From c14312c3a2c3699ba2d574d24d17c5f8eeaa06e3 Mon Sep 17 00:00:00 2001
From: Wiktor Garbacz <wiktorg@google.com>
Date: Wed, 9 Aug 2023 05:59:49 -0700
Subject: [PATCH] Kill on each iteration of graceful exit loop

I believe it's possible for the `main_pid` to disappear between `kill` and `sigtimedwait` by means of an `exec` from a multithreaded process (`PTRACE_EVENT_EXIT` happens after the `exec`ing thread changes its tid to main_pid)

PiperOrigin-RevId: 555137959
Change-Id: Id22908fb31497c0906e4f4fda66400fbf9ac9efb
---
 sandboxed_api/sandbox2/monitor_ptrace.cc | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/sandboxed_api/sandbox2/monitor_ptrace.cc b/sandboxed_api/sandbox2/monitor_ptrace.cc
index 803fa83..5589d46 100644
--- a/sandboxed_api/sandbox2/monitor_ptrace.cc
+++ b/sandboxed_api/sandbox2/monitor_ptrace.cc
@@ -407,10 +407,6 @@ void PtraceMonitor::Run() {
     const bool log_stack_traces =
         result_.final_status() != Result::OK &&
         absl::GetFlag(FLAGS_sandbox2_log_all_stack_traces);
-    if (!log_stack_traces) {
-      // Try to make sure main pid is killed and reaped
-      kill(process_.main_pid, SIGKILL);
-    }
     constexpr auto kGracefullExitTimeout = absl::Milliseconds(200);
     auto deadline = absl::Now() + kGracefullExitTimeout;
     if (log_stack_traces) {
@@ -432,9 +428,12 @@ void PtraceMonitor::Run() {
         }
         break;
       }
-      if (!log_stack_traces && ret == process_.main_pid &&
-          (WIFSIGNALED(status) || WIFEXITED(status))) {
-        break;
+      if (!log_stack_traces) {
+        if (ret == process_.main_pid &&
+            (WIFSIGNALED(status) || WIFEXITED(status))) {
+          break;
+        }
+        kill(process_.main_pid, SIGKILL);
       }
 
       if (ret == 0) {
@@ -454,10 +453,6 @@ void PtraceMonitor::Run() {
           continue;
         }
       }
-
-      if (!log_stack_traces) {
-        kill(process_.main_pid, SIGKILL);
-      }
     }
   }
 }