More efficient fork request handling and #Cleanup

- Assign to `*mutable_XXX()` instead of looping
- Use a const ref for capabilities

PiperOrigin-RevId: 384192675
Change-Id: I4db3d0c8ce0d7f6acc9fd486a2409962516b5fe7

sandboxed_api/sandbox2/executor.cc

@@ -50,7 +50,7 @@ std::vector<std::string> Executor::CopyEnviron() {
 }
 
 pid_t Executor::StartSubProcess(int32_t clone_flags, const Namespace* ns,
-                                const std::vector<int>* caps,
+                                const std::vector<int>& caps,
                                 pid_t* init_pid_out) {
   if (started_) {
     LOG(ERROR) << "This executor has already been started";
@@ -76,12 +76,8 @@ pid_t Executor::StartSubProcess(int32_t clone_flags, const Namespace* ns,
   }
 
   ForkRequest request;
-  for (size_t i = 0; i < argv_.size(); i++) {
-    request.add_args(argv_[i]);
-  }
-  for (size_t i = 0; i < envp_.size(); i++) {
-    request.add_envs(envp_[i]);
-  }
+  *request.mutable_args() = {argv_.begin(), argv_.end()};
+  *request.mutable_envs() = {envp_.begin(), envp_.end()};
 
   // Add LD_ORIGIN_PATH to envs, as it'll make the amount of syscalls invoked by
   // ld.so smaller.
@@ -113,15 +109,13 @@ pid_t Executor::StartSubProcess(int32_t clone_flags, const Namespace* ns,
 
   request.set_clone_flags(clone_flags);
 
-  if (caps) {
-    for (auto cap : *caps) {
+  for (auto cap : caps) {
     request.add_capabilities(cap);
   }
-  }
 
   int ns_fd = -1;
   if (libunwind_sbox_for_pid_ != 0) {
-    std::string ns_path =
+    const std::string ns_path =
         absl::StrCat("/proc/", libunwind_sbox_for_pid_, "/ns/user");
     PCHECK((ns_fd = open(ns_path.c_str(), O_RDONLY)) != -1)
         << "Could not open user ns fd (" << ns_path << ")";

sandboxed_api/sandbox2/executor.h

@@ -125,7 +125,7 @@ class Executor final {
   //
   // Returns the same values as fork().
   pid_t StartSubProcess(int clone_flags, const Namespace* ns = nullptr,
-                        const std::vector<int>* caps = nullptr,
+                        const std::vector<int>& caps = {},
                         pid_t* init_pid_out = nullptr);
 
   // Whether the Executor has been started yet

sandboxed_api/sandbox2/monitor.cc

@@ -266,7 +266,7 @@ void Monitor::Run() {
   // Get PID of the sandboxee.
   pid_t init_pid = 0;
   bool should_have_init = ns && (ns->GetCloneFlags() & CLONE_NEWPID);
-  pid_ = executor_->StartSubProcess(clone_flags, ns, policy_->GetCapabilities(),
+  pid_ = executor_->StartSubProcess(clone_flags, ns, policy_->capabilities(),
                                     &init_pid);
 
   if (init_pid > 0) {

sandboxed_api/sandbox2/policy.cc

@@ -169,7 +169,11 @@ void Policy::AllowUnsafeKeepCapabilities(
   if (namespace_) {
     namespace_->DisableUserNamespace();
   }
-  capabilities_ = std::move(caps);
+  if (!caps) {
+    capabilities_.clear();
+  } else {
+    capabilities_ = {caps->begin(), caps->end()};
+  }
 }
 
 void Policy::GetPolicyDescription(PolicyDescription* policy) const {
@@ -185,11 +189,9 @@ void Policy::GetPolicyDescription(PolicyDescription* policy) const {
         policy->mutable_namespace_description());
   }
 
-  if (capabilities_) {
-    for (const auto& cap : *capabilities_) {
+  for (const auto& cap : capabilities_) {
     policy->add_capabilities(cap);
   }
-  }
 }
 
 }  // namespace sandbox2

sandboxed_api/sandbox2/policy.h

@@ -42,7 +42,7 @@ namespace sandbox2 {
 namespace internal {
 // Magic values of registers when executing sys_execveat, so we can recognize
 // the pre-sandboxing state and notify the Monitor
-constexpr uintptr_t kExecveMagic = 0x921c2c34;
+inline constexpr uintptr_t kExecveMagic = 0x921c2c34;
 }  // namespace internal
 
 class Comms;
@@ -79,9 +79,7 @@ class Policy final {
     namespace_ = std::move(ns);
   }
 
-  const std::vector<int>* GetCapabilities() const {
-    return capabilities_.get();
-  }
+  const std::vector<int>& capabilities() const { return capabilities_; }
 
   // Returns the default policy, which blocks certain dangerous syscalls and
   // mismatched syscall tables.
@@ -100,7 +98,7 @@ class Policy final {
   bool collect_stacktrace_on_kill_ = true;
 
   // The capabilities to keep in the sandboxee.
-  std::unique_ptr<std::vector<int>> capabilities_;
+  std::vector<int> capabilities_;
 
   // Optional pointer to a PolicyBuilder description pb object.
   std::unique_ptr<PolicyBuilderDescription> policy_builder_description_;