sandboxed-api/sandboxed_api/client.cc

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// Copyright 2019 Google LLC
//
// 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 "sandboxed_api/sandbox2/client.h"
#include <dlfcn.h>
#include <sys/syscall.h>
#include <cstring>
#include <iterator>
#include <list>
#include <vector>
#include <glog/logging.h>
#include "google/protobuf/descriptor.h"
#include "google/protobuf/message.h"
#include "absl/base/dynamic_annotations.h"
#include "sandboxed_api/util/flag.h"
#include "absl/strings/str_cat.h"
#include "sandboxed_api/call.h"
#include "sandboxed_api/config.h"
#include "sandboxed_api/lenval_core.h"
#include "sandboxed_api/proto_arg.pb.h"
#include "sandboxed_api/sandbox2/comms.h"
#include "sandboxed_api/sandbox2/forkingclient.h"
#include "sandboxed_api/sandbox2/logsink.h"
#include "sandboxed_api/vars.h"
#include <ffi.h>
#include <ffitarget.h>
namespace sapi {
namespace {
// Guess the FFI type on the basis of data size and float/non-float/bool.
ffi_type* GetFFIType(size_t size, v::Type type) {
switch (type) {
case v::Type::kVoid:
return &ffi_type_void;
case v::Type::kPointer:
return &ffi_type_pointer;
case v::Type::kFd:
return &ffi_type_sint;
case v::Type::kFloat:
if (size == sizeof(float)) {
return &ffi_type_float;
} else if (size == sizeof(double)) {
return &ffi_type_double;
} else if (size == sizeof(long double)) {
return &ffi_type_longdouble;
} else {
LOG(FATAL) << "Unknown floating-point size: " << size;
}
case v::Type::kInt:
switch (size) {
case 1:
return &ffi_type_uint8;
case 2:
return &ffi_type_uint16;
case 4:
return &ffi_type_uint32;
case 8:
return &ffi_type_uint64;
default:
LOG(FATAL) << "Unknown integral size: " << size;
}
case v::Type::kStruct:
LOG(FATAL) << "Structs are not supported as function arguments";
case v::Type::kProto:
LOG(FATAL) << "Protos are not supported as function arguments";
default:
LOG(FATAL) << "Unknown type: " << type << " of size: " << size;
}
}
// Provides an interface to prepare the arguments for a function call.
// In case of protobuf arguments, the class allocates and manages
// memory for the deserialized protobuf.
class FunctionCallPreparer {
public:
explicit FunctionCallPreparer(const FuncCall& call) {
CHECK(call.argc <= FuncCall::kArgsMax)
<< "Number of arguments of a sandbox call exceeds limits.";
for (int i = 0; i < call.argc; ++i) {
arg_types_[i] = GetFFIType(call.arg_size[i], call.arg_type[i]);
}
ret_type_ = GetFFIType(call.ret_size, call.ret_type);
for (int i = 0; i < call.argc; ++i) {
if (call.arg_type[i] == v::Type::kPointer &&
call.aux_type[i] == v::Type::kProto) {
// Deserialize protobuf stored in the LenValueStruct and keep a
// reference to both. This way we are able to update the content of the
// LenValueStruct (when the sandboxee modifies the protobuf).
// This will also make sure that the protobuf is freed afterwards.
arg_values_[i] = GetDeserializedProto(
reinterpret_cast<LenValStruct*>(call.args[i].arg_int));
} else if (call.arg_type[i] == v::Type::kFloat) {
arg_values_[i] = reinterpret_cast<const void*>(&call.args[i].arg_float);
} else {
arg_values_[i] = reinterpret_cast<const void*>(&call.args[i].arg_int);
}
}
}
~FunctionCallPreparer() {
for (const auto& idx_proto : protos_to_be_destroyed_) {
const auto proto = idx_proto.second;
LenValStruct* lvs = idx_proto.first;
// There is no way to figure out whether the protobuf structure has
// changed or not, so we always serialize the protobuf again and replace
// the LenValStruct content.
