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Fix out-of-bounds access in setFunctionCode() #412

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Merged
Miq1 merged 1 commit into from
Jun 5, 2025
Merged

Fix out-of-bounds access in setFunctionCode() #412

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10 changes: 4 additions & 6 deletions src/ModbusMessage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -147,13 +147,11 @@ void ModbusMessage::setServerID(uint8_t serverID) {
}

void ModbusMessage::setFunctionCode(uint8_t FC) {
// We accept here that [0], [1] may allocate bytes!
if (MM_data.empty()) {
MM_data.reserve(3); // At least an error message should fit
if (MM_data.size() < 2) {
MM_data.resize(2); // Resize to at least 2 to ensure indices 0 and 1 are valid
MM_data[0] = 0; // Optional: Invalid server ID as a placeholder
}
// No serverID set yet? use a 0 to initialize it to an error-generating value
if (MM_data.size() < 2) MM_data[0] = 0; // intentional invalid server ID!
MM_data[1] = FC;
MM_data[1] = FC; // Safely set the function code
}

// add() variant to copy a buffer into MM_data. Returns updated size
Expand Down