From 1e630fb78a67cceaff3a0c4a1e104c0662316b3e Mon Sep 17 00:00:00 2001
From: Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
Date: Wed, 10 Feb 2021 21:17:30 +0100
Subject: [PATCH] Kernel: Avoid creating unkillable processes

Found by fuzz-syscalls. Can be reproduced by running this in the Shell:

    $ syscall exit_thread

This leaves the process in the 'Dying' state but never actually removes it.

Therefore, avoid this scenario by pretending to exit the entire process.
---
 Kernel/Syscalls/thread.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Kernel/Syscalls/thread.cpp b/Kernel/Syscalls/thread.cpp
index b5896c2796..fc24d2d731 100644
--- a/Kernel/Syscalls/thread.cpp
+++ b/Kernel/Syscalls/thread.cpp
@@ -95,6 +95,12 @@ void Process::sys$exit_thread(Userspace<void*> exit_value)
 {
     REQUIRE_PROMISE(thread);
     cli();
+
+    if (this->thread_count() == 1) {
+        // If this is the last thread, instead kill the process.
+        this->sys$exit(0);
+    }
+
     Thread::current()->exit(reinterpret_cast<void*>(exit_value.ptr()));
     ASSERT_NOT_REACHED();
 }