Kernel: Guard Process "protected data" with a spinlock

This ensures that both mutable and immutable access to the protected
data of a process is serialized.

Note that there may still be multiple TOCTOU issues around this, as we
have a bunch of convenience accessors that make it easy to introduce
them. We'll need to audit those as well.

1 files changed, 4 insertions, 3 deletions

diff --git a/Kernel/Syscalls/setpgid.cpp b/Kernel/Syscalls/setpgid.cpp
index 92dbc681ba..b6473484e7 100644
--- a/Kernel/Syscalls/setpgid.cpp
+++ b/Kernel/Syscalls/setpgid.cpp
@@ -40,9 +40,10 @@ ErrorOr<FlatPtr> Process::sys$setsid()
 
     m_pg = TRY(ProcessGroup::try_create(ProcessGroupID(pid().value())));
     m_tty = nullptr;
-    ProtectedDataMutationScope scope { *this };
-    m_protected_values.sid = pid().value();
-    return sid().value();
+    return with_mutable_protected_data([&](auto& protected_data) -> ErrorOr<FlatPtr> {
+        protected_data.sid = pid().value();
+        return protected_data.sid.value();
+    });
 }
 
 ErrorOr<FlatPtr> Process::sys$getpgid(pid_t pid)