From 29035b55b25461a882b3f4d36d59ba5b3f3a201a Mon Sep 17 00:00:00 2001
From: AnotherTest <ali.mpfard@gmail.com>
Date: Tue, 11 Aug 2020 15:53:02 +0430
Subject: [PATCH] Kernel: Allow moving a process to a new pgrp via setpgid()

---
 Kernel/Syscalls/setpgid.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Kernel/Syscalls/setpgid.cpp b/Kernel/Syscalls/setpgid.cpp
index 457f44e7ed..3e8a09cd43 100644
--- a/Kernel/Syscalls/setpgid.cpp
+++ b/Kernel/Syscalls/setpgid.cpp
@@ -124,10 +124,15 @@ int Process::sys$setpgid(pid_t specified_pid, pid_t specified_pgid)
     ProcessGroupID new_pgid = specified_pgid ? ProcessGroupID(specified_pgid) : process->m_pid.value();
     SessionID current_sid = sid();
     SessionID new_sid = get_sid_from_pgid(new_pgid);
-    if (current_sid != new_sid) {
+    if (new_sid != -1 && current_sid != new_sid) {
         // Can't move a process between sessions.
         return -EPERM;
     }
+    if (new_sid == -1 && new_pgid != process->m_pid.value()) {
+        // The value of the pgid argument is valid, but is not
+        // the calling pid, and is not an existing process group.
+        return -EPERM;
+    }
     // FIXME: There are more EPERM conditions to check for here..
     process->m_pgid = new_pgid;
     return 0;