Magisk/native/jni/misc/init.cpp

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/* init.cpp - Pre-init Magisk support
*
* This code has to be compiled statically to work properly.
*
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* To unify Magisk support for both legacy "normal" devices and new skip_initramfs devices,
* magisk binary compilation is split into two parts - first part only compiles "magisk".
* The python build script will load the magisk main binary and compress with lzma2, dumping
* the results into "dump.h". The "magisk" binary is embedded into this binary, and will
* get extracted to the overlay folder along with init.magisk.rc.
*
* This tool does all pre-init operations to setup a Magisk environment, which pathces rootfs
* on the fly, providing fundamental support such as init, init.rc, and sepolicy patching.
*
* Magiskinit is also responsible for constructing a proper rootfs on skip_initramfs devices.
* On skip_initramfs devices, it will parse kernel cmdline, mount sysfs, parse through
* uevent files to make the system (or vendor if available) block device node, then copy
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* rootfs files from system.
*
* This tool will be replaced with the real init to continue the boot process, but hardlinks are
* preserved as it also provides CLI for sepolicy patching (magiskpolicy)
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <fcntl.h>
#include <libgen.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/mman.h>
#include <sys/sendfile.h>
#include <sys/sysmacros.h>
#include <xz.h>
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#include "binaries.h"
#include "binaries_arch.h"
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#include "magiskrc.h"
#include "magisk.h"
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#include "magiskpolicy.h"
#include "utils.h"
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#include "flags.h"
#define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"
int (*init_applet_main[]) (int, char *[]) = { magiskpolicy_main, magiskpolicy_main, nullptr };
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static int root = -1;
static bool mnt_system = false;
static bool mnt_vendor = false;
struct cmdline {
bool skip_initramfs;
char slot[3];
char dt_dir[128];
};
struct device {
dev_t major;
dev_t minor;
char devname[32];
char partname[32];
char path[64];
};
static void parse_cmdline(struct cmdline *cmd) {
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// cleanup
memset(cmd, 0, sizeof(*cmd));
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char cmdline[4096];
int fd = open("/proc/cmdline", O_RDONLY | O_CLOEXEC);
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cmdline[read(fd, cmdline, sizeof(cmdline))] = '\0';
close(fd);
for (char *tok = strtok(cmdline, " "); tok; tok = strtok(nullptr, " ")) {
if (strncmp(tok, "androidboot.slot_suffix", 23) == 0) {
sscanf(tok, "androidboot.slot_suffix=%s", cmd->slot);
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} else if (strncmp(tok, "androidboot.slot", 16) == 0) {
cmd->slot[0] = '_';
sscanf(tok, "androidboot.slot=%c", cmd->slot + 1);
} else if (strcmp(tok, "skip_initramfs") == 0) {
cmd->skip_initramfs = true;
} else if (strncmp(tok, "androidboot.android_dt_dir", 26) == 0) {
sscanf(tok, "androidboot.android_dt_dir=%s", cmd->dt_dir);
}
}
if (cmd->dt_dir[0] == '\0')
strcpy(cmd->dt_dir, DEFAULT_DT_DIR);
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LOGD("cmdline: skip_initramfs[%d] slot[%s] dt_dir[%s]\n", cmd->skip_initramfs, cmd->slot, cmd->dt_dir);
}
static void parse_device(struct device *dev, const char *uevent) {
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dev->partname[0] = '\0';
FILE *fp = xfopen(uevent, "r");
char buf[64];
while (fgets(buf, sizeof(buf), fp)) {
