This causes crash on elements wallet when dealing with transactions that
have explicit values and confidential assets. This creates a somewhat
serious DoS attack as the sender can cause the reciever's wallet to
crash by partially blinding the change output. To make matters worse,
the wallet initially accepts the transaction, but fails while spending
the output.
This is likely caused by a combination of two bugs:
1) The wallet's current behaviour stores the complete transaction of interest
in CWalletTx instead of just Outpoints. Only that the spend time do we
iterate over all outputs, try to unblind them and check which are
isMine. When calling wtx.GetOutputValueOut() or similar calls, we hit this assertion.
While the current behaviour is okay, I think the correct way is move
the IsMine == ISMINE_NO at the start of the loop. We should not do be
any checks on outputs that are not ours. This is used in multiple
places at different parts of the codebase for different RPCs.
2) When dealing with partially blinded trasactions, ComputeBlindingData
correctly sets value = -1, and the cache byte to 1. When getting the
data again with GetBlindingData for explicit value and confidential
asset, we load the precomputed data with value = -1 and assert the
loaded value be the explicit value in the transaction. This is only true
for explicit value and explicit asset.
The changed assertion checks that written value should be same as the
explicit value that was written only when the amounts are valid
7f3a6a9495 wallet: Add external-signer-support specific error message (Hennadii Stepanov)
Pull request description:
On master (5f44c5c428) an attempt to load an external signer wallet using Bitcoin Core compiled without external signer support fails with the following log messages:
```
2022-02-20T19:01:11Z [qt-walletctrl] Using SQLite Version 3.31.1
2022-02-20T19:01:11Z [qt-walletctrl] Using wallet /home/hebasto/.bitcoin/testnet3/wallets/coldcard-0220
2022-02-20T19:01:11Z [qt-walletctrl] init message: Loading wallet…
2022-02-20T19:01:11Z [qt-walletctrl] [coldcard-0220] Error: External signer wallet being loaded without external signer support compiled
2022-02-20T19:01:11Z [qt-walletctrl] [coldcard-0220] Releasing wallet
```
While log messages are good, a message in the GUI window is completely misleading:
This PR fixes this issue:
ACKs for top commit:
achow101:
ACK 7f3a6a9495
kristapsk:
ACK 7f3a6a9495
brunoerg:
crACK 7f3a6a9495
Tree-SHA512: a4842751c0ca8a37ccc3ea00503678f6b712a7f53d6cbdc07ce02dcb85ca8a94890d1c2da20307be043faa347747abeba29185c88ba12edd5253bfca56531585
