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Kernel: Make ProcessGroup a ListedRefCounted and fix two races
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$setsid() could end up creating a process group that already existed, as there was a race window between checking if the PGID is used, and actually creating a ProcessGroup with that PGID.
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3 changed files with 29 additions and 36 deletions
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@ -28,16 +28,10 @@ ErrorOr<FlatPtr> Process::sys$setsid()
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{
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VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
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TRY(require_promise(Pledge::proc));
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bool found_process_with_same_pgid_as_my_pid = false;
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TRY(Process::for_each_in_pgrp_in_same_jail(pid().value(), [&](auto&) -> ErrorOr<void> {
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found_process_with_same_pgid_as_my_pid = true;
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return {};
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}));
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if (found_process_with_same_pgid_as_my_pid)
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return EPERM;
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// Create a new Session and a new ProcessGroup.
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auto process_group = TRY(ProcessGroup::create(ProcessGroupID(pid().value())));
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// NOTE: ProcessGroup::create_if_unused_pgid() will fail with EPERM
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// if a process group with the same PGID already exists.
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auto process_group = TRY(ProcessGroup::create_if_unused_pgid(ProcessGroupID(pid().value())));
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return with_mutable_protected_data([&](auto& protected_data) -> ErrorOr<FlatPtr> {
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protected_data.tty = nullptr;
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protected_data.process_group = move(process_group);
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