if (strncmp(buf, "MAJOR", 5) == 0) {
sscanf(buf, "MAJOR=%ld", (long*) &dev->major);
} else if (strncmp(buf, "MINOR", 5) == 0) {
sscanf(buf, "MINOR=%ld", (long*) &dev->minor);
} else if (strncmp(buf, "DEVNAME", 7) == 0) {
sscanf(buf, "DEVNAME=%s", dev->devname);
} else if (strncmp(buf, "PARTNAME", 8) == 0) {
sscanf(buf, "PARTNAME=%s", dev->partname);
}
}
fclose(fp);
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LOGD("%s [%s] (%u, %u)\n", dev->devname, dev->partname, (unsigned) dev->major, (unsigned) dev->minor);
}
static bool setup_block(struct device *dev, const char *partname) {
char path[128];
struct dirent *entry;
DIR *dir = opendir("/sys/dev/block");
if (dir == nullptr)
return 1;
bool found = false;
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
sprintf(path, "/sys/dev/block/%s/uevent", entry->d_name);
parse_device(dev, path);
if (strcasecmp(dev->partname, partname) == 0) {
sprintf(dev->path, "/dev/block/%s", dev->devname);
found = true;
break;
}
}
closedir(dir);
if (!found)
return false;
mkdir("/dev", 0755);
mkdir("/dev/block", 0755);
mknod(dev->path, S_IFBLK | 0600, makedev(dev->major, dev->minor));
return true;
}
static bool read_fstab_dt(const struct cmdline *cmd, const char *mnt_point, char *partname) {
char buf[128];
struct stat st;
sprintf(buf, "/%s", mnt_point);
lstat(buf, &st);
// Don't early mount if the mount point is symlink
if (S_ISLNK(st.st_mode))
return false;
sprintf(buf, "%s/fstab/%s/dev", cmd->dt_dir, mnt_point);
if (access(buf, F_OK) == 0) {
int fd = open(buf, O_RDONLY | O_CLOEXEC);
read(fd, buf, sizeof(buf));
close(fd);
char *name = strrchr(buf, '/') + 1;
sprintf(partname, "%s%s", name, strend(name, cmd->slot) ? cmd->slot : "");
return true;
}
return false;
}
static bool verify_precompiled() {
DIR *dir;
struct dirent *entry;
int fd;
char sys_sha[64], ven_sha[64];
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// init the strings with different value
sys_sha[0] = 0;
ven_sha[0] = 1;
dir = opendir(NONPLAT_POLICY_DIR);
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".sha256") == 0) {
fd = openat(dirfd(dir), entry->d_name, O_RDONLY | O_CLOEXEC);
read(fd, ven_sha, sizeof(ven_sha));
close(fd);
break;
}
}
closedir(dir);
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dir = opendir(PLAT_POLICY_DIR);
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".sha256") == 0) {
fd = openat(dirfd(dir), entry->d_name, O_RDONLY | O_CLOEXEC);
read(fd, sys_sha, sizeof(sys_sha));
close(fd);
break;
}
}
closedir(dir);
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LOGD("sys_sha[%.*s]\nven_sha[%.*s]\n", sizeof(sys_sha), sys_sha, sizeof(ven_sha), ven_sha);
return memcmp(sys_sha, ven_sha, sizeof(sys_sha)) == 0;
}
static bool patch_sepolicy() {
bool init_patch = false;
if (access(SPLIT_PRECOMPILE, R_OK) == 0 && verify_precompiled()) {
init_patch = true;
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load_policydb(SPLIT_PRECOMPILE);
} else if (access(SPLIT_PLAT_CIL, R_OK) == 0) {
init_patch = true;
compile_split_cil();
} else if (access("/sepolicy", R_OK) == 0) {
load_policydb("/sepolicy");
} else {
return false;
}
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sepol_magisk_rules();
sepol_allow(SEPOL_PROC_DOMAIN, ALL, ALL, ALL);
dump_policydb("/sepolicy");
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// Remove the stupid debug sepolicy and use our own
if (access("/sepolicy_debug", F_OK) == 0) {
unlink("/sepolicy_debug");
link("/sepolicy", "/sepolicy_debug");
}
if (init_patch) {
// Force init to load /sepolicy
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uint8_t *addr;
size_t size;
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mmap_rw("/init", (void **) &addr, &size);
for (int i = 0; i < size; ++i) {
if (memcmp(addr + i, SPLIT_PLAT_CIL, sizeof(SPLIT_PLAT_CIL) - 1) == 0) {
memcpy(addr + i + sizeof(SPLIT_PLAT_CIL) - 4, "xxx", 3);
