Uncaught Panic in ORML Rewards Pallet

Summary

## Summary A vulnerability in the `add_share` function of the **Rewards** pallet (part of the ORML repository) can lead to an uncaught Rust panic when handling user-provided input exceeding the `u128` range.

## Affected Components - **ORML Rewards** pallet (`rewards/src/lib.rs`) - Any Substrate-based chain using ORML Rewards with `add_share` accepting unvalidated large `u128` inputs

## Technical Details - `add_share` performs arithmetic on user-supplied values (`add_amount`) of type `T::Share` (mapped to `u128` in Acala). - If `add_amount` is large enough (e.g., `i128::MAX`), the intermediate result may overflow and panic on the cast to `u128`. - Validation occurs only after arithmetic, enabling a crafted input to trigger an overflow.

## Impact A malicious user submitting a specially crafted extrinsic can cause a panic in the runtime: - **Denial of Service** by crashing the node process. - **Potential for invalid blocks** produced by validators.

## Likelihood This issue is exploitable in production if there exists at least one rewards pool where reward tokens exceed twice the collateral tokens, allowing sufficiently large multiplication to exceed `u128` bounds.

## Remediation - This issue is fixed in https://github.com/open-web3-stack/open-runtime-module-library/pull/1016

## Backport

The patch have been backported to following release branches: - polkadot-stable2407 - polkadot-stable2409

A 1.0.1 patch release is made with this fix.