Introduce magiskinit for Pixel (XL)

jni/Android.mk

@@ -74,6 +74,15 @@ LOCAL_SRC_FILES := \
 LOCAL_CFLAGS := -DZLIB_CONST
 include $(BUILD_EXECUTABLE)
 
+# magiskinit
+ifeq ($(TARGET_ARCH_ABI), arm64-v8a)
+include $(CLEAR_VARS)
+LOCAL_MODULE := magiskinit
+LOCAL_SRC_FILES := magiskinit.c
+LOCAL_LDFLAGS := -static
+include $(BUILD_EXECUTABLE)
+endif
+
 # 32-bit static binaries
 ifneq ($(TARGET_ARCH_ABI), x86_64)
 ifneq ($(TARGET_ARCH_ABI), arm64-v8a)

jni/magiskinit.c

@@ -0,0 +1,205 @@
+#include <stdio.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/sendfile.h>
+#include <sys/sysmacros.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];
+};
+
+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 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:
+			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];
+	mkdir("/sys", 0755);
+	mount("sysfs", "/sys", "sysfs", 0, NULL);
+	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;
+}
+
+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);
+
+		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);
+
+		close(root);
+		close(system_root);
+	} else {
+		// Recovery mode
+		// Revert original init binary
+		unlink("/init");
+		rename("/init_orig", "/init");
+	}
+
+	execv("/init", argv);
+
+	return 0;
+}