Kernel/ProcFS: Allow a process directory to have a null Process pointer

In case we are about to delete the PID directory, we clear the Process
pointer. If someone still holds a reference to the PID directory (by
opening it), we still need to delete the process, but we can't delete
the directory, so we will keep it alive, but any operation on it will
fail by propogating the error to userspace about that the Process was
deleted and therefore there's no meaning to trying to do operations on
the directory.

Fixes #8576.

1 files changed, 58 insertions, 15 deletions

diff --git a/Kernel/ProcessSpecificExposed.cpp b/Kernel/ProcessSpecificExposed.cpp
index 81e1e14be9..ad26f1940b 100644
--- a/Kernel/ProcessSpecificExposed.cpp
+++ b/Kernel/ProcessSpecificExposed.cpp
@@ -93,7 +93,10 @@ KResultOr<size_t> ProcFSProcessStacks::entries_count() const
     auto parent_folder = m_process_folder.strong_ref();
     if (parent_folder.is_null())
         return KResult(EINVAL);
-    return parent_folder->m_associated_process->thread_count();
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return KResult(ESRCH);
+    return process->thread_count();
 }
 
 KResult ProcFSProcessStacks::traverse_as_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
@@ -105,7 +108,9 @@ KResult ProcFSProcessStacks::traverse_as_directory(unsigned fsid, Function<bool(
     callback({ ".", { fsid, component_index() }, 0 });
     callback({ "..", { fsid, parent_folder->component_index() }, 0 });
 
-    auto process = parent_folder->m_associated_process;
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return KResult(ESRCH);
     process->for_each_thread([&](const Thread& thread) {
         int tid = thread.tid().value();
         InodeIdentifier identifier = { fsid, thread.global_procfs_inode_index() };
@@ -120,7 +125,9 @@ RefPtr<ProcFSExposedComponent> ProcFSProcessStacks::lookup(StringView name)
     auto parent_folder = m_process_folder.strong_ref();
     if (parent_folder.is_null())
         return nullptr;
-    auto process = parent_folder->m_associated_process;
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return nullptr;
     RefPtr<ProcFSThreadStack> procfd_stack;
     // FIXME: Try to exit the loop earlier
     process->for_each_thread([&](const Thread& thread) {
@@ -195,7 +202,10 @@ KResultOr<size_t> ProcFSProcessFileDescriptions::entries_count() const
     auto parent_folder = m_process_folder.strong_ref();
     if (parent_folder.is_null())
         return KResult(EINVAL);
-    return parent_folder->m_associated_process->fds().open_count();
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return KResult(ESRCH);
+    return process->fds().open_count();
 }
 KResult ProcFSProcessFileDescriptions::traverse_as_directory(unsigned fsid, Function<bool(FileSystem::DirectoryEntryView const&)> callback) const
 {
@@ -206,7 +216,9 @@ KResult ProcFSProcessFileDescriptions::traverse_as_directory(unsigned fsid, Func
     callback({ ".", { fsid, component_index() }, 0 });
     callback({ "..", { fsid, parent_folder->component_index() }, 0 });
 
