Magisk/jni/magiskinit.c

413 lines
11 KiB
C

/* magiskinit.c - Workaround for skip_initramfs devices
*
* This code has to be compiled statically to work properly.
*
* Magiskinit will mount sysfs, parse through uevent files to make the system block device,
* then it'll mount the system partition and clone rootfs except files under /system.
* Folders placed in "overlay" will then be overlayed to the root.
* Lastly, before giving control back to the real init, it'll patch the root files,
* extract (or compile if needed) sepolicy and patch it to load Magisk.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <fcntl.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 <cil/cil.h>
#include "magiskpolicy.h"
struct cmdline {
int skip_initramfs;
char slot[3];
};
struct device {
dev_t major;
dev_t minor;
char devname[32];
char partname[32];
char path[64];
};
extern policydb_t *policydb;
extern void mmap_ro(const char *filename, void **buf, size_t *size);
extern void mmap_rw(const char *filename, void **buf, size_t *size);
extern void *patch_init_rc(char *data, uint32_t *size);
static void clone_dir(int src, int dest) {
struct dirent *entry;
DIR *dir;
int srcfd, destfd, newsrc, newdest;
struct stat st;
char buf[PATH_MAX];
ssize_t size;
dir = fdopendir(src);
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
fstatat(src, entry->d_name, &st, AT_SYMLINK_NOFOLLOW);
switch (entry->d_type) {
case DT_DIR:
mkdirat(dest, entry->d_name, st.st_mode & 0777);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, 0);
// Don't clone recursive if it's /system
if (strcmp(entry->d_name, "system") == 0)
continue;
newsrc = openat(src, entry->d_name, O_RDONLY | O_CLOEXEC);
newdest = openat(dest, entry->d_name, O_RDONLY | O_CLOEXEC);
clone_dir(newsrc, newdest);
close(newsrc);
close(newdest);
break;
case DT_REG:
destfd = openat(dest, entry->d_name, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, st.st_mode & 0777);
srcfd = openat(src, entry->d_name, O_RDONLY | O_CLOEXEC);
sendfile(destfd, srcfd, 0, st.st_size);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, 0);
close(destfd);
close(srcfd);
break;
case DT_LNK:
size = readlinkat(src, entry->d_name, buf, sizeof(buf));
buf[size] = '\0';
symlinkat(buf, dest, entry->d_name);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, AT_SYMLINK_NOFOLLOW);
break;
}
}
}
static void mv_dir(int src, int dest) {
struct dirent *entry;
DIR *dir;
int newsrc, newdest;
struct stat st;
char buf[PATH_MAX];
ssize_t size;
dir = fdopendir(src);
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
fstatat(src, entry->d_name, &st, AT_SYMLINK_NOFOLLOW);
switch (entry->d_type) {
case DT_DIR:
mkdirat(dest, entry->d_name, st.st_mode & 0777);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, 0);
newsrc = openat(src, entry->d_name, O_RDONLY | O_CLOEXEC);
newdest = openat(dest, entry->d_name, O_RDONLY | O_CLOEXEC);
mv_dir(newsrc, newdest);
close(newsrc);
close(newdest);
break;
case DT_REG:
renameat(src, entry->d_name, dest, entry->d_name);
fchmodat(dest, entry->d_name, st.st_mode & 0777, 0);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, 0);
break;
case DT_LNK:
size = readlinkat(src, entry->d_name, buf, sizeof(buf));
buf[size] = '\0';
symlinkat(buf, dest, entry->d_name);
fchownat(dest, entry->d_name, st.st_uid, st.st_gid, AT_SYMLINK_NOFOLLOW);
break;
}
