Magisk/jni/core/magiskinit.c

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/* magiskinit.c - 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>
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#include <lzma.h>
#include <cil/cil.h>
#include "magisk.h"
#include "utils.h"
#include "magiskpolicy.h"
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#include "magiskrc.h"
#include "dump.h"
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// #define VLOG(fmt, ...) printf(fmt, __VA_ARGS__) /* Enable to debug */
#define VLOG(fmt, ...)
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;
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);
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} else if (strncmp(tok, "androidboot.slot", 16) == 0) {
cmd->slot[0] = '_';
sscanf(tok, "androidboot.slot=%s", cmd->slot + 1);
} else if (strcmp(tok, "skip_initramfs") == 0) {
cmd->skip_initramfs = 1;
}
tok = strtok(NULL, " ");
}
}
static void parse_device(struct device *dev, char *uevent) {
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dev->partname[0] = '\0';
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");
}
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VLOG("%s [%s] (%u, %u)\n", dev->devname, dev->partname, (unsigned) dev->major, (unsigned) dev->minor);
}
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_init_rc(char *data, uint32_t *size) {
int injected = 0;
char *new_data = malloc(*size + 23);
char *old_data = data;
uint32_t pos = 0;
for (char *tok = strsep(&old_data, "\n"); tok; tok = strsep(&old_data, "\n")) {
if (!injected && strncmp(tok, "import", 6) == 0) {
if (strstr(tok, "init.magisk.rc")) {
injected = 1;
} else {
strcpy(new_data + pos, "import /init.magisk.rc\n");
pos += 23;
injected = 1;
}
} else if (strstr(tok, "selinux.reload_policy")) {
continue;
}
// Copy the line
strcpy(new_data + pos, tok);
pos += strlen(tok);
new_data[pos++] = '\n';
}
*size = pos;
return new_data;
}
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 int compile_cil() {
DIR *dir;
struct dirent *entry;
char path[128];
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);
// plat
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);
// mapping
char plat[10];
int fd = open("/vendor/etc/selinux/plat_sepolicy_vers.txt", O_RDONLY | O_CLOEXEC);
if (fd > 0) {
plat[read(fd, plat, sizeof(plat)) - 1] = '\0';
snprintf(path, sizeof(path), "/system/etc/selinux/mapping/%s.cil", plat);
mmap_ro(path, &addr, &size);
cil_add_file(db, path, addr, size);
munmap(addr, size);
close(fd);
}
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;
return 0;
}
static int verify_precompiled() {
DIR *dir;
struct dirent *entry;
int fd;
char sys_sha[70], ven_sha[70];
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, ".sha256") == 0) {
fd = openat(dirfd(dir), entry->d_name, O_RDONLY | O_CLOEXEC);
ven_sha[read(fd, ven_sha, sizeof(ven_sha))] = '\0';
close(fd);
break;
}
}
closedir(dir);
dir = opendir("/system/etc/selinux");
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);
sys_sha[read(fd, sys_sha, sizeof(sys_sha))] = '\0';
close(fd);
break;
}
}
closedir(dir);
return strcmp(sys_sha, ven_sha);
}
static void patch_sepolicy() {
if (access("/sepolicy", R_OK) == 0) {
load_policydb("/sepolicy");
} else if (access("/vendor/etc/selinux/precompiled_sepolicy", R_OK) == 0
&& verify_precompiled() == 0) {
load_policydb("/vendor/etc/selinux/precompiled_sepolicy");
} else if (access("/system/etc/selinux/plat_sepolicy.cil", R_OK) == 0) {
compile_cil();
}
sepol_med_rules();
dump_policydb("/sepolicy");
}
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#define BUFSIZE (1 << 20)
static int unxz(const void *buf, size_t size, int fd) {
lzma_stream strm = LZMA_STREAM_INIT;
if (lzma_auto_decoder(&strm, UINT64_MAX, 0) != LZMA_OK)
return 1;
lzma_ret ret = 0;
void *out = malloc(BUFSIZE);
strm.next_in = buf;
strm.avail_in = size;
do {
strm.next_out = out;
strm.avail_out = BUFSIZE;
ret = lzma_code(&strm, LZMA_RUN);
write(fd, out, BUFSIZE - strm.avail_out);
} while (strm.avail_out == 0 && ret == LZMA_OK);
free(out);
lzma_end(&strm);
if (ret != LZMA_OK && ret != LZMA_STREAM_END)
return 1;
return 0;
}
static int dump_magisk(const char *path, mode_t mode) {
unlink(path);
int fd = creat(path, mode);
int ret = unxz(magisk_dump, sizeof(magisk_dump), fd);
close(fd);
return ret;
}
static int dump_magiskrc(const char *path, mode_t mode) {
int fd = creat(path, mode);
write(fd, magiskrc, sizeof(magiskrc));
close(fd);
return 0;
}
int main(int argc, char *argv[]) {
if (strcmp(basename(argv[0]), "magiskpolicy") == 0 || strcmp(basename(argv[0]), "supolicy") == 0)
return magiskpolicy_main(argc, argv);
if (argc > 1 && (strcmp(argv[1], "magiskpolicy") == 0 || strcmp(argv[1], "supolicy") == 0))
return magiskpolicy_main(argc - 1, argv + 1);
umask(0);
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if (argc > 1) {
if (strcmp(argv[2], "magisk") == 0)
return dump_magisk(argv[3], 0755);
else if (strcmp(argv[2], "magiskrc") == 0)
return dump_magiskrc(argv[3], 0755);
}
// Extract and link files
mkdir("/overlay", 0000);
dump_magiskrc("/overlay/init.magisk.rc", 0750);
mkdir("/overlay/sbin", 0755);
dump_magisk("/overlay/sbin/magisk", 0755);
mkdir("/overlay/root", 0755);
link("/init", "/overlay/root/magiskinit");
symlink("/root/magiskinit", "/overlay/root/magiskpolicy");
symlink("/root/magiskinit", "/overlay/root/supolicy");
struct cmdline cmd;
parse_cmdline(&cmd);
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VLOG("cmdline: skip_initramfs=[%d] slot_suffix=[%s]\n", cmd.skip_initramfs, cmd.slot);
int root = open("/", O_RDONLY | O_CLOEXEC);
if (cmd.skip_initramfs) {
// Exclude overlay folder
excl_list = (char *[]) { "overlay", ".backup", NULL };
// Clear rootfs
frm_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);
// Exclude system folder
excl_list = (char *[]) { "system", NULL };
clone_dir(system_root, root);
mkdir("/system", 0755);
mount("/system_root/system", "/system", NULL, MS_BIND, NULL);
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);
close(system_root);
} else {
// Revert original init binary
unlink("/init");
link("/.backup/init", "/init");
}
int overlay = open("/overlay", O_RDONLY | O_CLOEXEC);
mv_dir(overlay, root);
patch_ramdisk();
patch_sepolicy();
// Clean up
rmdir("/overlay");
umount("/vendor");
close(overlay);
close(root);
if (fork() == 0) {
// Fork a new process for full patch
setsid();
sepol_allow("su", ALL, ALL, ALL);
while (access(SELINUX_LOAD, W_OK) == -1) {
usleep(500); /* Wait 0.5ms */
}
dump_policydb(SELINUX_LOAD);
close(open(PATCHDONE, O_RDONLY | O_CREAT, 0));
destroy_policydb();
} else {
// Finally, give control back!
execv("/init", argv);
}
return 0;
}