Magisk/native/jni/utils/selinux.cpp

#include <sys/xattr.h>

#include <utils.hpp>
#include <selinux.hpp>

using namespace std;

// Stub implementation

static int stub(const char *) { return 0; }

static int stub(const char *, const char *) { return 0; }

static int stub(const char *, char **ctx) {
	*ctx = strdup("");
	return 0;
}

static int stub(int, const char *) { return 0; }

static int stub(int, char **ctx) {
	*ctx = strdup("");
	return 0;
}

// Builtin implementation

static void __freecon(char *s) {
	free(s);
}

static int __setcon(const char *ctx) {
	int fd = open("/proc/self/attr/current", O_WRONLY | O_CLOEXEC);
	if (fd < 0)
		return fd;
	size_t len = strlen(ctx) + 1;
	int rc = write(fd, ctx, len);
	close(fd);
	return rc != len;
}

static int __getfilecon(const char *path, char **ctx) {
	char buf[1024];
	int rc = syscall(__NR_getxattr, path, XATTR_NAME_SELINUX, buf, sizeof(buf) - 1);
	if (rc >= 0)
		*ctx = strdup(buf);
	return rc;
}

static int __lgetfilecon(const char *path, char **ctx) {
	char buf[1024];
	int rc = syscall(__NR_lgetxattr, path, XATTR_NAME_SELINUX, buf, sizeof(buf) - 1);
	if (rc >= 0)
		*ctx = strdup(buf);
	return rc;
}

static int __fgetfilecon(int fd, char **ctx) {
	char buf[1024];
	int rc = syscall(__NR_fgetxattr, fd, XATTR_NAME_SELINUX, buf, sizeof(buf) - 1);
	if (rc >= 0)
		*ctx = strdup(buf);
	return rc;
}

static int __setfilecon(const char *path, const char *ctx) {
	return syscall(__NR_setxattr, path, XATTR_NAME_SELINUX, ctx, strlen(ctx) + 1, 0);
}

static int __lsetfilecon(const char *path, const char *ctx) {
	return syscall(__NR_lsetxattr, path, XATTR_NAME_SELINUX, ctx, strlen(ctx) + 1, 0);
}

static int __fsetfilecon(int fd, const char *ctx) {
	return syscall(__NR_fsetxattr, fd, XATTR_NAME_SELINUX, ctx, strlen(ctx) + 1, 0);
}

// Function pointers

void (*freecon)(char *) = __freecon;
int (*setcon)(const char *) = stub;
int (*getfilecon)(const char *, char **) = stub;
int (*lgetfilecon)(const char *, char **) = stub;
int (*fgetfilecon)(int, char **) = stub;
int (*setfilecon)(const char *, const char *) = stub;
int (*lsetfilecon)(const char *, const char *) = stub;
int (*fsetfilecon)(int, const char *) = stub;

void getfilecon_at(int dirfd, const char *name, char **con) {
	char path[4096];
	fd_pathat(dirfd, name, path, sizeof(path));
	if (lgetfilecon(path, con))
		*con = strdup("");
}

void setfilecon_at(int dirfd, const char *name, const char *con) {
	char path[4096];
	fd_pathat(dirfd, name, path, sizeof(path));
	lsetfilecon(path, con);
}

void selinux_builtin_impl() {
	setcon = __setcon;
	getfilecon = __getfilecon;
	lgetfilecon = __lgetfilecon;
	fgetfilecon = __fgetfilecon;
	setfilecon = __setfilecon;
	lsetfilecon = __lsetfilecon;
	fsetfilecon = __fsetfilecon;
}

void dload_selinux() {
	if (access("/system/lib/libselinux.so", F_OK))
		return;
	/* We only check whether libselinux.so exists but don't dlopen.
	 * For some reason calling symbols returned from dlsym
	 * will result to SEGV_ACCERR on some devices.
	 * Always use builtin implementations for SELinux stuffs. */
	selinux_builtin_impl();
}