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fix: keep is_ready error_string_shm alive until parent ack #459

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dundysm wants to merge 1 commit into from
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fix: keep is_ready error_string_shm alive until parent ack #459

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8 changes: 6 additions & 2 deletions src/pb_stub.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1632,6 +1632,10 @@ Stub::ProcessUserModelReadinessRequest(std::unique_ptr<IPCMessage>& ipc_message)
bool function_exists = false;
bool has_exception = false;
std::string error_string;
// Keep error_string_shm alive until after parent ack so the parent can
// LoadFromSharedMemory the handle before this function returns and frees it.
// Same lifetime pattern as GetCUDAMemoryPoolAddress above.
std::unique_ptr<PbString> error_string_shm;

@greptile-apps greptile-apps Bot Oct 2, 2026

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P1 Error string can expire early If the parent sees the readiness response but is delayed for more than five seconds before loading its error string, the stub’s acknowledgement wait times out and destroys error_string_shm. The parent can then load a freed shared-memory handle, leaving the use-after-free possible despite this change.

Knowledge Base Used: Python stub process and IPC


try {
py::gil_scoped_acquire acquire;
Expand Down Expand Up @@ -1673,7 +1677,6 @@ Stub::ProcessUserModelReadinessRequest(std::unique_ptr<IPCMessage>& ipc_message)
readiness_payload->error = 0;

if (has_exception) {
std::unique_ptr<PbString> error_string_shm;
LOG_IF_EXCEPTION(
error_string_shm = PbString::Create(shm_pool_, error_string));
if (error_string_shm != nullptr) {
Expand All @@ -1689,7 +1692,8 @@ Stub::ProcessUserModelReadinessRequest(std::unique_ptr<IPCMessage>& ipc_message)
readiness_payload->waiting_on_stub = true;
ipc_message->ResponseCondition()->notify_all();

// Wait for parent ack with timeout to avoid deadlock
// Wait for parent ack with timeout to avoid deadlock. Required so
// error_string_shm stays alive until the parent finishes reading it.
boost::posix_time::ptime timeout =
boost::get_system_time() +
boost::posix_time::milliseconds(kUserModelReadinessTimeoutMs);
Expand Down