Merge #18487: rpc: Fix rpcRunLater race in walletpassphrase

7b8e157 rpc: Fix rpcRunLater race in walletpassphrase (João Barbosa)

Pull request description:

  Release locks before calling `rpcRunLater`.

  Quick explanation: `rpcRunLater` leads to `event_free` which calls `event_del` which can wait for the event callback to finish if it's already running and that callback will try to lock wallet mutex - which is already locked in http thread.

  Fixes #14995 , fixes #18482. Best reviewed with whitespace changes hidden.

ACKs for top commit:
  MarcoFalke:
    ACK 7b8e157, only tested that this avoids the node freezing. Did not look at how libevent works or how the deadlock happens or if this breaks other stuff. 📞
  ryanofsky:
    Code review ACK 7b8e157. Just updated comment since last review

Tree-SHA512: 17874a2fa7b0e164fb0d7ee4cb7d59650275b8c03476fb291d60af8b758495457660d3912623fb26259fefe84aeba21c0a9e0c6467982ba511f19344ed5413ab

Author: laanwj

src/wallet/rpcwallet.cpp

@@ -1912,44 +1912,52 @@ static UniValue walletpassphrase(const JSONRPCRequest& request)
                 },
             }.Check(request);
 
-    auto locked_chain = pwallet->chain().lock();
-    LOCK(pwallet->cs_wallet);
-
-    if (!pwallet->IsCrypted()) {
-        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrase was called.");
-    }
+    int64_t nSleepTime;
+    {
+        auto locked_chain = pwallet->chain().lock();
+        LOCK(pwallet->cs_wallet);
 
-    // Note that the walletpassphrase is stored in request.params[0] which is not mlock()ed
-    SecureString strWalletPass;
-    strWalletPass.reserve(100);
-    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
-    // Alternately, find a way to make request.params[0] mlock()'d to begin with.
-    strWalletPass = request.params[0].get_str().c_str();
+        if (!pwallet->IsCrypted()) {
+            throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrase was called.");
+        }
 
-    // Get the timeout
-    int64_t nSleepTime = request.params[1].get_int64();
-    // Timeout cannot be negative, otherwise it will relock immediately
-    if (nSleepTime < 0) {
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "Timeout cannot be negative.");
-    }
-    // Clamp timeout
-    constexpr int64_t MAX_SLEEP_TIME = 100000000; // larger values trigger a macos/libevent bug?
-    if (nSleepTime > MAX_SLEEP_TIME) {
-        nSleepTime = MAX_SLEEP_TIME;
-    }
+        // Note that the walletpassphrase is stored in request.params[0] which is not mlock()ed
+        SecureString strWalletPass;
+        strWalletPass.reserve(100);
+        // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+        // Alternately, find a way to make request.params[0] mlock()'d to begin with.
+        strWalletPass = request.params[0].get_str().c_str();
+
+        // Get the timeout
+        nSleepTime = request.params[1].get_int64();
+        // Timeout cannot be negative, otherwise it will relock immediately
+        if (nSleepTime < 0) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Timeout cannot be negative.");
+        }
+        // Clamp timeout
+        constexpr int64_t MAX_SLEEP_TIME = 100000000; // larger values trigger a macos/libevent bug?
+        if (nSleepTime > MAX_SLEEP_TIME) {
+            nSleepTime = MAX_SLEEP_TIME;
+        }
 
-    if (strWalletPass.empty()) {
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "passphrase can not be empty");
-    }
+        if (strWalletPass.empty()) {
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "passphrase can not be empty");
+        }
 
-    if (!pwallet->Unlock(strWalletPass)) {
-        throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
-    }
+        if (!pwallet->Unlock(strWalletPass)) {
+            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
+        }
 
-    pwallet->TopUpKeyPool();
+        pwallet->TopUpKeyPool();
 
-    pwallet->nRelockTime = GetTime() + nSleepTime;
+        pwallet->nRelockTime = GetTime() + nSleepTime;
+    }
 
+    // rpcRunLater must be called without cs_wallet held otherwise a deadlock
+    // can occur. The deadlock would happen when RPCRunLater removes the
+    // previous timer (and waits for the callback to finish if already running)
+    // and the callback locks cs_wallet.
+    AssertLockNotHeld(wallet->cs_wallet);
     // Keep a weak pointer to the wallet so that it is possible to unload the
     // wallet before the following callback is called. If a valid shared pointer
     // is acquired in the callback then the wallet is still loaded.