Magisk/native/jni/core/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/sendfile.h>
#include <sys/sysmacros.h>
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#include <functional>
#include <string_view>
#include <xz.h>
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#include <magisk.h>
#include <magiskpolicy.h>
#include <selinux.h>
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#include <cpio.h>
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#include <utils.h>
#include <flags.h>
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#include "binaries.h"
#ifdef USE_64BIT
#include "binaries_arch64.h"
#else
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#include "binaries_arch.h"
#endif
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#include "magiskrc.h"
#define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"
static int test_main(int argc, char *argv[]);
constexpr const char *init_applet[] =
{ "magiskpolicy", "supolicy", "init_test", nullptr };
constexpr int (*init_applet_main[])(int, char *[]) =
{ magiskpolicy_main, magiskpolicy_main, test_main, nullptr };
struct cmdline {
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bool system_as_root;
char slot[3];
char dt_dir[128];
};
struct device {
dev_t major;
dev_t minor;
char devname[32];
char partname[32];
char path[64];
};
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struct raw_data {
void *buf;
size_t sz;
};
static bool unxz(int fd, const uint8_t *buf, size_t size) {
uint8_t out[8192];
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;
}
static void decompress_ramdisk() {
constexpr char tmp[] = "tmp.cpio";
constexpr char ramdisk_xz[] = "ramdisk.cpio.xz";
if (access(ramdisk_xz, F_OK))
return;
uint8_t *buf;
size_t sz;
mmap_ro(ramdisk_xz, buf, sz);
int fd = open(tmp, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC);
unxz(fd, buf, sz);
munmap(buf, sz);
close(fd);
cpio_mmap cpio(tmp);
cpio.extract();
unlink(tmp);
unlink(ramdisk_xz);
}
static int dump_magisk(const char *path, mode_t mode) {
int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, mode);
if (fd < 0)
return 1;
if (!unxz(fd, magisk_xz, sizeof(magisk_xz)))
return 1;
close(fd);
return 0;
}
static int dump_manager(const char *path, mode_t mode) {
int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, mode);
if (fd < 0)
return 1;
if (!unxz(fd, manager_xz, sizeof(manager_xz)))
return 1;
close(fd);
return 0;
}
class MagiskInit {
private:
cmdline cmd{};
raw_data init{};
raw_data config{};
int root = -1;
char **argv;
bool load_sepol = false;
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bool mnt_system = false;
bool mnt_vendor = false;
bool mnt_product = false;
bool mnt_odm = false;
void load_kernel_info();
void preset();
void early_mount();
void setup_rootfs();
bool read_dt_fstab(const char *mnt_point, char *partname, char *partfs);
bool patch_sepolicy();
void cleanup();
public:
explicit MagiskInit(char *argv[]) : argv(argv) {}
void setup_overlay();
void re_exec_init();
void start();
void test();
};
static inline void parse_cmdline(const std::function<void (std::string_view, const char *)> &fn) {
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char cmdline[4096];
int fd = open("/proc/cmdline", O_RDONLY | O_CLOEXEC);
cmdline[read(fd, cmdline, sizeof(cmdline))] = '\0';
close(fd);
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char *tok, *eql, *tmp, *saveptr;
saveptr = cmdline;
while ((tok = strtok_r(nullptr, " \n", &saveptr)) != nullptr) {
eql = strchr(tok, '=');
if (eql) {
*eql = '\0';
if (eql[1] == '"') {
tmp = strchr(saveptr, '"');
if (tmp != nullptr) {
*tmp = '\0';
saveptr[-1] = ' ';
saveptr = tmp + 1;
eql++;
}
}
fn(tok, eql + 1);
} else {
fn(tok, "");
}
}
}
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void MagiskInit::load_kernel_info() {
// 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);
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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);
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bool skip_initramfs = false;
bool enter_recovery = false;
bool kirin = false;
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parse_cmdline([&](auto key, auto value) -> void {
LOGD("cmdline: [%s]=[%s]\n", key.data(), value);
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if (key == "androidboot.slot_suffix") {
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strcpy(cmd.slot, value);
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} else if (key == "androidboot.slot") {
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cmd.slot[0] = '_';
strcpy(cmd.slot + 1, value);
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} else if (key == "skip_initramfs") {
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skip_initramfs = true;
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} else if (key == "androidboot.android_dt_dir") {
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strcpy(cmd.dt_dir, value);
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} else if (key == "enter_recovery") {
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enter_recovery = value[0] == '1';
} else if (key == "androidboot.hardware") {
kirin = strstr(value, "kirin") || strstr(value, "hi3660");
}
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});
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if (kirin && enter_recovery) {