break;
}
}
munmap(addr, size);
}
return true;
}
static bool unxz(int fd, const uint8_t *buf, size_t size) {
uint8_t out[8192];
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xz_crc32_init();
struct xz_dec *dec = xz_dec_init(XZ_DYNALLOC, 1 << 26);
struct xz_buf b = {
.in = buf,
.in_pos = 0,
.in_size = size,
.out = out,
.out_pos = 0,
.out_size = sizeof(out)
};
enum xz_ret ret;
do {
ret = xz_dec_run(dec, &b);
if (ret != XZ_OK && ret != XZ_STREAM_END)
return false;
write(fd, out, b.out_pos);
b.out_pos = 0;
} while (b.in_pos != size);
return true;
}
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static int dump_magisk(const char *path, mode_t mode) {
int fd = creat(path, mode);
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if (fd < 0)
return 1;
if (!unxz(fd, magisk_xz, sizeof(magisk_xz)))
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return 1;
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close(fd);
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return 0;
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}
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static int dump_manager(const char *path, mode_t mode) {
int fd = creat(path, mode);
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if (fd < 0)
return 1;
if (!unxz(fd, manager_xz, sizeof(manager_xz)))
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return 1;
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close(fd);
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return 0;
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}
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static int dump_magiskrc(const char *path, mode_t mode) {
int fd = creat(path, mode);
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if (fd < 0)
return 1;
char startup_svc[8], late_start_svc[8], rc[sizeof(magiskrc) + 100];
gen_rand_str(startup_svc, sizeof(startup_svc));
do {
gen_rand_str(late_start_svc, sizeof(late_start_svc));
} while (strcmp(startup_svc, late_start_svc) == 0);
int size = sprintf(rc, magiskrc, startup_svc, startup_svc, late_start_svc);
xwrite(fd, rc, size);
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close(fd);
return 0;
}
static void patch_socket_name(const char *path) {
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uint8_t *buf;
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char name[sizeof(MAIN_SOCKET)];
size_t size;
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mmap_rw(path, (void **) &buf, &size);
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for (int i = 0; i < size; ++i) {
if (memcmp(buf + i, MAIN_SOCKET, sizeof(MAIN_SOCKET)) == 0) {
gen_rand_str(name, sizeof(name));
memcpy(buf + i, name, sizeof(name));
i += sizeof(name);
}
if (memcmp(buf + i, LOG_SOCKET, sizeof(LOG_SOCKET)) == 0) {
gen_rand_str(name, sizeof(name));
memcpy(buf + i, name, sizeof(name));
i += sizeof(name);
}
}
munmap(buf, size);
}
static void exec_init(char *argv[]) {
// Clean up
close(root);
umount("/proc");
umount("/sys");
if (mnt_system)
umount("/system");
if (mnt_vendor)
umount("/vendor");
execv("/init", argv);
}
int main(int argc, char *argv[]) {
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umask(0);
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for (int i = 0; init_applet[i]; ++i) {
if (strcmp(basename(argv[0]), init_applet[i]) == 0)
return (*init_applet_main[i])(argc, argv);
}
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if (argc > 1 && strcmp(argv[1], "-x") == 0) {
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if (strcmp(argv[2], "magisk") == 0)
return dump_magisk(argv[3], 0755);
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else if (strcmp(argv[2], "manager") == 0)
return dump_manager(argv[3], 0644);
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else if (strcmp(argv[2], "magiskrc") == 0)
