkipMountingPartitions(Fstab*, bool) { 
// /system/system_ext because GSI is a single system.img that includes the contents of system_ext

// /system/system_ext because GSI is a single system.img that includes the contents of system_ext

// partition and product partition under /system/system_ext and /system/product, respectively.

// partition and product partition under /system/system_ext and /system/product, respectively.

bool SkipMountingPartitions(Fstab* fstab, bool verbose) {

bool SkipMountingPartitions(Fstab* fstab, bool verbose) {

    if (kNoSkipMount) {

        return true;

    }



    static constexpr char kSkipMountConfig[] = "/system/system_ext/etc/init/config/skip_mount.cfg";

    static constexpr char kSkipMountConfig[] = "/system/system_ext/etc/init/config/skip_mount.cfg";





    std::string skip_config;

    std::string skip_mount_config;

    auto save_errno = errno;

    auto save_errno = errno;

    if (!ReadFileToString(kSkipMountConfig, &skip_config)) {

    if (!ReadFileToString(kSkipMountConfig, &skip_mount_config)) {

        errno = save_errno;  // missing file is expected

        errno = save_errno;  // missing file is expected

        return true;

        return true;

    }

    }

    return SkipMountWithConfig(skip_mount_config, fstab, verbose);

}





bool SkipMountWithConfig(const std::string& skip_mount_config, Fstab* fstab, bool verbose) {

    std::vector<std::string> skip_mount_patterns;

    std::vector<std::string> skip_mount_patterns;

    for (const auto& line : Split(skip_config, "\n")) {

    for (const auto& line : Split(skip_mount_config, "\n")) {

        if (line.empty() || StartsWith(line, "#")) {

        if (line.empty() || StartsWith(line, "#")) {

            continue;

            continue;

        }

        }
@@ -801,7 +809,6 @@ bool SkipMountingPartitions(Fstab* fstab, bool verbose) { 
    fstab->erase(remove_from, fstab->end());

    fstab->erase(remove_from, fstab->end());

    return true;

    return true;

}

}

#endif





// Loads the fstab file and combines with fstab entries passed in from device tree.

// Loads the fstab file and combines with fstab entries passed in from device tree.

bool ReadDefaultFstab(Fstab* fstab) {

bool ReadDefaultFstab(Fstab* fstab) {

fs_mgr/fuzz/fs_mgr_fstab_fuzzer.cpp

+16 −2
Original line number Original line Diff line number Diff line
@@ -14,13 +14,27 @@ 
// limitations under the License.

// limitations under the License.

//

//





#include <cstdio>

#include <string>

#include <vector>





#include <fstab/fstab.h>

#include <fstab/fstab.h>

#include <fuzzer/FuzzedDataProvider.h>





extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {

extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {

    std::string make_fstab_str(reinterpret_cast<const char*>(data), size);

    FuzzedDataProvider fdp(data, size);



    std::string make_fstab_str = fdp.ConsumeRandomLengthString();

    std::string dsu_slot = fdp.ConsumeRandomLengthString(30);

    std::vector<std::string> dsu_partitions = {

            fdp.ConsumeRandomLengthString(30),

            fdp.ConsumeRandomLengthString(30),

    };

    std::string skip_mount_config = fdp.ConsumeRemainingBytesAsString();



    android::fs_mgr::Fstab fstab;

    android::fs_mgr::Fstab fstab;

    android::fs_mgr::ParseFstabFromString(make_fstab_str, /* proc_mounts = */ false, &fstab);

    android::fs_mgr::ParseFstabFromString(make_fstab_str, /* proc_mounts = */ false, &fstab);

    android::fs_mgr::TransformFstabForDsu(&fstab, dsu_slot, dsu_partitions);

    android::fs_mgr::SkipMountWithConfig(skip_mount_config, &fstab, /* verbose = */ false);



    return 0;

    return 0;

}
 
}

fs_mgr/include_fstab/fstab/fstab.h

+2 −0
Original line number Original line Diff line number Diff line
@@ -97,6 +97,8 @@ using Fstab = std::vector<FstabEntry>; 
bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab* fstab_out);

bool ParseFstabFromString(const std::string& fstab_str, bool proc_mounts, Fstab* fstab_out);

// Exported for testability. Regular users should use ReadDefaultFstab().

// Exported for testability. Regular users should use ReadDefaultFstab().

std::string GetFstabPath();

std::string GetFstabPath();

// Exported for testability.

bool SkipMountWithConfig(const std::string& skip_config, Fstab* fstab, bool verbose);





bool ReadFstabFromFile(const std::string& path, Fstab* fstab);

bool ReadFstabFromFile(const std::string& path, Fstab* fstab);

bool ReadFstabFromDt(Fstab* fstab, bool verbose = true);

bool ReadFstabFromDt(Fstab* fstab, bool verbose = true);