// Inform that we are actually booting as recovery
if (FILE *f = fopen("/.backup/.magisk", "ae"); f) {
fprintf(f, "RECOVERYMODE=true\n");
fclose(f);
}
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cmd.system_as_root = true;
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}
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cmd.system_as_root |= skip_initramfs;
if (cmd.dt_dir[0] == '\0')
strcpy(cmd.dt_dir, DEFAULT_DT_DIR);
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LOGD("system_as_root[%d] slot[%s] dt_dir[%s]\n", cmd.system_as_root, cmd.slot, cmd.dt_dir);
}
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void MagiskInit::preset() {
root = open("/", O_RDONLY | O_CLOEXEC);
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if (cmd.system_as_root) {
// Clear rootfs
const char *excl[] = { "overlay", "proc", "sys", nullptr };
excl_list = excl;
frm_rf(root);
excl_list = nullptr;
} else {
decompress_ramdisk();
// Revert original init binary
rename("/.backup/init", "/init");
rm_rf("/.backup");
// Do not go further if device is booting into recovery
if (access("/sbin/recovery", F_OK) == 0)
re_exec_init();
}
}
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static inline 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)
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return false;
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 inline bool is_lnk(const char *name) {
struct stat st;
if (lstat(name, &st))
return false;
return S_ISLNK(st.st_mode);
}
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#define link_root(part) \
if (is_lnk("/system_root" part)) \
cp_afc("/system_root" part, part)
#define mount_root(part) \
if (!is_lnk("/" #part) && read_dt_fstab(#part, partname, fstype)) { \
setup_block(&dev, partname); \
xmkdir("/" #part, 0755); \
xmount(dev.path, "/" #part, fstype, MS_RDONLY, nullptr); \
mnt_##part = true; \
}
void MagiskInit::early_mount() {
struct device dev;
char partname[32];
char fstype[32];
if (cmd.system_as_root) {
sprintf(partname, "system%s", cmd.slot);
setup_block(&dev, partname);
xmkdir("/system_root", 0755);
xmount(dev.path, "/system_root", "ext4", MS_RDONLY, nullptr);
xmkdir("/system", 0755);
xmount("/system_root/system", "/system", nullptr, MS_BIND, nullptr);
// Android Q
if (is_lnk("/system_root/init"))
load_sepol = true;
// System-as-root with monolithic sepolicy
if (access("/system_root/sepolicy", F_OK) == 0)
cp_afc("/system_root/sepolicy", "/sepolicy");
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// Copy if these partitions are symlinks
link_root("/vendor");
link_root("/product");
link_root("/odm");
} else {
mount_root(system);
}
mount_root(vendor);
mount_root(product);
mount_root(odm);
}
void MagiskInit::setup_rootfs() {
bool patch_init = patch_sepolicy();
if (cmd.system_as_root) {
// Clone rootfs except /system
int system_root = open("/system_root", O_RDONLY | O_CLOEXEC);
const char *excl[] = { "system", nullptr };
excl_list = excl;
clone_dir(system_root, root);
close(system_root);
excl_list = nullptr;
}
// Override /sepolicy if exist
rename("/magisk_sepolicy", "/sepolicy");
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if (patch_init) {
constexpr char SYSTEM_INIT[] = "/system/bin/init";
// If init is symlink, copy it to rootfs so we can patch
struct stat st;
lstat("/init", &st);
if (S_ISLNK(st.st_mode))
cp_afc(SYSTEM_INIT, "/init");
char *addr;
size_t size;
mmap_rw("/init", addr, size);
for (char *p = addr; p < addr + size; ++p) {
if (memcmp(p, SPLIT_PLAT_CIL, sizeof(SPLIT_PLAT_CIL)) == 0) {
// Force init to load /sepolicy
memset(p, 'x', sizeof(SPLIT_PLAT_CIL) - 1);
p += sizeof(SPLIT_PLAT_CIL) - 1;
} else if (memcmp(p, SYSTEM_INIT, sizeof(SYSTEM_INIT)) == 0) {
// Force execute /init instead of /system/bin/init
strcpy(p, "/init");
p += sizeof(SYSTEM_INIT) - 1;
}
}
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munmap(addr, size);
}
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// 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
FILE *rc = xfopen("/init.rc", "ae");
char pfd_svc[8], ls_svc[8];
gen_rand_str(pfd_svc, sizeof(pfd_svc));
do {
gen_rand_str(ls_svc, sizeof(ls_svc));
} while (strcmp(pfd_svc, ls_svc) == 0);
fprintf(rc, magiskrc, pfd_svc, pfd_svc, ls_svc);
fclose(rc);
// Don't let init run in init yet
lsetfilecon("/init", "u:object_r:rootfs:s0");
// Create hardlink mirror of /sbin to /root
mkdir("/root", 0750);
clone_attr("/sbin", "/root");
int rootdir = xopen("/root", O_RDONLY | O_CLOEXEC);
int sbin = xopen("/sbin", O_RDONLY | O_CLOEXEC);
link_dir(sbin, rootdir);
}
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bool MagiskInit::patch_sepolicy() {
bool patch_init = false;
if (access(SPLIT_PLAT_CIL, R_OK) == 0)
patch_init = true; /* Split sepolicy */
else if (access("/sepolicy", R_OK) == 0)
load_policydb("/sepolicy"); /* Monolithic sepolicy */
else
return false; /* No SELinux */
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// Mount selinuxfs to communicate with kernel
xmount("selinuxfs", SELINUX_MNT, "selinuxfs", 0, nullptr);
if (patch_init)
load_split_cil();
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sepol_magisk_rules();
sepol_allow(SEPOL_PROC_DOMAIN, ALL, ALL, ALL);
dump_policydb("/magisk_sepolicy");
// Load policy to kernel so we can label rootfs
if (load_sepol)
dump_policydb(SELINUX_LOAD);
// Remove OnePlus stupid debug sepolicy and use our own
