sandboxed_api: Expose strlen in the rpc channel

PiperOrigin-RevId: 281958333
Change-Id: If15d7d5b915fec3c5521ef53ee44c58d7482d1bc

sandboxed_api/call.h

@@ -38,6 +38,7 @@ constexpr uint32_t kMsgSendFd = 0x106;
 constexpr uint32_t kMsgRecvFd = 0x107;
 constexpr uint32_t kMsgClose = 0x108;
 constexpr uint32_t kMsgReallocate = 0x109;
+constexpr uint32_t kMsgStrlen = 0x10A;
 // Return:
 constexpr uint32_t kMsgReturn = 0x201;
 

sandboxed_api/client.cc

@@ -329,6 +329,12 @@ void HandleCloseFd(sandbox2::Comms* comms, int fd_to_close, FuncRet* ret) {
   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>(),
@@ -394,6 +400,11 @@ void ServeRequest(sandbox2::Comms* comms) {
       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

sandboxed_api/examples/stringop/lib/BUILD.bazel

@@ -12,12 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-licenses(["notice"])
-
 load("//sandboxed_api/bazel:build_defs.bzl", "sapi_platform_copts")
 load("//sandboxed_api/bazel:proto.bzl", "sapi_proto_library")
 load("//sandboxed_api/bazel:sapi.bzl", "sapi_library")
 
+licenses(["notice"])
+
 sapi_proto_library(
     name = "stringop_params_proto",
     srcs = ["stringop_params.proto"],
@@ -47,6 +47,7 @@ sapi_library(
         "pb_reverse_string",
         "nop",
         "violate",
+        "get_raw_c_string",
     ],
     input_files = [
         "stringop.cc",

sandboxed_api/examples/stringop/lib/CMakeLists.txt

@@ -51,6 +51,7 @@ add_sapi_library(stringop-sapi
             pb_reverse_string
             nop
             violate
+            get_raw_c_string
   INPUTS stringop.cc
   LIBRARY sapi_stringop
   LIBRARY_NAME Stringop

sandboxed_api/examples/stringop/lib/stringop.cc

@@ -48,7 +48,6 @@ extern "C" int reverse_string(sapi::LenValStruct* input) {
   for (size_t i = 0; i < input->size; i++) {
     new_buf[i] = src_buf[input->size - i - 1];
   }
-
   // Free old value.
   free(input->data);
   // Replace pointer to our new string.
@@ -74,6 +73,8 @@ extern "C" int duplicate_string(sapi::LenValStruct* input) {
   return 1;
 }
 
+extern "C" const void* get_raw_c_string() { return "Ten chars."; }
+
 extern "C" void nop() {}
 
 extern "C" void violate() { ptrace((__ptrace_request)990, 991, 992, 993); }

sandboxed_api/examples/stringop/main_stringop.cc

@@ -130,4 +130,14 @@ TEST(StringopTest, RawStringReversal) {
   }
 }
 
+TEST(StringopTest, RawStringLength) {
+  StringopSapiSandbox sandbox;
+  ASSERT_THAT(sandbox.Init(), IsOk());
+  StringopApi api(&sandbox);
+  SAPI_ASSERT_OK_AND_ASSIGN(void* target_mem_ptr, api.get_raw_c_string());
+  SAPI_ASSERT_OK_AND_ASSIGN(uint64_t len,
+                       sandbox.GetRpcChannel()->Strlen(target_mem_ptr));
+  EXPECT_THAT(len, Eq(10));
+}
+
 }  // namespace

sandboxed_api/rpcchannel.cc

@@ -17,6 +17,7 @@
 #include <glog/logging.h>
 #include "absl/strings/str_cat.h"
 #include "absl/synchronization/mutex.h"
+#include "sandboxed_api/call.h"
 #include "sandboxed_api/sandbox2/comms.h"
 #include "sandboxed_api/util/canonical_errors.h"
 #include "sandboxed_api/util/status_macros.h"
@@ -204,4 +205,18 @@ sapi::Status RPCChannel::Close(int remote_fd) {
   return sapi::OkStatus();
 }
 
+sapi::StatusOr<uint64_t> RPCChannel::Strlen(void* str) {
+  absl::MutexLock lock(&mutex_);
+  if (!comms_->SendTLV(comms::kMsgStrlen, sizeof(str),
+                       reinterpret_cast<uint8_t*>(&str))) {
+    return sapi::UnavailableError("Sending TLV value failed");
+  }
+
+  SAPI_ASSIGN_OR_RETURN(auto fret, Return(v::Type::kInt));
+  if (!fret.success) {
+    return sapi::UnavailableError("Close() failed on the remote side");
+  }
+  return fret.int_val;
+}
+
 }  // namespace sapi

sandboxed_api/rpcchannel.h

@@ -60,6 +60,9 @@ class RPCChannel {
   // Closes fd in sandboxee.
   sapi::Status Close(int remote_fd);
 
+  // Returns length of a null-terminated c-style string (invokes strlen).
+  sapi::StatusOr<uint64_t> Strlen(void* str);
+
   sandbox2::Comms* comms() const { return comms_; }
 
  private: