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Kernel: Make ProcessGroup a ListedRefCounted and fix two races

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This closes two race windows:

- ProcessGroup removed itself from the "all process groups" list in its
  destructor. It was possible to walk the list between the last unref()
  and the destructor invocation, and grab a pointer to a ProcessGroup
  that was about to get deleted.

- sys$setsid() could end up creating a process group that already
  existed, as there was a race window between checking if the PGID
  is used, and actually creating a ProcessGroup with that PGID.
This commit is contained in:
Andreas Kling 2023-04-04 16:38:46 +02:00
parent 37bfc36601
commit 3e30d9bc99
3 changed files with 29 additions and 36 deletions
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37
Kernel/ProcessGroup.cpp
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@ -1,6 +1,6 @@
/*
* Copyright (c) 2020, the SerenityOS developers.
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021-2023, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -10,45 +10,44 @@
namespace Kernel {
static Singleton<SpinlockProtected<ProcessGroup::List, LockRank::None>> s_process_groups;
static Singleton<SpinlockProtected<ProcessGroup::AllInstancesList, LockRank::None>> s_all_instances;
SpinlockProtected<ProcessGroup::List, LockRank::None>& process_groups()
SpinlockProtected<ProcessGroup::AllInstancesList, LockRank::None>& ProcessGroup::all_instances()
{
return *s_process_groups;
return s_all_instances;
}
ProcessGroup::~ProcessGroup()
{
process_groups().with([&](auto& groups) {
groups.remove(*this);
});
}
ProcessGroup::~ProcessGroup() = default;
ErrorOr<NonnullRefPtr<ProcessGroup>> ProcessGroup::create(ProcessGroupID pgid)
ErrorOr<NonnullRefPtr<ProcessGroup>> ProcessGroup::create_if_unused_pgid(ProcessGroupID pgid)
{
auto process_group = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) ProcessGroup(pgid)));
process_groups().with([&](auto& groups) {
groups.prepend(*process_group);
return all_instances().with([&](auto& all_instances) -> ErrorOr<NonnullRefPtr<ProcessGroup>> {
for (auto& process_group : all_instances) {
if (process_group.pgid() == pgid)
return EPERM;
}
auto process_group = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) ProcessGroup(pgid)));
all_instances.prepend(*process_group);
return process_group;
});
return process_group;
}
ErrorOr<NonnullRefPtr<ProcessGroup>> ProcessGroup::find_or_create(ProcessGroupID pgid)
{
return process_groups().with([&](auto& groups) -> ErrorOr<NonnullRefPtr<ProcessGroup>> {
for (auto& group : groups) {
return all_instances().with([&](auto& all_instances) -> ErrorOr<NonnullRefPtr<ProcessGroup>> {
for (auto& group : all_instances) {
if (group.pgid() == pgid)
return group;
}
auto process_group = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) ProcessGroup(pgid)));
groups.prepend(*process_group);
all_instances.prepend(*process_group);
return process_group;
});
}
RefPtr<ProcessGroup> ProcessGroup::from_pgid(ProcessGroupID pgid)
{
return process_groups().with([&](auto& groups) -> RefPtr<ProcessGroup> {
return all_instances().with([&](auto& groups) -> RefPtr<ProcessGroup> {
for (auto& group : groups) {
if (group.pgid() == pgid)
return &group;