-    auto process = parent_folder->m_associated_process;
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return KResult(ESRCH);
     size_t count = 0;
     process->fds().enumerate([&](auto& file_description_metadata) {
         if (!file_description_metadata.is_valid()) {
@@ -225,7 +237,9 @@ RefPtr<ProcFSExposedComponent> ProcFSProcessFileDescriptions::lookup(StringView
     auto parent_folder = m_process_folder.strong_ref();
     if (parent_folder.is_null())
         return nullptr;
-    auto process = parent_folder->m_associated_process;
+    auto process = parent_folder->associated_process();
+    if (process.is_null())
+        return nullptr;
     RefPtr<ProcFSProcessFileDescription> procfd_fd;
     // FIXME: Try to exit the loop earlier
     size_t count = 0;
@@ -259,7 +273,9 @@ private:
         auto parent_folder = m_parent_folder.strong_ref();
         if (parent_folder.is_null())
             return false;
-        auto process = parent_folder->m_associated_process;
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
         JsonObjectSerializer obj { builder };
 #define __ENUMERATE_PLEDGE_PROMISE(x)       \
     if (process->has_promised(Pledge::x)) { \
@@ -295,8 +311,11 @@ private:
         auto parent_folder = m_parent_folder.strong_ref();
         if (parent_folder.is_null())
             return false;
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
         JsonArraySerializer array { builder };
-        for (auto& unveiled_path : parent_folder->m_associated_process->unveiled_paths()) {
+        for (auto& unveiled_path : process->unveiled_paths()) {
             if (!unveiled_path.was_explicitly_unveiled())
                 continue;
             auto obj = array.add_object();
@@ -337,7 +356,9 @@ private:
         auto parent_folder = m_parent_folder.strong_ref();
         if (parent_folder.is_null())
             return false;
-        auto process = parent_folder->m_associated_process;
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
         if (!process->perf_events()) {
             dbgln("ProcFS: No perf events for {}", process->pid());
             return false;
@@ -364,7 +385,9 @@ private:
         if (parent_folder.is_null())
             return false;
         JsonArraySerializer array { builder };
-        auto process = parent_folder->m_associated_process;
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
         if (process->fds().open_count() == 0) {
             array.finish();
             return true;
@@ -414,7 +437,10 @@ private:
         auto parent_folder = m_parent_process_directory.strong_ref();
         if (parent_folder.is_null())
             return false;
-        builder.append_bytes(parent_folder->m_associated_process->root_directory_relative_to_global_root().absolute_path().to_byte_buffer());
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
+        builder.append_bytes(process->root_directory_relative_to_global_root().absolute_path().to_byte_buffer());
         return true;
     }
     WeakPtr<ProcFSProcessDirectory> m_parent_process_directory;
@@ -437,7 +463,9 @@ private:
         auto parent_folder = m_parent_folder.strong_ref();
         if (parent_folder.is_null())
             return false;
-        auto process = parent_folder->m_associated_process;
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
         JsonArraySerializer array { builder };
         {
             ScopedSpinLock lock(process->space().get_lock());
@@ -500,7 +528,10 @@ private:
         auto parent_folder = m_parent_process_directory.strong_ref();
         if (parent_folder.is_null())
             return false;
-        builder.append_bytes(parent_folder->m_associated_process->current_directory().absolute_path().bytes());
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
+        builder.append_bytes(process->current_directory().absolute_path().bytes());
         return true;
     }
 
@@ -519,7 +550,10 @@ public:
         auto parent_folder = m_parent_process_directory.strong_ref();
         if (parent_folder.is_null())
             return false;
-        if (!parent_folder->m_associated_process->executable())
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
+        if (!process->executable())
             return 0;
         return ProcFSExposedComponent::required_mode();
     }
@@ -535,7 +569,10 @@ private:
         auto parent_folder = m_parent_process_directory.strong_ref();
         if (parent_folder.is_null())
             return false;
-        auto* custody = parent_folder->m_associated_process->executable();
+        auto process = parent_folder->associated_process();
+        if (process.is_null())
+            return false;
+        auto* custody = process->executable();
         if (!custody)
             return false;
         builder.append(custody->absolute_path().bytes());
@@ -582,6 +619,12 @@ NonnullRefPtr<ProcFSProcessDirectory> ProcFSProcessDirectory::create(const Proce
     return adopt_ref_if_nonnull(new (nothrow) ProcFSProcessDirectory(process)).release_nonnull();
 }
 
+void ProcFSProcessDirectory::prepare_for_deletion()
+{
+    ProcFSExposedDirectory::prepare_for_deletion();
+    m_associated_process.clear();
+}
+
 ProcFSProcessDirectory::ProcFSProcessDirectory(const Process& process)
     : ProcFSExposedDirectory(String::formatted("{:d}", process.pid().value()), ProcFSComponentRegistry::the().root_folder())
     , m_associated_process(process)