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/*
* Copyright (C) 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "Access.h"
#include <android-base/logging.h>
#include <binder/IPCThreadState.h>
#include <log/log_safetynet.h>
#include <selinux/android.h>
#include <selinux/avc.h>
namespace android {
#ifdef VENDORSERVICEMANAGER
constexpr bool kIsVendor = true;
#else
constexpr bool kIsVendor = false;
#endif
static std::string getPidcon(pid_t pid) {
android_errorWriteLog(0x534e4554, "121035042");
char* lookup = nullptr;
if (getpidcon(pid, &lookup) < 0) {
LOG(ERROR) << "SELinux: getpidcon(pid=" << pid << ") failed to retrieve pid context";
return "";
}
std::string result = lookup;
freecon(lookup);
return result;
}
static struct selabel_handle* getSehandle() {
static struct selabel_handle* gSehandle = nullptr;
if (gSehandle != nullptr && selinux_status_updated()) {
selabel_close(gSehandle);
gSehandle = nullptr;
}
if (gSehandle == nullptr) {
gSehandle = kIsVendor
? selinux_android_vendor_service_context_handle()
: selinux_android_service_context_handle();
}
CHECK(gSehandle != nullptr);
return gSehandle;
}
struct AuditCallbackData {
const Access::CallingContext* context;
const std::string* tname;
};
static int auditCallback(void *data, security_class_t /*cls*/, char *buf, size_t len) {
const AuditCallbackData* ad = reinterpret_cast<AuditCallbackData*>(data);
if (!ad) {
LOG(ERROR) << "No service manager audit data";
return 0;
}
snprintf(buf, len, "pid=%d uid=%d name=%s", ad->context->debugPid, ad->context->uid,
ad->tname->c_str());
return 0;
}
Access::Access() {
union selinux_callback cb;
cb.func_audit = auditCallback;
selinux_set_callback(SELINUX_CB_AUDIT, cb);
cb.func_log = kIsVendor ? selinux_vendor_log_callback : selinux_log_callback;
selinux_set_callback(SELINUX_CB_LOG, cb);
CHECK(selinux_status_open(true /*fallback*/) >= 0);
CHECK(getcon(&mThisProcessContext) == 0);
}
Access::~Access() {
freecon(mThisProcessContext);
}
Access::CallingContext Access::getCallingContext() {
IPCThreadState* ipc = IPCThreadState::self();
const char* callingSid = ipc->getCallingSid();
pid_t callingPid = ipc->getCallingPid();
return CallingContext {
.debugPid = callingPid,
.uid = ipc->getCallingUid(),
.sid = callingSid ? std::string(callingSid) : getPidcon(callingPid),
};
}
bool Access::canFind(const CallingContext& ctx,const std::string& name) {
return actionAllowedFromLookup(ctx, name, "find");
}
bool Access::canAdd(const CallingContext& ctx, const std::string& name) {
return actionAllowedFromLookup(ctx, name, "add");
}
bool Access::canList(const CallingContext& ctx) {
return actionAllowed(ctx, mThisProcessContext, "list", "service_manager");
}
bool Access::actionAllowed(const CallingContext& sctx, const char* tctx, const char* perm,
const std::string& tname) {
const char* tclass = "service_manager";
AuditCallbackData data = {
.context = &sctx,
.tname = &tname,
};
return 0 == selinux_check_access(sctx.sid.c_str(), tctx, tclass, perm,
reinterpret_cast<void*>(&data));
}
bool Access::actionAllowedFromLookup(const CallingContext& sctx, const std::string& name, const char *perm) {
char *tctx = nullptr;
if (selabel_lookup(getSehandle(), &tctx, name.c_str(), SELABEL_CTX_ANDROID_SERVICE) != 0) {
LOG(ERROR) << "SELinux: No match for " << name << " in service_contexts.\n";
return false;
}
bool allowed = actionAllowed(sctx, tctx, perm, name);
freecon(tctx);
return allowed;
}
} // android
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