support_mixed_sandbox_with_zygote.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jeremy Apthorp <nornagon@nornagon.net>
Date: Wed, 28 Nov 2018 13:20:27 -0800
Subject: support_mixed_sandbox_with_zygote.patch

On Linux, Chromium launches all new renderer processes via a "zygote"
process which has the sandbox pre-initialized (see
//docs/linux_zygote.md). In order to support mixed-sandbox mode, in
which some renderers are launched with the sandbox engaged and others
without it, we need the option to launch non-sandboxed renderers without
going through the zygote.

Chromium already supports a `--no-zygote` flag, but it turns off the
zygote completely, and thus also disables sandboxing. This patch allows
the `--no-zygote` flag to affect renderer processes on a case-by-case
basis, checking immediately prior to launch whether to go through the
zygote or not based on the command-line of the to-be-launched renderer.

This patch could conceivably be upstreamed, as it does not affect
production Chromium (which does not use the `--no-zygote` flag).
However, the patch would need to be reviewed by the security team, as it
does touch a security-sensitive class.

diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index a5e1e13fb11996d4df926480ded2b901de08b75a..9e9316c0bbbecbf425fb04f2cef9bb4f5caf98c6 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -429,10 +429,18 @@ class RendererSandboxedProcessLauncherDelegate
  public:
   RendererSandboxedProcessLauncherDelegate() = default;
 
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+  RendererSandboxedProcessLauncherDelegate(bool use_zygote):
+    use_zygote_(use_zygote) {}
+#endif
+
   ~RendererSandboxedProcessLauncherDelegate() override = default;
 
 #if BUILDFLAG(USE_ZYGOTE_HANDLE)
   ZygoteHandle GetZygote() override {
+    if (!use_zygote_) {
+      return nullptr;
+    }
     const base::CommandLine& browser_command_line =
         *base::CommandLine::ForCurrentProcess();
     base::CommandLine::StringType renderer_prefix =
@@ -450,6 +458,11 @@ class RendererSandboxedProcessLauncherDelegate
   sandbox::policy::SandboxType GetSandboxType() override {
     return sandbox::policy::SandboxType::kRenderer;
   }
+
+ private:
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+  bool use_zygote_ = true;
+#endif
 };
 
 #if defined(OS_WIN)
@@ -461,6 +474,9 @@ class RendererSandboxedProcessLauncherDelegateWin
                                               bool is_jit_disabled)
       : renderer_code_integrity_enabled_(
             GetContentClient()->browser()->IsRendererCodeIntegrityEnabled()) {
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+    use_zygote_ = !cmd_line->HasSwitch(switches::kNoZygote);
+#endif
     if (is_jit_disabled) {
       dynamic_code_can_be_disabled_ = true;
       return;
@@ -2056,9 +2072,15 @@ bool RenderProcessHostImpl::Init() {
     std::unique_ptr<SandboxedProcessLauncherDelegate> sandbox_delegate =
         std::make_unique<RendererSandboxedProcessLauncherDelegateWin>(
             cmd_line.get(), IsJitDisabled());
+#else
+#if BUILDFLAG(USE_ZYGOTE_HANDLE)
+    bool use_zygote = !cmd_line->HasSwitch(switches::kNoZygote);
+    std::unique_ptr<SandboxedProcessLauncherDelegate> sandbox_delegate =
+        std::make_unique<RendererSandboxedProcessLauncherDelegate>(use_zygote);
 #else
     std::unique_ptr<SandboxedProcessLauncherDelegate> sandbox_delegate =
         std::make_unique<RendererSandboxedProcessLauncherDelegate>();
+#endif
 #endif
     // Spawn the child process asynchronously to avoid blocking the UI thread.
     // As long as there's no renderer prefix, we can use the zygote process