From a89648e15988471f3854c99f41ab0e47f131032a Mon Sep 17 00:00:00 2001
From: Tom <tomut@yahoo.com>
Date: Sun, 22 Nov 2020 15:25:48 -0700
Subject: [PATCH] Kernel: Inherit shared buffers when forking

We need to create a reference for the new PID for each shared buffer
that the process had a reference to. If the process subsequently
get replaced through exec, those references will be dropped again.
But if exec for some reason fails then other code, such as global
destructors could still expect having access to them.

Fixes #4076
---
 Kernel/SharedBuffer.cpp  | 16 ++++++++++++++++
 Kernel/SharedBuffer.h    |  1 +
 Kernel/Syscalls/fork.cpp |  3 +++
 3 files changed, 20 insertions(+)

diff --git a/Kernel/SharedBuffer.cpp b/Kernel/SharedBuffer.cpp
index 29223bcda7..39cd8681aa 100644
--- a/Kernel/SharedBuffer.cpp
+++ b/Kernel/SharedBuffer.cpp
@@ -121,6 +121,22 @@ void SharedBuffer::share_with(ProcessID peer_pid)
     sanity_check("share_with (new ref)");
 }
 
+void SharedBuffer::share_all_shared_buffers(Process& from_process, Process& with_process)
+{
+    LOCKER(shared_buffers().lock());
+    for (auto& shbuf : shared_buffers().resource()) {
+        auto& shared_buffer = *shbuf.value;
+        if (shared_buffer.m_global)
+            continue;
+        for (auto& ref : shared_buffer.m_refs) {
+            if (ref.pid == from_process.pid()) {
+                shared_buffer.share_with(with_process.pid());
+                break;
+            }
+        }
+    }
+}
+
 void SharedBuffer::deref_for_process(Process& process)
 {
     LOCKER(shared_buffers().lock());
diff --git a/Kernel/SharedBuffer.h b/Kernel/SharedBuffer.h
index f54a7ca7fe..14d714ed40 100644
--- a/Kernel/SharedBuffer.h
+++ b/Kernel/SharedBuffer.h
@@ -70,6 +70,7 @@ public:
     void share_globally() { m_global = true; }
     void deref_for_process(Process& process);
     void disown(ProcessID pid);
+    static void share_all_shared_buffers(Process& from_process, Process& with_process);
     size_t size() const { return m_vmobject->size(); }
     void destroy_if_unused();
     void seal();
diff --git a/Kernel/Syscalls/fork.cpp b/Kernel/Syscalls/fork.cpp
index 86ccdddab5..7d32a2e3c7 100644
--- a/Kernel/Syscalls/fork.cpp
+++ b/Kernel/Syscalls/fork.cpp
@@ -27,6 +27,7 @@
 #include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/Process.h>
+#include <Kernel/SharedBuffer.h>
 #include <Kernel/VM/Region.h>
 
 //#define FORK_DEBUG
@@ -79,6 +80,8 @@ pid_t Process::sys$fork(RegisterState& regs)
     dbg() << "fork: child will begin executing at " << String::format("%w", child_tss.cs) << ":" << String::format("%x", child_tss.eip) << " with stack " << String::format("%w", child_tss.ss) << ":" << String::format("%x", child_tss.esp) << ", kstack " << String::format("%w", child_tss.ss0) << ":" << String::format("%x", child_tss.esp0);
 #endif
 
+    SharedBuffer::share_all_shared_buffers(*this, *child);
+
     {
         ScopedSpinLock lock(m_lock);
         for (auto& region : m_regions) {