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910e897c54
## Why this should be merged The `vm.PrecompileEnvironment.Call()` method requires careful usage because of reentrancy vulnerabilities (this is common to all outgoing `CALL`s in the EVM, not just stateful precompiles). This package provides a common method of protection, a reentrancy guard. ## How this works Provides a function that returns `vm.ErrExecutionReverted` if called twice, by the same contract, in the same transaction, with the same identifier. ## How this was tested Unit and integration tests.
55 lines
2.2 KiB
Go
55 lines
2.2 KiB
Go
// Copyright 2025 the libevm authors.
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//
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// The libevm additions to go-ethereum are free software: you can redistribute
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// them and/or modify them under the terms of the GNU Lesser General Public License
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// as published by the Free Software Foundation, either version 3 of the License,
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// or (at your option) any later version.
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//
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// The libevm additions are distributed in the hope that they will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
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// General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see
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// <http://www.gnu.org/licenses/>.
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// Package reentrancy provides a reentrancy guard for stateful precompiles that
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// make outgoing calls to other contracts.
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//
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// Reentrancy occurs when the contract (C) called by a precompile (P) makes a
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// further call back into P, which may result in theft of funds (see DAO hack).
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// A reentrancy guard detects these recursive calls and reverts.
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package reentrancy
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import (
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"github.com/ava-labs/libevm/common"
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"github.com/ava-labs/libevm/core/vm"
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"github.com/ava-labs/libevm/crypto"
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"github.com/ava-labs/libevm/libevm"
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)
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var slotPreimagePrefix = []byte("libevm-reentrancy-guard-")
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// Guard returns [vm.ErrExecutionReverted] i.f.f. it has already been called
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// with the same `key`, by the same contract, in the same transaction. It
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// otherwise returns nil. The `key` MAY be nil.
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//
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// Contract equality is defined as the [libevm.AddressContext] "self" address
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// being the same under EVM semantics.
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func Guard(env vm.PrecompileEnvironment, key []byte) error {
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self := env.Addresses().EVMSemantic.Self
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slot := crypto.Keccak256Hash(slotPreimagePrefix, key)
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sdb := env.StateDB()
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if sdb.GetTransientState(self, slot) != (common.Hash{}) {
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return vm.ErrExecutionReverted
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}
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sdb.SetTransientState(self, slot, common.Hash{1})
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return nil
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}
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// Keep the `libevm` import to allow the linked comment on [Guard]. The package
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// is imported by `vm` anyway so this is a noop but it improves developer
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// experience.
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var _ = (*libevm.AddressContext)(nil)
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