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if (access("/sepolicy_debug", F_OK) == 0) {
unlink("/sepolicy_debug");
link("/magisk_sepolicy", "/sepolicy_debug");
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}
// Enable selinux functions
selinux_builtin_impl();
return patch_init;
}
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bool MagiskInit::read_dt_fstab(const char *mnt_point, char *partname, char *partfs) {
char path[128];
int fd;
sprintf(path, "%s/fstab/%s/dev", cmd.dt_dir, mnt_point);
if ((fd = xopen(path, O_RDONLY | O_CLOEXEC)) >= 0) {
read(fd, path, sizeof(path));
close(fd);
char *name = rtrim(strrchr(path, '/') + 1);
sprintf(partname, "%s%s", name, strend(name, cmd.slot) ? cmd.slot : "");
sprintf(path, "%s/fstab/%s/type", cmd.dt_dir, mnt_point);
if ((fd = xopen(path, O_RDONLY | O_CLOEXEC)) >= 0) {
read(fd, partfs, 32);
close(fd);
return true;
}
}
return false;
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}
#define umount_root(part) \
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if (mnt_##part) \
umount("/" #part);
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void MagiskInit::cleanup() {
umount(SELINUX_MNT);
umount("/sys");
umount("/proc");
umount_root(system);
umount_root(vendor);
umount_root(product);
umount_root(odm);
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}
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static inline 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, 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);
}
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void MagiskInit::setup_overlay() {
char path[128];
int fd;
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// Wait for early-init start
while (access(EARLYINIT, F_OK) != 0)
usleep(10);
setcon("u:r:" SEPOL_PROC_DOMAIN ":s0");
unlink(EARLYINIT);
// Mount the /sbin tmpfs overlay
xmount("tmpfs", "/sbin", "tmpfs", 0, nullptr);
chmod("/sbin", 0755);
setfilecon("/sbin", "u:object_r:rootfs:s0");
// Dump binaries
mkdir(MAGISKTMP, 0755);
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fd = xopen(MAGISKTMP "/config", O_WRONLY | O_CREAT, 0000);
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write(fd, config.buf, config.sz);
close(fd);
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fd = xopen("/sbin/magiskinit", O_WRONLY | O_CREAT, 0755);
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write(fd, init.buf, init.sz);
close(fd);
dump_magisk("/sbin/magisk", 0755);
patch_socket_name("/sbin/magisk");
setfilecon("/sbin/magisk", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/sbin/magiskinit", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
// Create applet symlinks
for (int i = 0; applet_names[i]; ++i) {
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sprintf(path, "/sbin/%s", applet_names[i]);
xsymlink("/sbin/magisk", path);
}
for (int i = 0; init_applet[i]; ++i) {
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sprintf(path, "/sbin/%s", init_applet[i]);
xsymlink("/sbin/magiskinit", path);
}
// Create symlinks pointing back to /root
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DIR *dir = xopendir("/root");
struct dirent *entry;
fd = xopen("/sbin", O_RDONLY);
while((entry = xreaddir(dir))) {
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if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
snprintf(path, PATH_MAX, "/root/%s", entry->d_name);
xsymlinkat(path, fd, entry->d_name);
}
closedir(dir);
close(fd);
close(xopen(EARLYINITDONE, O_RDONLY | O_CREAT, 0));
exit(0);
}
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void MagiskInit::re_exec_init() {
cleanup();
execv("/init", argv);
exit(1);
}
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void MagiskInit::start() {
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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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full_read("/init", &init.buf, &init.sz);
full_read("/.backup/.magisk", &config.buf, &config.sz);
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load_kernel_info();
preset();
early_mount();
setup_rootfs();
}
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void MagiskInit::test() {
cmdline_logging();
log_cb.ex = nop_ex;
chdir(dirname(argv[0]));
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chroot(".");
chdir("/");
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load_kernel_info();
preset();
early_mount();
setup_rootfs();
cleanup();
}
static int test_main(int argc, char *argv[]) {
MagiskInit init(argv);
init.test();
return 0;
}
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int main(int argc, char *argv[]) {
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) {
if (strcmp(argv[2], "magisk") == 0)
return dump_magisk(argv[3], 0755);
else if (strcmp(argv[2], "manager") == 0)
return dump_manager(argv[3], 0644);
}
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MagiskInit init(argv);
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// Run the main routine
init.start();
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// Close all file descriptors
for (int i = 0; i < 30; ++i)
close(i);
// Launch daemon to setup overlay
if (fork_dont_care() == 0)
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init.setup_overlay();
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init.re_exec_init();
}