[XCM] Panic in the specific case of reserveTransferAssets when it contains multiple assets

[jiguantong]

Polkadot related version: v0.9.26
XCM version: 2
Possible related issue: paritytech/cumulus#1700

This seems to be related to the order of MultiAssets as @KiChjang mentioned here, because it won't panic if I reorder the assets.

This would not only happen on parachains, but also on relay chains

TestCase

1. MultiAssets: 0: {parents: 0, interior: X1(PalletInstance(7)} 1: {parents: 0, interior: X1(PalletInstance(5)}

Encoded call data on pangolin parachain: 0x0d0201010100a10f0100010100d43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d01080000010407001ec806000000010405001ed1430001000000

The console log of chrome:

2022-09-29 08:21:47        RPC-CORE: submitAndWatchExtrinsic(extrinsic: Extrinsic): ExtrinsicStatus:: 1002: Verification Error: Runtime error: Execution failed: Execution aborted due to trap: wasm trap: wasm `unreachable` instruction executed
WASM backtrace:

    0: 0x260bfa - <unknown>!rust_begin_unwind
    1: 0x67dc - <unknown>!core::panicking::panic_fmt::h781687f2782526ba
    2: 0xd1eb0 - <unknown>!TaggedTransactionQueue_validate_transaction
: Runtime error: Execution failed: Execution aborted due to trap: wasm trap: wasm `unreachable` instruction executed
WASM backtrace:

    0: 0x260bfa - <unknown>!rust_begin_unwind
    1: 0x67dc - <unknown>!core::panicking::panic_fmt::h781687f2782526ba

And if I test it on my dev node, the node log shows: pangolin-parachain/src/lib.rs:194:1

2022-09-29 08:12:33.560 ERROR tokio-runtime-worker runtime: panicked at 'Bad input data provided to query_info: Codec error', /home/workspace/test/darwinia-parachain/runtime/pangolin-parachain/src/lib.rs:194:1
2022-09-29 08:12:34.379 ERROR tokio-runtime-worker runtime: panicked at 'Bad input data provided to validate_transaction: Codec error', /home/workspace/test/darwinia-parachain/runtime/pangolin-parachain/src/lib.rs:194:1

2. It won't panic if I swap the order of assets, MultiAssets: 0: {parents: 0, interior: X1(PalletInstance(5)} 1: {parents: 0, interior: X1(PalletInstance(7)}

Encoded call data on pangolin parachain:
0x0d0201010100a10f0100010100d43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d01080000010405001ec806000000010407001ed1430001000000

[xlc]

This is expected behavior. You are passing an invalid data. As you already discovered, the order of assets must sorted or it will panic.

[jiguantong]

This is expected behavior. You are passing an invalid data. As you already discovered, the order of assets must sorted or it will panic.

Really? I don't think it's UX friendly

[KiChjang]

I've posted this issue on polkadot.js before: polkadot-js/api#4537.

On the chain side, we have to get the MultiAssets sorted, because we specifically want them to not contain duplicate entries, otherwise the validation algorithm would be an O(NlogN) operation instead of it being O(N).

In other words, this is really a UI/UX issue, and we won't fix it on the chain side.

[jiguantong]

Ok, I see.