fix: prevent unsigned underflow in FluidV1 swap routing functions#558
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sunce86 wants to merge 1 commit intopropeller-heads:mainfrom
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fix: prevent unsigned underflow in FluidV1 swap routing functions#558sunce86 wants to merge 1 commit intopropeller-heads:mainfrom
sunce86 wants to merge 1 commit intopropeller-heads:mainfrom
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swap_routing_in() and swap_routing_out() compute a subtraction that can produce a negative result when the debt pool offers better pricing. The Go reference (KyberSwap big.Int) handles this natively since big.Int is signed, and the caller checks a.Sign() <= 0 to route through debt. The Rust port used unsigned U256 subtraction which wraps on underflow, producing a large positive value that bypasses the debt routing path and incorrectly sends the swap through the collateral pool. Fix: use saturating_sub so underflow produces 0 instead of wrapping. The existing caller already treats a == 0 as "route through debt pool", so no caller changes are needed. Reference: KyberNetwork/kyberswap-dex-lib pool_simulator.go:273-307
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Summary
swap_routing_in()andswap_routing_out()use a subtraction that can produce a negative result when the debt pool offers better pricing than the collateral pool. The Go reference implementation (KyberSwap pool_simulator.go:273-307) uses*big.Int(signed), and the caller checksa.Sign() <= 0to route the entire trade through the debt pool.The Rust port uses
U256(unsigned), so the subtraction wraps around to a large positive number instead of going negative. The existing caller checksa == U256::ZERO || a == U256::MAXbut a wrapped value is neither — it falls through to the wrong branch and routes the trade through the collateral pool.Fix
Replace
-withsaturating_sub()in both functions. When the result would be negative, this produces0instead of wrapping. The existing caller already handlesa == U256::ZEROas "route through debt pool", so no caller changes are needed.Test plan