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Redesign of MagiskSU's sepolicy model

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Introduce new domain `magisk_client` and new file type `magisk_exec`.

Connection to magiskd's always-on socket is restricted to magisk_client
only. Whitelisted process domains can transit to magisk_client through
executing files labelled magisk_exec. The main magisk binary shall be
the only file labelled as magisk_exec throughout the whole system.
All processes thus are no longer allowed to connect to magiskd directly
without going through the proper magisk binary.

Connection failures are silenced from audit logs with dontaudit rules,
so crazy processes which traverse through all unix domain sockets to try
connection can no longer check logcat to know the actual reason behind
EACCES, leaking the denied process policy (which is u:r:magisk:s0).

This also allows us to remove many rules that open up holes in
untrusted_app domains that were used to make remote shell work properly.
Since all processes establishing the remote shell are now restricted to
the magisk_client domain, all these rules are moved to magisk_client.
This makes Magisk require fewer compromises in Android's security model.

Note: as of this commit, requesting new root access via Magisk Manager
will stop working as Magisk Manager can no longer communicate with
magiskd directly. This will be addressed in a future commit that
involves changes in both native and application side.
This commit is contained in:
topjohnwu 2020-06-03 23:29:42 -07:00
parent ae0dcabf43
commit ec3705f2ed
6 changed files with 88 additions and 58 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
native/jni/core/restorecon.cpp
View File

@ -10,7 +10,8 @@ using namespace std;
#define SYSTEM_CON "u:object_r:system_file:s0"
#define ADB_CON "u:object_r:adb_data_file:s0"
#define ROOT_CON "u:object_r:rootfs:s0"
#define MAGISK_CON "u:object_r:" SEPOL_FILE_DOMAIN ":s0"
#define MAGISK_CON "u:object_r:" SEPOL_FILE_TYPE ":s0"
#define EXEC_CON "u:object_r:" SEPOL_EXEC_TYPE ":s0"
static void restore_syscon(int dirfd) {
struct dirent *entry;
@ -86,9 +87,9 @@ void restore_tmpcon() {
int dfd = dirfd(dir.get());
for (dirent *entry; (entry = xreaddir(dir.get()));) {
if (entry->d_name == "magisk"sv || entry->d_name == "magiskinit"sv)
setfilecon_at(dfd, entry->d_name, MAGISK_CON);
if (entry->d_name == "magisk"sv)
setfilecon_at(dfd, entry->d_name, EXEC_CON);
else
setfilecon_at(dfd, entry->d_name, ROOT_CON);
setfilecon_at(dfd, entry->d_name, SYSTEM_CON);
}
}

2
native/jni/core/scripting.cpp
View File

@ -83,7 +83,7 @@ rm -f $APK
)EOF";
void install_apk(const char *apk) {
setfilecon(apk, "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon(apk, "u:object_r:" SEPOL_FILE_TYPE ":s0");
exec_t exec {
.pre_exec = set_standalone,
.fork = fork_no_zombie