return dump_magiskrc(argv[3], 0755);
}
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// Prevent file descriptor confusion
mknod("/null", S_IFCHR | 0666, makedev(1, 3));
int null = open("/null", O_RDWR | O_CLOEXEC);
unlink("/null");
xdup3(null, STDIN_FILENO, O_CLOEXEC);
xdup3(null, STDOUT_FILENO, O_CLOEXEC);
xdup3(null, STDERR_FILENO, O_CLOEXEC);
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if (null > STDERR_FILENO)
close(null);
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// Backup self
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rename("/init", "/init.bak");
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// Communicate with kernel using procfs and sysfs
mkdir("/proc", 0755);
xmount("proc", "/proc", "proc", 0, nullptr);
mkdir("/sys", 0755);
xmount("sysfs", "/sys", "sysfs", 0, nullptr);
struct cmdline cmd;
parse_cmdline(&cmd);
/* ***********
* Initialize
* ***********/
root = open("/", O_RDONLY | O_CLOEXEC);
if (cmd.skip_initramfs) {
// Clear rootfs
const char *excl[] = { "overlay", ".backup", "proc", "sys", "init.bak", nullptr };
excl_list = excl;
frm_rf(root);
excl_list = nullptr;
} else {
// Revert original init binary
link("/.backup/init", "/init");
}
// Do not go further if system_root device is booting as recovery
if (!cmd.skip_initramfs && access("/sbin/recovery", F_OK) == 0) {
// Remove Magisk traces
rm_rf("/.backup");
exec_init(argv);
}
/* ************
* Early Mount
* ************/
struct device dev;
char partname[32];
if (cmd.skip_initramfs) {
sprintf(partname, "system%s", cmd.slot);
setup_block(&dev, partname);
xmkdir("/system_root", 0755);
xmount(dev.path, "/system_root", "ext4", MS_RDONLY, nullptr);
int system_root = open("/system_root", O_RDONLY | O_CLOEXEC);
// Clone rootfs except /system
const char *excl[] = { "system", nullptr };
excl_list = excl;
clone_dir(system_root, root);
close(system_root);
excl_list = nullptr;
xmkdir("/system", 0755);
xmount("/system_root/system", "/system", nullptr, MS_BIND, nullptr);
} else if (read_fstab_dt(&cmd, "system", partname)) {
setup_block(&dev, partname);
xmount(dev.path, "/system", "ext4", MS_RDONLY, nullptr);
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mnt_system = true;
}
if (read_fstab_dt(&cmd, "vendor", partname)) {
setup_block(&dev, partname);
xmount(dev.path, "/vendor", "ext4", MS_RDONLY, nullptr);
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mnt_vendor = true;
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}
/* ****************
* Ramdisk Patches
* ****************/
// Handle ramdisk overlays
int fd = open("/overlay", O_RDONLY | O_CLOEXEC);
if (fd >= 0) {
mv_dir(fd, root);
close(fd);
rmdir("/overlay");
}
// Patch init.rc to load magisk scripts
bool injected = false;
char line[4096];
FILE *fp = xfopen("/init.rc", "r");
fd = creat("/init.rc.new", 0750);
while(fgets(line, sizeof(line), fp)) {
if (!injected && strncmp(line, "import", 6) == 0) {
if (strstr(line, "init.magisk.rc")) {
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injected = true;
} else {
xwrite(fd, "import /init.magisk.rc\n", 23);
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injected = true;
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}
} else if (strstr(line, "selinux.reload_policy")) {
// Do not allow sepolicy patch
continue;
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}
xwrite(fd, line, strlen(line));
}
fclose(fp);
close(fd);
rename("/init.rc.new", "/init.rc");
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// Patch sepolicy
patch_sepolicy();
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// Dump binaries
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dump_magiskrc(MAGISKRC, 0750);
dump_magisk("/sbin/magisk", 0755);
patch_socket_name("/sbin/magisk");
rename("/init.bak", "/sbin/magiskinit");
exec_init(argv);
}