unlinkat(src, entry->d_name, AT_REMOVEDIR);
}
}
static void rm_rf(int path) {
struct dirent *entry;
int newfd;
DIR *dir = fdopendir(path);
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
switch (entry->d_type) {
case DT_DIR:
// Preserve overlay
if (strcmp(entry->d_name, "overlay") == 0)
continue;
newfd = openat(path, entry->d_name, O_RDONLY | O_CLOEXEC);
rm_rf(newfd);
close(newfd);
unlinkat(path, entry->d_name, AT_REMOVEDIR);
break;
default:
unlinkat(path, entry->d_name, 0);
break;
}
}
}
static void parse_cmdline(struct cmdline *cmd) {
char *tok;
char buffer[4096];
mkdir("/proc", 0555);
mount("proc", "/proc", "proc", 0, NULL);
int fd = open("/proc/cmdline", O_RDONLY | O_CLOEXEC);
ssize_t size = read(fd, buffer, sizeof(buffer));
buffer[size] = '\0';
close(fd);
umount("/proc");
tok = strtok(buffer, " ");
cmd->skip_initramfs = 0;
cmd->slot[0] = '\0';
while (tok != NULL) {
if (strncmp(tok, "androidboot.slot_suffix", 23) == 0) {
sscanf(tok, "androidboot.slot_suffix=%s", cmd->slot);
} else if (strcmp(tok, "skip_initramfs") == 0) {
cmd->skip_initramfs = 1;
break;
}
tok = strtok(NULL, " ");
}
}
static void parse_device(struct device *dev, char *uevent) {
char *tok;
tok = strtok(uevent, "\n");
while (tok != NULL) {
if (strncmp(tok, "MAJOR", 5) == 0) {
sscanf(tok, "MAJOR=%ld", (long*) &dev->major);
} else if (strncmp(tok, "MINOR", 5) == 0) {
sscanf(tok, "MINOR=%ld", (long*) &dev->minor);
} else if (strncmp(tok, "DEVNAME", 7) == 0) {
sscanf(tok, "DEVNAME=%s", dev->devname);
} else if (strncmp(tok, "PARTNAME", 8) == 0) {
sscanf(tok, "PARTNAME=%s", dev->partname);
}
tok = strtok(NULL, "\n");
}
}
static int setup_block(struct device *dev, const char *partname) {
char buffer[1024], path[128];
struct dirent *entry;
DIR *dir = opendir("/sys/dev/block");
if (dir == NULL)
return 1;
int found = 0;
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
snprintf(path, sizeof(path), "/sys/dev/block/%s/uevent", entry->d_name);
int fd = open(path, O_RDONLY | O_CLOEXEC);
ssize_t size = read(fd, buffer, sizeof(buffer));
buffer[size] = '\0';
close(fd);
parse_device(dev, buffer);
if (strcmp(dev->partname, partname) == 0) {
snprintf(dev->path, sizeof(dev->path), "/dev/block/%s", dev->devname);
found = 1;
break;
}
}
closedir(dir);
if (!found)
return 1;
mkdir("/dev", 0755);
mkdir("/dev/block", 0755);
mknod(dev->path, S_IFBLK | 0600, makedev(dev->major, dev->minor));
return 0;
}
static void patch_ramdisk() {
void *addr;
size_t size;
mmap_rw("/init", &addr, &size);
for (int i = 0; i < size; ++i) {
if (memcmp(addr + i, "/system/etc/selinux/plat_sepolicy.cil", 37) == 0) {
memcpy(addr + i, "/system/etc/selinux/plat_sepolicy.xxx", 37);
break;
}
}
munmap(addr, size);
mmap_rw("/init.rc", &addr, &size);
uint32_t new_size = size;
void *init_rc = patch_init_rc(addr, &new_size);
munmap(addr, size);
int fd = open("/init.rc", O_WRONLY | O_TRUNC | O_CLOEXEC);
write(fd, init_rc, new_size);
close(fd);
free(init_rc);
}
static int strend(const char *s1, const char *s2) {
int l1 = strlen(s1);
int l2 = strlen(s2);
return strcmp(s1 + l1 - l2, s2);
}
static void patch_sepolicy() {
DIR *dir;
struct dirent *entry;
char *sepolicy = NULL, path[128];
if (access("/system_root/sepolicy", R_OK) == 0)
sepolicy = "/system_root/sepolicy";
if (sepolicy == NULL && access("/vendor/etc/selinux/precompiled_sepolicy", R_OK) == 0) {
