From 3cbd871454dd9d22376c91162952e51dedbf9896 Mon Sep 17 00:00:00 2001
From: Kevin Hamacher <hamacher@google.com>
Date: Fri, 22 Nov 2019 06:59:37 -0800
Subject: [PATCH] Allow sandboxee c-strings to be read as std::string

PiperOrigin-RevId: 281960106
Change-Id: I54256dda2b6b0374d0f2ce3f762370478b912683
---
 .../examples/stringop/main_stringop.cc        | 14 +++++++
 sandboxed_api/sandbox.cc                      | 37 +++++++++++++++++++
 sandboxed_api/sandbox.h                       |  4 ++
 3 files changed, 55 insertions(+)

diff --git a/sandboxed_api/examples/stringop/main_stringop.cc b/sandboxed_api/examples/stringop/main_stringop.cc
index 27728e1..bf4348d 100644
--- a/sandboxed_api/examples/stringop/main_stringop.cc
+++ b/sandboxed_api/examples/stringop/main_stringop.cc
@@ -140,4 +140,18 @@ TEST(StringopTest, RawStringLength) {
   EXPECT_THAT(len, Eq(10));
 }
 
+TEST(StringopTest, RawStringReading) {
+  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));
+
+  SAPI_ASSERT_OK_AND_ASSIGN(std::string data,
+                       sandbox.GetCString(sapi::v::RemotePtr(target_mem_ptr)));
+  EXPECT_THAT(data, StrEq("Ten chars."));
+}
+
 }  // namespace
diff --git a/sandboxed_api/sandbox.cc b/sandboxed_api/sandbox.cc
index 2eaab90..6485d7f 100644
--- a/sandboxed_api/sandbox.cc
+++ b/sandboxed_api/sandbox.cc
@@ -391,6 +391,43 @@ sapi::Status Sandbox::TransferFromSandboxee(v::Var* var) {
   return var->TransferFromSandboxee(GetRpcChannel(), GetPid());
 }
 
+sapi::StatusOr<std::string> Sandbox::GetCString(const v::RemotePtr& str,
+                                                  uint64_t max_length) {
+  if (!IsActive()) {
+    return sapi::UnavailableError("Sandbox not active");
+  }
+
+  SAPI_ASSIGN_OR_RETURN(auto len, GetRpcChannel()->Strlen(str.GetValue()));
+  if (len > max_length) {
+    return sapi::InvalidArgumentError(
+        absl::StrCat("Target string too large: ", len, " > ", max_length));
+  }
+  std::string buffer(len, '\0');
+  struct iovec local = {
+      .iov_base = &buffer[0],
+      .iov_len = len,
+  };
+  struct iovec remote = {
+      .iov_base = str.GetValue(),
+      .iov_len = len,
+  };
+
+  ssize_t ret = process_vm_readv(pid_, &local, 1, &remote, 1, 0);
+  if (ret == -1) {
+    PLOG(WARNING) << "reading c-string failed: process_vm_readv(pid: " << pid_
+                  << " raddr: " << str.GetValue() << " size: " << len << ")";
+    return sapi::UnavailableError("process_vm_readv failed");
+  }
+  if (ret != len) {
+    LOG(WARNING) << "partial read when reading c-string: process_vm_readv(pid: "
+                 << pid_ << " raddr: " << str.GetValue() << " size: " << len
+                 << ") transferred " << ret << " bytes";
+    return sapi::UnavailableError("process_vm_readv succeeded partially");
+  }
+
+  return buffer;
+}
+
 const sandbox2::Result& Sandbox::AwaitResult() {
   if (s2_) {
     result_ = s2_->AwaitResult();
diff --git a/sandboxed_api/sandbox.h b/sandboxed_api/sandbox.h
index 70ed2f5..b068e87 100644
--- a/sandboxed_api/sandbox.h
+++ b/sandboxed_api/sandbox.h
@@ -95,6 +95,10 @@ class Sandbox {
   sapi::Status TransferToSandboxee(v::Var* var);
   sapi::Status TransferFromSandboxee(v::Var* var);
 
+  sapi::StatusOr<std::string> GetCString(const v::RemotePtr& str,
+                                           uint64_t max_length = 10 * 1024 *
+                                                                 1024);
+
   // Waits until the sandbox terminated and returns the result.
   const sandbox2::Result& AwaitResult();
   const sandbox2::Result& result() const { return result_; }