std::vector<uint8_t> serialized = SerializeProto(*proto).value();
// Reallocate the LV memory to match its length.
if (lvs->size != serialized.size()) {
void* newdata = realloc(lvs->data, serialized.size());
if (!newdata) {
LOG(FATAL) << "Failed to reallocate protobuf buffer (size="
<< serialized.size() << ")";
}
lvs->size = serialized.size();
lvs->data = newdata;
}
memcpy(lvs->data, serialized.data(), serialized.size());
delete proto;
}
}
ffi_type* ret_type() const { return ret_type_; }
ffi_type** arg_types() const { return const_cast<ffi_type**>(arg_types_); }
void** arg_values() const { return const_cast<void**>(arg_values_); }
private:
// Deserializes the protobuf argument.
google::protobuf::Message** GetDeserializedProto(LenValStruct* src) {
ProtoArg proto_arg;
if (!proto_arg.ParseFromArray(src->data, src->size)) {
LOG(FATAL) << "Unable to parse ProtoArg.";
}
const google::protobuf::Descriptor* desc =
google::protobuf::DescriptorPool::generated_pool()->FindMessageTypeByName(
proto_arg.full_name());
LOG_IF(FATAL, desc == nullptr) << "Unable to find the descriptor for '"
<< proto_arg.full_name() << "'" << desc;
google::protobuf::Message* deserialized_proto =
google::protobuf::MessageFactory::generated_factory()->GetPrototype(desc)->New();
LOG_IF(FATAL, deserialized_proto == nullptr)
<< "Unable to create deserialized proto for " << proto_arg.full_name();
if (!deserialized_proto->ParseFromString(proto_arg.protobuf_data())) {
LOG(FATAL) << "Unable to deserialized proto for "
<< proto_arg.full_name();
}
protos_to_be_destroyed_.push_back({src, deserialized_proto});
return &protos_to_be_destroyed_.back().second;
}
// Use list instead of vector to preserve references even with modifications.
// Contains pairs of lenval message pointer -> deserialized message
// so that we can serialize the argument again after the function call.
std::list<std::pair<LenValStruct*, google::protobuf::Message*>> protos_to_be_destroyed_;
ffi_type* ret_type_;
ffi_type* arg_types_[FuncCall::kArgsMax];
const void* arg_values_[FuncCall::kArgsMax];
};
} // namespace
namespace client {
// Error codes in the client code:
enum class Error : uintptr_t {
kUnset = 0,
kDlOpen,
kDlSym,
kCall,
};
// Handles requests to make function calls.
void HandleCallMsg(const FuncCall& call, FuncRet* ret) {
VLOG(1) << "HandleMsgCall, func: '" << call.func
<< "', # of args: " << call.argc;
ret->ret_type = call.ret_type;
void* handle = dlopen(nullptr, RTLD_NOW);
if (handle == nullptr) {
LOG(ERROR) << "dlopen(nullptr, RTLD_NOW)";
ret->success = false;
ret->int_val = static_cast<uintptr_t>(Error::kDlOpen);
return;
}
auto f = dlsym(handle, call.func);
if (f == nullptr) {
LOG(ERROR) << "Function '" << call.func << "' not found";
ret->success = false;
ret->int_val = static_cast<uintptr_t>(Error::kDlSym);
return;
}
FunctionCallPreparer arg_prep(call);
ffi_cif cif;
if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, call.argc, arg_prep.ret_type(),
arg_prep.arg_types()) != FFI_OK) {
ret->success = false;
ret->int_val = static_cast<uintptr_t>(Error::kCall);
return;
}
if (ret->ret_type == v::Type::kFloat) {
ffi_call(&cif, FFI_FN(f), &ret->float_val, arg_prep.arg_values());
} else {
ffi_call(&cif, FFI_FN(f), &ret->int_val, arg_prep.arg_values());
}
ret->success = true;
}
// Handles requests to allocate memory inside the sandboxee.
void HandleAllocMsg(const size_t size, FuncRet* ret) {
VLOG(1) << "HandleAllocMsg: size=" << size;
const void* allocated = malloc(size);
// Memory is copied to the pointer using an API that the memory sanitizer
// is blind to (process_vm_writev). Mark the memory as initialized here, so
// that the sandboxed code can still be tested using MSAN.
ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(allocated, size);
ret->ret_type = v::Type::kPointer;
ret->int_val = reinterpret_cast<uintptr_t>(allocated);
ret->success = true;
}
// Like HandleAllocMsg(), but handles requests to reallocate memory.
void HandleReallocMsg(uintptr_t ptr, size_t size, FuncRet* ret) {
VLOG(1) << "HandleReallocMsg(" << absl::StrCat(absl::Hex(ptr)) << ", " << size
<< ")";
const void* reallocated = realloc(reinterpret_cast<void*>(ptr), size);
// Memory is copied to the pointer using an API that the memory sanitizer
// is blind to (process_vm_writev). Mark the memory as initialized here, so
// that the sandboxed code can still be tested using MSAN.
ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(reallocated, size);
ret->ret_type = v::Type::kPointer;
ret->int_val = reinterpret_cast<uintptr_t>(reallocated);
ret->success = true;
}
// Handles requests to free memory previously allocated by HandleAllocMsg() and
// HandleReallocMsg().
void HandleFreeMsg(uintptr_t ptr, FuncRet* ret) {
VLOG(1) << "HandleFreeMsg: free(0x" << absl::StrCat(absl::Hex(ptr)) << ")";
free(reinterpret_cast<void*>(ptr));
ret->ret_type = v::Type::kVoid;
ret->success = true;
ret->int_val = 0ULL;
}
// Handles requests to find a symbol value.
void HandleSymbolMsg(const char* symname, FuncRet* ret) {
ret->ret_type = v::Type::kPointer;
void* handle = dlopen(nullptr, RTLD_NOW);
if (handle == nullptr) {
ret->success = false;
ret->int_val = static_cast<uintptr_t>(Error::kDlOpen);
return;
}
ret->int_val = reinterpret_cast<uintptr_t>(dlsym(handle, symname));
ret->success = true;
}
// Handles requests to receive a file descriptor from sandboxer.
void HandleSendFd(sandbox2::Comms* comms, FuncRet* ret) {
ret->ret_type = v::Type::kInt;
int fd = -1;
if (comms->RecvFD(&fd) == false) {
ret->success = false;
return;
}
ret->int_val = fd;
ret->success = true;
}
// Handles requests to send a file descriptor back to sandboxer.
void HandleRecvFd(sandbox2::Comms* comms, int fd_to_transfer, FuncRet* ret) {
ret->ret_type = v::Type::kVoid;
if (comms->SendFD(fd_to_transfer) == false) {
ret->success = false;
return;
}
ret->success = true;
}
// Handles requests to close a file descriptor in the sandboxee.
void HandleCloseFd(sandbox2::Comms* comms, int fd_to_close, FuncRet* ret) {
VLOG(1) << "HandleCloseFd: close(" << fd_to_close << ")";
close(fd_to_close);
ret->ret_type = v::Type::kVoid;
ret->success = true;
}
void HandleStrlen(sandbox2::Comms* comms, const char* ptr, FuncRet* ret) {
ret->ret_type = v::Type::kInt;
ret->int_val = strlen(ptr);
ret->success = true;
}
template <typename T>
static T BytesAs(const std::vector<uint8_t>& bytes) {
static_assert(std::is_trivial<T>(),
"only trivial types can be used with BytesAs");
CHECK_EQ(bytes.size(), sizeof(T));
T rv;
memcpy(&rv, bytes.data(), sizeof(T));
return rv;
}
void ServeRequest(sandbox2::Comms* comms) {
uint32_t tag;
std::vector<uint8_t> bytes;
CHECK(comms->RecvTLV(&tag, &bytes));
FuncRet ret{}; // Brace-init zeroes struct padding
switch (tag) {
case comms::kMsgCall:
VLOG(1) << "Client::kMsgCall";
HandleCallMsg(BytesAs<FuncCall>(bytes), &ret);
break;
case comms::kMsgAllocate:
VLOG(1) << "Client::kMsgAllocate";
HandleAllocMsg(BytesAs<size_t>(bytes), &ret);
break;
case comms::kMsgReallocate:
VLOG(1) << "Client::kMsgReallocate";
{
auto req = BytesAs<comms::ReallocRequest>(bytes);
HandleReallocMsg(req.old_addr, req.size, &ret);
}
break;
case comms::kMsgFree:
VLOG(1) << "Client::kMsgFree";
HandleFreeMsg(BytesAs<uintptr_t>(bytes), &ret);
break;
case comms::kMsgSymbol:
CHECK_EQ(bytes.size(),
1 + std::distance(bytes.begin(),
std::find(bytes.begin(), bytes.end(), '\0')));
VLOG(1) << "Received Client::kMsgSymbol message";
HandleSymbolMsg(reinterpret_cast<const char*>(bytes.data()), &ret);
break;
case comms::kMsgExit:
VLOG(1) << "Received Client::kMsgExit message";
syscall(__NR_exit_group, 0UL);
break;
case comms::kMsgSendFd:
VLOG(1) << "Received Client::kMsgSendFd message";
HandleSendFd(comms, &ret);
break;
case comms::kMsgRecvFd:
VLOG(1) << "Received Client::kMsgRecvFd message";
HandleRecvFd(comms, BytesAs<int>(bytes), &ret);
break;
case comms::kMsgClose:
VLOG(1) << "Received Client::kMsgClose message";
HandleCloseFd(comms, BytesAs<int>(bytes), &ret);
break;
case comms::kMsgStrlen:
VLOG(1) << "Received Client::kMsgStrlen message";
HandleStrlen(comms, BytesAs<const char*>(bytes), &ret);
break;
break;
default:
LOG(FATAL) << "Received unknown tag: " << tag;
break; // Not reached
}
if (ret.ret_type == v::Type::kFloat) {
VLOG(1) << "Returned value: " << ret.float_val
<< ", Success: " << (ret.success ? "Yes" : "No");
} else {
VLOG(1) << "Returned value: " << ret.int_val << " (0x"
<< absl::StrCat(absl::Hex(ret.int_val))
<< "), Success: " << (ret.success ? "Yes" : "No");
}
CHECK(comms->SendTLV(comms::kMsgReturn, sizeof(ret),
reinterpret_cast<uint8_t*>(&ret)));
}
} // namespace client
} // namespace sapi
extern "C" ABSL_ATTRIBUTE_WEAK int main(int argc, char** argv) {
gflags::SetCommandLineOptionWithMode("userspace_coredumper", "false",
gflags::SET_FLAG_IF_DEFAULT);
gflags::ParseCommandLineFlags(&argc, &argv, true);
google::InitGoogleLogging(argv[0]);
// Note regarding the FD usage here: Parent and child seem to make use of the
// same FD, although this is not true. During process setup `dup2()` will be
// called to replace the FD `kSandbox2ClientCommsFD`.
// We do not use a new comms object here as the destructor would close our FD.
sandbox2::Comms comms{sandbox2::Comms::kSandbox2ClientCommsFD};
sandbox2::ForkingClient s2client{&comms};
// Forkserver loop.
while (true) {
pid_t pid = s2client.WaitAndFork();
if (pid == -1) {
LOG(FATAL) << "Could not spawn a new sandboxee";
}
if (pid == 0) {
break;
}
}
// Child thread.
s2client.SandboxMeHere();
// Enable log forwarding if enabled by the sandboxer.
if (s2client.HasMappedFD(sandbox2::LogSink::kLogFDName)) {
s2client.SendLogsToSupervisor();
}
// Run SAPI stub.
while (true) {
sapi::client::ServeRequest(&comms);
}
LOG(FATAL) << "Unreachable";
}