void *sys_sha = NULL, *ven_sha = NULL;
size_t sys_size = 0, ven_size = 0;
if ((dir = opendir("/vendor/etc/selinux")) == NULL)
goto check_done;
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".sha256") == 0) {
snprintf(path, sizeof(path), "/vendor/etc/selinux/%s", entry->d_name);
mmap_ro(path, &ven_sha, &ven_size);
break;
}
}
closedir(dir);
if ((dir = opendir("/system/etc/selinux")) == NULL)
goto check_done;
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".sha256") == 0) {
snprintf(path, sizeof(path), "/system/etc/selinux/%s", entry->d_name);
mmap_ro(path, &sys_sha, &sys_size);
break;
}
}
closedir(dir);
if (sys_size == ven_size && memcmp(sys_sha, ven_sha, sys_size) == 0)
sepolicy = "/vendor/etc/selinux/precompiled_sepolicy";
munmap(sys_sha, sys_size);
munmap(ven_sha, ven_size);
}
check_done:
if (sepolicy) {
load_policydb(sepolicy);
} else {
// Compile cil
struct cil_db *db = NULL;
sepol_policydb_t *pdb = NULL;
void *addr;
size_t size;
cil_db_init(&db);
cil_set_mls(db, 1);
cil_set_target_platform(db, SEPOL_TARGET_SELINUX);
cil_set_policy_version(db, POLICYDB_VERSION_XPERMS_IOCTL);
cil_set_attrs_expand_generated(db, 0);
mmap_ro("/system/etc/selinux/plat_sepolicy.cil", &addr, &size);
cil_add_file(db, "/system/etc/selinux/plat_sepolicy.cil", addr, size);
munmap(addr, size);
dir = opendir("/system/etc/selinux/mapping");
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".cil") == 0) {
snprintf(path, sizeof(path), "/system/etc/selinux/mapping/%s", entry->d_name);
mmap_ro(path, &addr, &size);
cil_add_file(db, path, addr, size);
munmap(addr, size);
}
}
closedir(dir);
dir = opendir("/vendor/etc/selinux");
while ((entry = readdir(dir))) {
if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
continue;
if (strend(entry->d_name, ".cil") == 0) {
snprintf(path, sizeof(path), "/vendor/etc/selinux/%s", entry->d_name);
mmap_ro(path, &addr, &size);
cil_add_file(db, path, addr, size);
munmap(addr, size);
}
}
closedir(dir);
cil_compile(db);
cil_build_policydb(db, &pdb);
cil_db_destroy(&db);
policydb = &pdb->p;
}
// Magisk patches
sepol_min_rules();
dump_policydb("/sepolicy");
destroy_policydb();
}
int main(int argc, char *argv[]) {
umask(0);
struct cmdline cmd;
parse_cmdline(&cmd);
if (cmd.skip_initramfs) {
// Normal boot mode
// Clear rootfs
int root = open("/", O_RDONLY | O_CLOEXEC);
rm_rf(root);
mkdir("/sys", 0755);
mount("sysfs", "/sys", "sysfs", 0, NULL);
char partname[32];
snprintf(partname, sizeof(partname), "system%s", cmd.slot);
struct device dev;
setup_block(&dev, partname);
mkdir("/system_root", 0755);
mount(dev.path, "/system_root", "ext4", MS_RDONLY, NULL);
int system_root = open("/system_root", O_RDONLY | O_CLOEXEC);
clone_dir(system_root, root);
mount("/system_root/system", "/system", NULL, MS_BIND, NULL);
int overlay = open("/overlay", O_RDONLY | O_CLOEXEC);
if (overlay > 0)
mv_dir(overlay, root);
snprintf(partname, sizeof(partname), "vendor%s", cmd.slot);
// We need to mount independent vendor partition
if (setup_block(&dev, partname) == 0)
mount(dev.path, "/vendor", "ext4", MS_RDONLY, NULL);
patch_ramdisk();
patch_sepolicy();
close(root);
close(system_root);
close(overlay);
rmdir("/overlay");
umount("/vendor");
} else {
// Recovery mode
// Revert original init binary
unlink("/init");
rename("/.backup/init", "/init");
}
execv("/init", argv);
return 0;
}