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Merge bitcoin/bitcoin#25595: Verify PSBT inputs rather than check for fields being empty #1222

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Merge bitcoin/bitcoin#25595: Verify PSBT inputs rather than check for fields being empty #1222

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2 changes: 1 addition & 1 deletion src/node/psbt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ PSBTAnalysis AnalyzePSBT(PartiallySignedTransaction psbtx)
}

// Check if it is final
if (!utxo.IsNull() && !PSBTInputSigned(input)) {
if (!PSBTInputSignedAndVerified(psbtx, i, &txdata)) {
input_analysis.is_final = false;

// Figure out what is missing
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29 changes: 28 additions & 1 deletion src/psbt.cpp
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Expand Up @@ -181,6 +181,33 @@ void PSBTOutput::Merge(const PSBTOutput& output)
if (redeem_script.empty() && !output.redeem_script.empty()) redeem_script = output.redeem_script;
}

bool PSBTInputSignedAndVerified(const PartiallySignedTransaction psbt, unsigned int input_index, const PrecomputedTransactionData* txdata)
{
CTxOut utxo;
assert(psbt.inputs.size() >= input_index);
const PSBTInput& input = psbt.inputs[input_index];

if (input.non_witness_utxo) {
// If we're taking our information from a non-witness UTXO, verify that it matches the prevout.
COutPoint prevout = psbt.tx->vin[input_index].prevout;
if (prevout.n >= input.non_witness_utxo->vout.size()) {
return false;
}
if (input.non_witness_utxo->GetHash() != prevout.hash) {
return false;
}
utxo = input.non_witness_utxo->vout[prevout.n];
} else {
return false;
}

if (txdata) {
return VerifyScript(input.final_script_sig, utxo.scriptPubKey, STANDARD_SCRIPT_VERIFY_FLAGS, MutableTransactionSignatureChecker{&(*psbt.tx), input_index, utxo.nValue, *txdata, MissingDataBehavior::FAIL});
} else {
return VerifyScript(input.final_script_sig, utxo.scriptPubKey, STANDARD_SCRIPT_VERIFY_FLAGS, MutableTransactionSignatureChecker{&(*psbt.tx), input_index, utxo.nValue, MissingDataBehavior::FAIL});
}
}
Comment on lines +184 to +209
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@coderabbitai coderabbitai bot Dec 6, 2025

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⚠️ Potential issue | 🔴 Critical

Critical: Off-by-one error in bounds assertion.

Line 187 uses >= which allows input_index == psbt.inputs.size(), but the subsequent access at line 188 would be out-of-bounds.

Apply this diff to fix the assertion:

-    assert(psbt.inputs.size() >= input_index);
+    assert(input_index < psbt.inputs.size());

Additionally, as noted in the header review, the function signature passes psbt by value which is inefficient. Consider using const PartiallySignedTransaction& psbt instead.

🤖 Prompt for AI Agents 
In src/psbt.cpp around lines 184 to 209, the bounds assertion is inverted and
allows an out-of-range access; change the assertion to ensure input_index is
strictly less than psbt.inputs.size() (e.g. assert(input_index <
psbt.inputs.size())) and update the function signature to take the PSBT by const
reference (const PartiallySignedTransaction& psbt) to avoid unnecessary copying;
make corresponding symbol/name adjustments in the function body if needed.


size_t CountPSBTUnsignedInputs(const PartiallySignedTransaction& psbt) {
size_t count = 0;
for (const auto& input : psbt.inputs) {
Expand Down Expand Up @@ -238,7 +265,7 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
PSBTInput& input = psbt.inputs.at(index);
const CMutableTransaction& tx = *psbt.tx;

if (PSBTInputSigned(input)) {
if (PSBTInputSignedAndVerified(psbt, index, txdata)) {
return true;
}

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5 changes: 4 additions & 1 deletion src/psbt.h
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Expand Up @@ -865,9 +865,12 @@ std::string PSBTRoleName(PSBTRole role);
/** Compute a PrecomputedTransactionData object from a psbt. */
PrecomputedTransactionData PrecomputePSBTData(const PartiallySignedTransaction& psbt);

/** Checks whether a PSBTInput is already signed. */
/** Checks whether a PSBTInput is already signed by checking for non-null finalized fields. */
bool PSBTInputSigned(const PSBTInput& input);

/** Checks whether a PSBTInput is already signed by doing script verification using final fields. */
bool PSBTInputSignedAndVerified(const PartiallySignedTransaction psbt, unsigned int input_index, const PrecomputedTransactionData* txdata);

/** Signs a PSBTInput, verifying that all provided data matches what is being signed.
*
* txdata should be the output of PrecomputePSBTData (which can be shared across
Expand Down
1 change: 1 addition & 0 deletions test/functional/rpc_psbt.py
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Expand Up @@ -504,5 +504,6 @@ def test_psbt_input_keys(psbt_input, keys):
self.log.info("Test we don't crash when making a 0-value funded transaction at 0 fee without forcing an input selection")
assert_raises_rpc_error(-4, "Transaction requires one destination of non-0 value, a non-0 feerate, or a pre-selected input", self.nodes[0].walletcreatefundedpsbt, [], [{"data": "deadbeef"}], 0, {"fee_rate": "0"})


if __name__ == '__main__':
PSBTTest().main()
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