120
native/jni/magiskpolicy/rules.cpp
View File

@ -1,33 +1,8 @@
#include <initializer_list>
#include <logging.hpp>
#include <magiskpolicy.hpp>
#include "sepolicy.hpp"
void sepol_impl::allow_su_client(const char *type) {
if (!exists(type))
return;
allow(type, SEPOL_PROC_DOMAIN, "unix_stream_socket", "connectto");
allow(type, SEPOL_PROC_DOMAIN, "unix_stream_socket", "getopt");
// Allow binder service
allow(type, SEPOL_PROC_DOMAIN, "binder", "call");
allow(type, SEPOL_PROC_DOMAIN, "binder", "transfer");
// Allow termios ioctl
allow(type, "devpts", "chr_file", "ioctl");
allow(type, "untrusted_app_devpts", "chr_file", "ioctl");
allow(type, "untrusted_app_25_devpts", "chr_file", "ioctl");
allow(type, "untrusted_app_all_devpts", "chr_file", "ioctl");
if (db->policyvers >= POLICYDB_VERSION_XPERMS_IOCTL) {
allowxperm(type, "devpts", "chr_file", "0x5400-0x54FF");
allowxperm(type, "untrusted_app_devpts", "chr_file", "0x5400-0x54FF");
allowxperm(type, "untrusted_app_25_devpts", "chr_file", "0x5400-0x54FF");
allowxperm(type, "untrusted_app_all_devpts", "chr_file", "0x5400-0x54FF");
}
}
void sepolicy::magisk_rules() {
// Temp suppress warnings
auto bak = log_cb.w;
@ -37,18 +12,86 @@ void sepolicy::magisk_rules() {
deny(ALL, "kernel", "security", "load_policy");
type(SEPOL_PROC_DOMAIN, "domain");
type(SEPOL_FILE_DOMAIN, "file_type");
permissive(SEPOL_PROC_DOMAIN);
type(SEPOL_CLIENT_DOMAIN, "domain");
type(SEPOL_FILE_TYPE, "file_type");
type(SEPOL_EXEC_TYPE, "file_type");
permissive(SEPOL_PROC_DOMAIN); /* Just in case something is missing */
typeattribute(SEPOL_PROC_DOMAIN, "mlstrustedsubject");
typeattribute(SEPOL_PROC_DOMAIN, "netdomain");
typeattribute(SEPOL_PROC_DOMAIN, "bluetoothdomain");
typeattribute(SEPOL_FILE_DOMAIN, "mlstrustedobject");
typeattribute(SEPOL_FILE_TYPE, "mlstrustedobject");
// Make our root domain unconstrained
allow(SEPOL_PROC_DOMAIN, ALL, ALL, ALL);
// Allow us to do any ioctl on all block devices
if (db->policyvers >= POLICYDB_VERSION_XPERMS_IOCTL)
allowxperm(SEPOL_PROC_DOMAIN, ALL, "blk_file", ALL);
// Create unconstrained file type
allow(ALL, SEPOL_FILE_TYPE, "file", ALL);
allow(ALL, SEPOL_FILE_TYPE, "dir", ALL);
allow(ALL, SEPOL_FILE_TYPE, "fifo_file", ALL);
allow(ALL, SEPOL_FILE_TYPE, "chr_file", ALL);
// Basic su client needs
allow(SEPOL_CLIENT_DOMAIN, ALL, "fd", "use");
allow(SEPOL_CLIENT_DOMAIN, SEPOL_CLIENT_DOMAIN, ALL, ALL);
allow(SEPOL_CLIENT_DOMAIN, SEPOL_EXEC_TYPE, "file", ALL);
allow(SEPOL_CLIENT_DOMAIN, SEPOL_PROC_DOMAIN, "unix_stream_socket", "connectto");
allow(SEPOL_CLIENT_DOMAIN, SEPOL_PROC_DOMAIN, "unix_stream_socket", "getopt");
// Allow su client to manipulate pts
const char *pts[] {
"devpts", "untrusted_app_devpts", "untrusted_app_25_devpts", "untrusted_app_all_devpts" };
for (auto type : pts) {
allow(SEPOL_CLIENT_DOMAIN, type, "chr_file", "read");
allow(SEPOL_CLIENT_DOMAIN, type, "chr_file", "write");
allow(SEPOL_CLIENT_DOMAIN, type, "chr_file", "getattr");
allow(SEPOL_CLIENT_DOMAIN, type, "chr_file", "ioctl");
if (db->policyvers >= POLICYDB_VERSION_XPERMS_IOCTL)
allowxperm(SEPOL_CLIENT_DOMAIN, type, "chr_file", "0x5400-0x54FF");
}
// Allow these processes to access MagiskSU
const char *clients[] {
"init", "shell", "system_app", "priv_app", "platform_app", "untrusted_app",
"untrusted_app_25", "untrusted_app_27", "untrusted_app_29", "update_engine" };
for (auto type : clients) {
if (!exists(type))
continue;
// exec magisk
allow(type, SEPOL_EXEC_TYPE, "file", "read");
allow(type, SEPOL_EXEC_TYPE, "file", "open");
allow(type, SEPOL_EXEC_TYPE, "file", "getattr");
allow(type, SEPOL_EXEC_TYPE, "file", "execute");
// Auto transit to client domain
type_transition(type, SEPOL_EXEC_TYPE, "process", SEPOL_CLIENT_DOMAIN);
allow(type, SEPOL_CLIENT_DOMAIN, "process", "transition");
dontaudit(type, SEPOL_CLIENT_DOMAIN, "process", "siginh");
dontaudit(type, SEPOL_CLIENT_DOMAIN, "process", "rlimitinh");
dontaudit(type, SEPOL_CLIENT_DOMAIN, "process", "noatsecure");
allow(SEPOL_CLIENT_DOMAIN, type, "process", "sigchld");
allow(SEPOL_CLIENT_DOMAIN, type, "fifo_file", "read");
allow(SEPOL_CLIENT_DOMAIN, type, "fifo_file", "write");
allow(SEPOL_CLIENT_DOMAIN, type, "fifo_file", "ioctl");
}
// Allow system_server to manage magisk_client
allow("system_server", SEPOL_CLIENT_DOMAIN, "process", "getpgid");
allow("system_server", SEPOL_CLIENT_DOMAIN, "process", "sigkill");
// Don't allow pesky processes to monitor audit deny logs when poking magisk daemon sockets
dontaudit(ALL, SEPOL_PROC_DOMAIN, "unix_stream_socket", ALL);
// Let everyone access tmpfs files (for SAR sbin overlay)
allow(ALL, "tmpfs", "file", ALL);
// For normal rootfs file/directory operations when rw (for SAR / overlay)
// For relabelling files
allow("rootfs", "labeledfs", "filesystem", "associate");
allow(SEPOL_FILE_TYPE, "pipefs", "filesystem", "associate");
allow(SEPOL_FILE_TYPE, "devpts", "filesystem", "associate");
// Let init transit to SEPOL_PROC_DOMAIN
allow("kernel", "kernel", "process", "setcurrent");
@ -60,25 +103,6 @@ void sepolicy::magisk_rules() {
allow("init", "tmpfs", "file", "getattr");
allow("init", "tmpfs", "file", "execute");
// Make our domain unconstrained
allow(SEPOL_PROC_DOMAIN, ALL, ALL, ALL);
// Allow us to do any ioctl on all block devices
if (db->policyvers >= POLICYDB_VERSION_XPERMS_IOCTL)
allowxperm(SEPOL_PROC_DOMAIN, ALL, "blk_file", ALL);
// Make our file type unconstrained
allow(ALL, SEPOL_FILE_DOMAIN, "file", ALL);
allow(ALL, SEPOL_FILE_DOMAIN, "dir", ALL);
allow(ALL, SEPOL_FILE_DOMAIN, "fifo_file", ALL);
allow(ALL, SEPOL_FILE_DOMAIN, "chr_file", ALL);
// Allow these processes to access MagiskSU
std::initializer_list<const char *> clients {
"init", "shell", "system_app", "priv_app", "platform_app", "untrusted_app",
"untrusted_app_25", "untrusted_app_27", "untrusted_app_29", "update_engine" };
for (auto type : clients)
impl->allow_su_client(type);
// suRights
allow("servicemanager", SEPOL_PROC_DOMAIN, "dir", "search");
allow("servicemanager", SEPOL_PROC_DOMAIN, "dir", "read");

