6f732ffc3c
32a9f13cb805ecf6aebb5cf4e5d92b8a47c4548b wallet: avoid returning a reference to vMasterKey after releasing the mutex that guards it (Vasil Dimov)
Pull request description:
`CWallet::GetEncryptionKey()` would return a reference to the internal
`CWallet::vMasterKey`, guarded by `CWallet::cs_wallet`, which is unsafe.
Returning a copy would be a shorter solution, but could have security
implications of the master key remaining somewhere in the memory even
after `CWallet::Lock()` (the current calls to
`CWallet::GetEncryptionKey()` are safe, but that is not future proof).
So, instead of `EncryptSecret(m_storage.GetEncryptionKey(), ...)`
change the `GetEncryptionKey()` method to provide the encryption
key to a given callback:
`m_storage.WithEncryptionKey([](const CKeyingMaterial& k) { EncryptSecret(k, ...); })`
This silences the following (clang 18):
```
wallet/wallet.cpp:3520:12: error: returning variable 'vMasterKey' by reference requires holding mutex 'cs_wallet' [-Werror,-Wthread-safety-reference-return]
3520 | return vMasterKey;
| ^
```
---
_Previously this PR modified both ArgsManager and wallet code. But the ArgsManager commit 856c88776f was merged in https://github.com/bitcoin/bitcoin/pull/29040 so now this only affects wallet code. The previous PR description was:_
Avoid this unsafe pattern from `ArgsManager` and `CWallet`:
```cpp
class A
{
Mutex mutex;
Foo member GUARDED_BY(mutex);
const Foo& Get()
{
LOCK(mutex);
return member;
} // callers of `Get()` will have access to `member` without owning the mutex.
```
ACKs for top commit:
achow101:
ACK 32a9f13cb805ecf6aebb5cf4e5d92b8a47c4548b
ryanofsky:
Code review ACK 32a9f13cb805ecf6aebb5cf4e5d92b8a47c4548b. This seems like a potentially real race condition, and the fix here is pretty simple.
furszy:
ACK 32a9f13c
Tree-SHA512: 133da84691642afc1a73cf14ad004a7266cb4be1a6a3ec634d131dca5dbcdef52522c1d5eb04f5b6c4e06e1fc3e6ac57315f8fe1e207b464ca025c2b4edefdc1
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