platform_system_core/libcutils/fs_config.c

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* This file is used to define the properties of the filesystem
** images generated by build tools (mkbootfs and mkyaffs2image) and
** by the device side of adb.
*/

#define LOG_TAG "fs_config"

#define _GNU_SOURCE

#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <log/log.h>
#include <private/android_filesystem_config.h>
#include <utils/Compat.h>

#ifndef O_BINARY
#define O_BINARY 0
#endif

/* The following structure is stored little endian */
struct fs_path_config_from_file {
    uint16_t len;
    uint16_t mode;
    uint16_t uid;
    uint16_t gid;
    uint64_t capabilities;
    char prefix[];
} __attribute__((__aligned__(sizeof(uint64_t))));

/* My kingdom for <endian.h> */
static inline uint16_t get2LE(const uint8_t* src) { return src[0] | (src[1] << 8); }

static inline uint64_t get8LE(const uint8_t* src) {
    uint32_t low, high;

    low = src[0] | (src[1] << 8) | (src[2] << 16) | (src[3] << 24);
    high = src[4] | (src[5] << 8) | (src[6] << 16) | (src[7] << 24);
    return ((uint64_t)high << 32) | (uint64_t)low;
}

#define ALIGN(x, alignment) (((x) + ((alignment)-1)) & ~((alignment)-1))

/* Rules for directories.
** These rules are applied based on "first match", so they
** should start with the most specific path and work their
** way up to the root.
*/

static const struct fs_path_config android_dirs[] = {
    /* clang-format off */
    { 00770, AID_SYSTEM,       AID_CACHE,        0, "cache" },
    { 00500, AID_ROOT,         AID_ROOT,         0, "config" },
    { 00771, AID_SYSTEM,       AID_SYSTEM,       0, "data/app" },
    { 00771, AID_SYSTEM,       AID_SYSTEM,       0, "data/app-private" },
    { 00771, AID_SYSTEM,       AID_SYSTEM,       0, "data/app-ephemeral" },
    { 00771, AID_ROOT,         AID_ROOT,         0, "data/dalvik-cache" },
    { 00771, AID_SYSTEM,       AID_SYSTEM,       0, "data/data" },
    { 00771, AID_SHELL,        AID_SHELL,        0, "data/local/tmp" },
    { 00771, AID_SHELL,        AID_SHELL,        0, "data/local" },
    { 00770, AID_DHCP,         AID_DHCP,         0, "data/misc/dhcp" },
    { 00771, AID_SHARED_RELRO, AID_SHARED_RELRO, 0, "data/misc/shared_relro" },
    { 01771, AID_SYSTEM,       AID_MISC,         0, "data/misc" },
    { 00775, AID_MEDIA_RW,     AID_MEDIA_RW,     0, "data/media/Music" },
    { 00775, AID_MEDIA_RW,     AID_MEDIA_RW,     0, "data/media" },
    { 00750, AID_ROOT,         AID_SHELL,        0, "data/nativetest" },
    { 00750, AID_ROOT,         AID_SHELL,        0, "data/nativetest64" },
    { 00775, AID_ROOT,         AID_ROOT,         0, "data/preloads" },
    { 00771, AID_SYSTEM,       AID_SYSTEM,       0, "data" },
    { 00755, AID_ROOT,         AID_SYSTEM,       0, "mnt" },
    { 00755, AID_ROOT,         AID_ROOT,         0, "root" },
    { 00750, AID_ROOT,         AID_SHELL,        0, "sbin" },
    { 00777, AID_ROOT,         AID_ROOT,         0, "sdcard" },
    { 00751, AID_ROOT,         AID_SDCARD_R,     0, "storage" },
    { 00755, AID_ROOT,         AID_SHELL,        0, "system/bin" },
    { 00755, AID_ROOT,         AID_ROOT,         0, "system/etc/ppp" },
    { 00755, AID_ROOT,         AID_SHELL,        0, "system/vendor" },
    { 00755, AID_ROOT,         AID_SHELL,        0, "system/xbin" },
    { 00755, AID_ROOT,         AID_SHELL,        0, "vendor" },
    { 00755, AID_ROOT,         AID_ROOT,         0, 0 },
    /* clang-format on */
};

