[lldb] Fix a use-after-free in SymbolFileCTF

This fixes a use-after-free in SymbolFileCTF. Previously, we would
remove the underlying CTF type as soon as we resolved it. However, it's
possible that we're still holding onto the CTF type while we're parsing
a dependent type, like a modifier, resulting in a use-after-free. This
patch addresses the issue by delaying the removal of the CTF type until
the type is fully resolved.

I have a XNU kernel binary that reproduces the issue and confirmed that
this solves the memory issue using ASan. However I haven't been able to
craft types by hand that reproduce this issue for a test case.

rdar://156660866

Author: JDevlieghere

lldb/source/Plugins/SymbolFile/CTF/SymbolFileCTF.cpp

@@ -738,9 +738,29 @@ size_t SymbolFileCTF::ParseTypes(CompileUnit &cu) {
 
   LLDB_LOG(log, "Parsed {0} CTF types", m_ctf_types.size());
 
-  for (lldb::user_id_t uid = 1; uid < type_uid; ++uid)
+  for (lldb::user_id_t uid = 1; uid < type_uid; ++uid) {
     ResolveTypeUID(uid);
 
+    // Remove the CTF type because we don't need it anymore, except for record
+    // types which we may need to complete later.
+    auto ctf_type_it = m_ctf_types.find(uid);
+    if (ctf_type_it != m_ctf_types.end()) {
+      CTFType *ctf_type = ctf_type_it->second.get();
+      if (!llvm::isa<CTFRecord>(ctf_type))
+        m_ctf_types.erase(uid);
+    }
+  }
+
+#ifndef NDEBUG
+  // Verify that the only CTF types left at this point are record types.
+  for (auto &t : m_ctf_types) {
+    CTFType *ctf_type = t.second.get();
+    assert(ctf_type && "invalid type in m_ctf_types");
+    assert(llvm::isa<CTFRecord>(ctf_type) && "leaking non record type");
+  }
+
+#endif
+
   LLDB_LOG(log, "Created {0} CTF types", m_types.size());
 
   return m_types.size();
@@ -994,6 +1014,8 @@ lldb_private::Type *SymbolFileCTF::ResolveTypeUID(lldb::user_id_t type_uid) {
 
   CTFType *ctf_type = ctf_type_it->second.get();
   assert(ctf_type && "m_ctf_types should only contain valid CTF types");
+  assert(ctf_type->uid == type_uid &&
+         "CTF type UID doesn't match UID in m_ctf_types");
 
   Log *log = GetLog(LLDBLog::Symbols);
 
@@ -1015,11 +1037,6 @@ lldb_private::Type *SymbolFileCTF::ResolveTypeUID(lldb::user_id_t type_uid) {
 
   m_types[type_uid] = type_sp;
 
-  // Except for record types which we'll need to complete later, we don't need
-  // the CTF type anymore.
-  if (!isa<CTFRecord>(ctf_type))
-    m_ctf_types.erase(type_uid);
-
   return type_sp.get();
 }