Is it possible to use C++ Binder API to communicate between two non-privileged processes?
All examples I found (e.g. https://github.com/mcr/Android-HelloWorldService) rely on registering service via ServiceManager->addService()
which throws following error when executing on a non-rooted phone:
E/ServiceManager﹕ add_service('my.test.service',0x48) uid=2000 - PERMISSION DENIED
Inside the AOSP (Android Open Source Project) in the file frameworks/native/cmds/servicemanager/service_manager.c
you can find the following method:
int svc_can_register(uid_t uid, const uint16_t *name)
{
size_t n;
if ((uid == 0) || (uid == AID_SYSTEM))
return 1;
for (n = 0; n < sizeof(allowed) / sizeof(allowed[0]); n++)
if ((uid == allowed[n].uid) && str16eq(name, allowed[n].name))
return 1;
return 0;
}
and a bit above:
/* TODO:
* These should come from a config file or perhaps be
* based on some namespace rules of some sort (media
* uid can register media.*, etc)
*/
static struct {
uid_t uid;
const char *name;
} allowed[] = {
{ AID_MEDIA, "media.audio_flinger" },
{ AID_MEDIA, "media.log" },
{ AID_MEDIA, "media.player" },
{ AID_MEDIA, "media.camera" },
{ AID_MEDIA, "media.audio_policy" },
{ AID_DRM, "drm.drmManager" },
{ AID_NFC, "nfc" },
{ AID_BLUETOOTH, "bluetooth" },
{ AID_RADIO, "radio.phone" },
{ AID_RADIO, "radio.sms" },
{ AID_RADIO, "radio.phonesubinfo" },
{ AID_RADIO, "radio.simphonebook" },
/* TODO: remove after phone services are updated: */
{ AID_RADIO, "phone" },
{ AID_RADIO, "sip" },
{ AID_RADIO, "isms" },
{ AID_RADIO, "iphonesubinfo" },
{ AID_RADIO, "simphonebook" },
{ AID_MEDIA, "common_time.clock" },
{ AID_MEDIA, "common_time.config" },
{ AID_KEYSTORE, "android.security.keystore" },
};
and further down:
if (!svc_can_register(uid, s)) {
ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
str8(s), handle, uid);
return -1;
}
Conclusion: the system binary in /system/bin/servicemanager doesn't allow it. (for security reasons)
Possible solutions:
- kill and reuse PID and name of service listed
- recompile your own servicemanager binary and use this one
- inject your code in this binary, to allow everyone
- change the PID servicemanager reads (change the ioctl response servicemanager gets in binder.h (same directory))
- or just start your server in a binary having root permissions. Clients can connect without root, but the server needs it.