/* Rules for files.
** These rules are applied based on "first match", so they
** should start with the most specific path and work their
** way up to the root. Prefixes ending in * denotes wildcard
** and will allow partial matches.
*/
static const char sys_conf_dir[] = "/system/etc/fs_config_dirs";
static const char sys_conf_file[] = "/system/etc/fs_config_files";
/* No restrictions are placed on the vendor file-system config files,
 * although the developer is advised to restrict the scope to the /vendor
 * file-system since the intent is to provide support for customized
 * portions of a separate vendor.img.  Has to remain open so that
 * customization can also land on /system/vendor.  We expect build-time
 * checking or filtering when constructing /vendor/etc/fs_config_* files.
 */
static const char ven_conf_dir[] = "/vendor/etc/fs_config_dirs";
static const char ven_conf_file[] = "/vendor/etc/fs_config_files";
static const char* conf[][2] = {
    {sys_conf_file, sys_conf_dir}, {ven_conf_file, ven_conf_dir},
};

static const struct fs_path_config android_files[] = {
    /* clang-format off */
    { 00644, AID_SYSTEM,    AID_SYSTEM,    0, "data/app/*" },
    { 00644, AID_SYSTEM,    AID_SYSTEM,    0, "data/app-ephemeral/*" },
    { 00644, AID_SYSTEM,    AID_SYSTEM,    0, "data/app-private/*" },
    { 00644, AID_APP,       AID_APP,       0, "data/data/*" },
    { 00644, AID_MEDIA_RW,  AID_MEDIA_RW,  0, "data/media/*" },
    { 00640, AID_ROOT,      AID_SHELL,     0, "data/nativetest/tests.txt" },
    { 00640, AID_ROOT,      AID_SHELL,     0, "data/nativetest64/tests.txt" },
    { 00750, AID_ROOT,      AID_SHELL,     0, "data/nativetest/*" },
    { 00750, AID_ROOT,      AID_SHELL,     0, "data/nativetest64/*" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "default.prop" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "odm/build.prop" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "odm/default.prop" },
    { 00750, AID_ROOT,      AID_SHELL,     0, "sbin/fs_mgr" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/bin/crash_dump32" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/bin/crash_dump64" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/bin/debuggerd" },
    { 00750, AID_ROOT,      AID_ROOT,      0, "system/bin/install-recovery.sh" },
    { 00700, AID_ROOT,      AID_ROOT,      0, "system/bin/secilc" },
    { 00750, AID_ROOT,      AID_ROOT,      0, "system/bin/uncrypt" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "system/build.prop" },
    { 00444, AID_ROOT,      AID_ROOT,      0, sys_conf_dir + 1 },
    { 00444, AID_ROOT,      AID_ROOT,      0, sys_conf_file + 1 },
    { 00440, AID_ROOT,      AID_SHELL,     0, "system/etc/init.goldfish.rc" },
    { 00550, AID_ROOT,      AID_SHELL,     0, "system/etc/init.goldfish.sh" },
    { 00550, AID_ROOT,      AID_SHELL,     0, "system/etc/init.ril" },
    { 00555, AID_ROOT,      AID_ROOT,      0, "system/etc/ppp/*" },
    { 00555, AID_ROOT,      AID_ROOT,      0, "system/etc/rc.*" },
    { 00440, AID_ROOT,      AID_ROOT,      0, "system/etc/recovery.img" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "vendor/build.prop" },
    { 00600, AID_ROOT,      AID_ROOT,      0, "vendor/default.prop" },
    { 00444, AID_ROOT,      AID_ROOT,      0, ven_conf_dir + 1 },
    { 00444, AID_ROOT,      AID_ROOT,      0, ven_conf_file + 1 },

    /* the following two files are INTENTIONALLY set-uid, but they
     * are NOT included on user builds. */
    { 06755, AID_ROOT,      AID_ROOT,      0, "system/xbin/procmem" },
    { 04750, AID_ROOT,      AID_SHELL,     0, "system/xbin/su" },