1
native/jni/magiskpolicy/sepolicy.hpp
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@ -20,7 +20,6 @@ struct sepol_impl : public sepolicy {
void add_typeattribute(type_datum_t *type, type_datum_t *attr);
bool add_typeattribute(const char *type, const char *attr);
void strip_dontaudit();
void allow_su_client(const char *type);
};
#define impl static_cast<sepol_impl *>(this)

6
native/jni/su/su_daemon.cpp
View File

@ -275,9 +275,9 @@ void su_daemon_handler(int client, struct ucred *credential) {
xdup2(errfd, STDERR_FILENO);
// Unleash all streams from SELinux hell
setfilecon("/proc/self/fd/0", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/proc/self/fd/1", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/proc/self/fd/2", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/proc/self/fd/0", "u:object_r:" SEPOL_FILE_TYPE ":s0");
setfilecon("/proc/self/fd/1", "u:object_r:" SEPOL_FILE_TYPE ":s0");
setfilecon("/proc/self/fd/2", "u:object_r:" SEPOL_FILE_TYPE ":s0");
close(infd);
close(outfd);

8
native/jni/utils/include/selinux.hpp
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@ -16,8 +16,14 @@
#define SYSEXT_POLICY_DIR "/system_ext/etc/selinux/"
#define SPLIT_PLAT_CIL PLAT_POLICY_DIR "plat_sepolicy.cil"
// Unconstrained domain the daemon and root processes run in
#define SEPOL_PROC_DOMAIN "magisk"
#define SEPOL_FILE_DOMAIN "magisk_file"
// Highly constrained domain, sole purpose is to connect to daemon
#define SEPOL_CLIENT_DOMAIN "magisk_client"
// Unconstrained file type that anyone can access
#define SEPOL_FILE_TYPE "magisk_file"
// Special file type to allow clients to transit to client domain automatically
#define SEPOL_EXEC_TYPE "magisk_exec"
extern void (*freecon)(char *con);
extern int (*setcon)(const char *con);