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fix: implement overflow-safe per-byte gas multiplication #25443

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fix: implement overflow-safe per-byte gas multiplication #25443

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34 changes: 26 additions & 8 deletions store/gaskv/store.go
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Original file line number Diff line number Diff line change
@@ -1,9 +1,11 @@
package gaskv

import (
"io"
"io"
"math"
"math/bits"

"cosmossdk.io/store/types"
"cosmossdk.io/store/types"
)

var _ types.KVStore = &Store{}
Expand Down Expand Up @@ -38,8 +40,8 @@ func (gs *Store) Get(key []byte) (value []byte) {
value = gs.parent.Get(key)

// TODO overflow-safe math?
gs.gasMeter.ConsumeGas(gs.gasConfig.ReadCostPerByte*types.Gas(len(key)), types.GasReadPerByteDesc)
gs.gasMeter.ConsumeGas(gs.gasConfig.ReadCostPerByte*types.Gas(len(value)), types.GasReadPerByteDesc)
gs.gasMeter.ConsumeGas(safeMulGasPerByte(gs.gasConfig.ReadCostPerByte, len(key)), types.GasReadPerByteDesc)
gs.gasMeter.ConsumeGas(safeMulGasPerByte(gs.gasConfig.ReadCostPerByte, len(value)), types.GasReadPerByteDesc)

return value
}
Expand All @@ -50,8 +52,8 @@ func (gs *Store) Set(key, value []byte) {
types.AssertValidValue(value)
gs.gasMeter.ConsumeGas(gs.gasConfig.WriteCostFlat, types.GasWriteCostFlatDesc)
// TODO overflow-safe math?
gs.gasMeter.ConsumeGas(gs.gasConfig.WriteCostPerByte*types.Gas(len(key)), types.GasWritePerByteDesc)
gs.gasMeter.ConsumeGas(gs.gasConfig.WriteCostPerByte*types.Gas(len(value)), types.GasWritePerByteDesc)
gs.gasMeter.ConsumeGas(safeMulGasPerByte(gs.gasConfig.WriteCostPerByte, len(key)), types.GasWritePerByteDesc)
gs.gasMeter.ConsumeGas(safeMulGasPerByte(gs.gasConfig.WriteCostPerByte, len(value)), types.GasWritePerByteDesc)
gs.parent.Set(key, value)
}

Expand Down Expand Up @@ -121,6 +123,22 @@ func newGasIterator(gasMeter types.GasMeter, gasConfig types.GasConfig, parent t
}
}

// safeMulGasPerByte multiplies a per-byte gas cost by a length using
// overflow-safe semantics. If the 64-bit multiplication would overflow,
// it returns math.MaxUint64 so the downstream GasMeter can handle it
// consistently (e.g. saturate or panic per implementation).
func safeMulGasPerByte(perByte types.Gas, length int) types.Gas {
if length <= 0 {
return 0
}

lo, hi := bits.Mul64(uint64(perByte), uint64(length))
if hi != 0 {
return types.Gas(math.MaxUint64)
}
return types.Gas(lo)
}

// Domain implements Iterator, getting the underlying iterator's domain.
func (gi *gasIterator) Domain() (start, end []byte) {
return gi.parent.Domain()
Expand Down Expand Up @@ -170,8 +188,8 @@ func (gi *gasIterator) consumeSeekGas() {
key := gi.Key()
value := gi.Value()

gi.gasMeter.ConsumeGas(gi.gasConfig.ReadCostPerByte*types.Gas(len(key)), types.GasValuePerByteDesc)
gi.gasMeter.ConsumeGas(gi.gasConfig.ReadCostPerByte*types.Gas(len(value)), types.GasValuePerByteDesc)
gi.gasMeter.ConsumeGas(safeMulGasPerByte(gi.gasConfig.ReadCostPerByte, len(key)), types.GasValuePerByteDesc)
gi.gasMeter.ConsumeGas(safeMulGasPerByte(gi.gasConfig.ReadCostPerByte, len(value)), types.GasValuePerByteDesc)
}
gi.gasMeter.ConsumeGas(gi.gasConfig.IterNextCostFlat, types.GasIterNextCostFlatDesc)
}