    /* the following files have enhanced capabilities and ARE included
     * in user builds. */
    { 00700, AID_SYSTEM,    AID_SHELL,     CAP_MASK_LONG(CAP_BLOCK_SUSPEND),
                                              "system/bin/inputflinger" },
    { 00550, AID_LOGD,      AID_LOGD,      CAP_MASK_LONG(CAP_SYSLOG) |
                                           CAP_MASK_LONG(CAP_AUDIT_CONTROL) |
                                           CAP_MASK_LONG(CAP_SETGID),
                                              "system/bin/logd" },
    { 00750, AID_ROOT,      AID_SHELL,     CAP_MASK_LONG(CAP_SETUID) |
                                           CAP_MASK_LONG(CAP_SETGID),
                                              "system/bin/run-as" },

    /* Support FIFO scheduling mode in SurfaceFlinger. */
    { 00755, AID_SYSTEM,    AID_GRAPHICS,  CAP_MASK_LONG(CAP_SYS_NICE),
                                              "system/bin/surfaceflinger" },

    /* Support hostapd administering a network interface. */
    { 00755, AID_WIFI,      AID_WIFI,      CAP_MASK_LONG(CAP_NET_ADMIN) |
                                           CAP_MASK_LONG(CAP_NET_RAW),
                                              "system/bin/hostapd" },

    /* Support Bluetooth legacy hal accessing /sys/class/rfkill */
    { 00700, AID_BLUETOOTH, AID_BLUETOOTH, CAP_MASK_LONG(CAP_NET_ADMIN),
                                              "vendor/bin/hw/android.hardware.bluetooth@1.0-service" },

    /* Support wifi_hal_legacy administering a network interface. */
    { 00755, AID_WIFI,      AID_WIFI,      CAP_MASK_LONG(CAP_NET_ADMIN) |
                                           CAP_MASK_LONG(CAP_NET_RAW),
                                              "vendor/bin/hw/android.hardware.wifi@1.0-service" },

    /* A non-privileged zygote that spawns
     * isolated processes for web rendering. */
    { 0750,  AID_ROOT,      AID_ROOT,      CAP_MASK_LONG(CAP_SETUID) |
                                           CAP_MASK_LONG(CAP_SETGID) |
                                           CAP_MASK_LONG(CAP_SETPCAP),
                                              "system/bin/webview_zygote32" },
    { 0750,  AID_ROOT,      AID_ROOT,      CAP_MASK_LONG(CAP_SETUID) |
                                           CAP_MASK_LONG(CAP_SETGID) |
                                           CAP_MASK_LONG(CAP_SETPCAP),
                                              "system/bin/webview_zygote64" },

    /* generic defaults */
    { 00755, AID_ROOT,      AID_ROOT,      0, "bin/*" },
    { 00640, AID_ROOT,      AID_SHELL,     0, "fstab.*" },
    { 00750, AID_ROOT,      AID_SHELL,     0, "init*" },
    { 00750, AID_ROOT,      AID_SHELL,     0, "sbin/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/bin/*" },
    { 00755, AID_ROOT,      AID_ROOT,      0, "system/lib/valgrind/*" },
    { 00755, AID_ROOT,      AID_ROOT,      0, "system/lib64/valgrind/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/vendor/bin/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/vendor/xbin/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "system/xbin/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "vendor/bin/*" },
    { 00755, AID_ROOT,      AID_SHELL,     0, "vendor/xbin/*" },
    { 00644, AID_ROOT,      AID_ROOT,      0, 0 },
    /* clang-format on */
};

static int fs_config_open(int dir, int which, const char* target_out_path) {
    int fd = -1;

    if (target_out_path && *target_out_path) {
        /* target_out_path is the path to the directory holding content of
         * system partition but as we cannot guaranty it ends with '/system'
         * we need this below skip_len logic */
        char* name = NULL;
        int target_out_path_len = strlen(target_out_path);
        int skip_len = strlen("/system");

        if (target_out_path[target_out_path_len] == '/') {
            skip_len++;
        }
        if (asprintf(&name, "%s%s", target_out_path, conf[which][dir] + skip_len) != -1) {
            fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_BINARY));
            free(name);
        }
    }
    if (fd < 0) {
        fd = TEMP_FAILURE_RETRY(open(conf[which][dir], O_RDONLY | O_BINARY));
    }
    return fd;
}

static bool fs_config_cmp(bool dir, const char* prefix, size_t len, const char* path, size_t plen) {
    if (dir) {
        if (plen < len) {
            return false;
        }
    } else {
        /* If name ends in * then allow partial matches. */
        if (prefix[len - 1] == '*') {
            return !strncmp(prefix, path, len - 1);
        }
        if (plen != len) {
            return false;
        }
    }
    return !strncmp(prefix, path, len);
}

void fs_config(const char* path, int dir, const char* target_out_path, unsigned* uid, unsigned* gid,
               unsigned* mode, uint64_t* capabilities) {
    const struct fs_path_config* pc;
    size_t which, plen;

    if (path[0] == '/') {
        path++;
    }

    plen = strlen(path);

    for (which = 0; which < (sizeof(conf) / sizeof(conf[0])); ++which) {
        struct fs_path_config_from_file header;

        int fd = fs_config_open(dir, which, target_out_path);
        if (fd < 0) continue;

        while (TEMP_FAILURE_RETRY(read(fd, &header, sizeof(header))) == sizeof(header)) {
            char* prefix;
            uint16_t host_len = get2LE((const uint8_t*)&header.len);
            ssize_t len, remainder = host_len - sizeof(header);
            if (remainder <= 0) {
                ALOGE("%s len is corrupted", conf[which][dir]);
                break;
            }
            prefix = calloc(1, remainder);
            if (!prefix) {
                ALOGE("%s out of memory", conf[which][dir]);
                break;
            }
            if (TEMP_FAILURE_RETRY(read(fd, prefix, remainder)) != remainder) {
                free(prefix);
                ALOGE("%s prefix is truncated", conf[which][dir]);
                break;
            }
            len = strnlen(prefix, remainder);
            if (len >= remainder) { /* missing a terminating null */
                free(prefix);
                ALOGE("%s is corrupted", conf[which][dir]);
                break;
            }
            if (fs_config_cmp(dir, prefix, len, path, plen)) {
                free(prefix);
                close(fd);
                *uid = get2LE((const uint8_t*)&(header.uid));
                *gid = get2LE((const uint8_t*)&(header.gid));
                *mode = (*mode & (~07777)) | get2LE((const uint8_t*)&(header.mode));
                *capabilities = get8LE((const uint8_t*)&(header.capabilities));
                return;
            }
            free(prefix);
        }
        close(fd);
    }

    for (pc = dir ? android_dirs : android_files; pc->prefix; pc++) {
        if (fs_config_cmp(dir, pc->prefix, strlen(pc->prefix), path, plen)) {
            break;
        }
    }
    *uid = pc->uid;
    *gid = pc->gid;
    *mode = (*mode & (~07777)) | pc->mode;
    *capabilities = pc->capabilities;
}

ssize_t fs_config_generate(char* buffer, size_t length, const struct fs_path_config* pc) {
    struct fs_path_config_from_file* p = (struct fs_path_config_from_file*)buffer;
    size_t len = ALIGN(sizeof(*p) + strlen(pc->prefix) + 1, sizeof(uint64_t));

    if ((length < len) || (len > UINT16_MAX)) {
        return -ENOSPC;
    }
    memset(p, 0, len);
    uint16_t host_len = len;
    p->len = get2LE((const uint8_t*)&host_len);
    p->mode = get2LE((const uint8_t*)&(pc->mode));
    p->uid = get2LE((const uint8_t*)&(pc->uid));
    p->gid = get2LE((const uint8_t*)&(pc->gid));
    p->capabilities = get8LE((const uint8_t*)&(pc->capabilities));
    strcpy(p->prefix, pc->prefix);
    return len;
}