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Use saturating math for reserve and LSPS amounts - #1185
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Setting AnchorChannelsConfig::per_channel_reserve_sats to u64::MAX is a natural way to say "never open or accept anchor channels with untrusted peers", since no wallet can cover that reserve. However, the reserve sums used unchecked arithmetic: multiplying it by the number of existing anchor channels, or adding the reserve for a new channel, overflowed and panicked in debug builds. Values close to a power of two could also wrap to a tiny reserve in release builds. Use saturating arithmetic so an oversized reserve is treated as unsatisfiable instead. This was found by Project Loupe. This change was made with the help of Claude Code.
The LSPS2 service computed the JIT channel size by multiplying the intercepted HTLC amount by the configured over-provisioning rate, and the LSPS1 client summed the caller-provided channel balances, both with unchecked arithmetic. Oversized inputs overflowed, panicking in debug builds and wrapping to a bogus channel size in release builds. Use saturating arithmetic so such inputs fall through to the existing insufficient-funds and LSP-limit checks. This was found by Project Loupe. This change was made with the help of Claude Code.
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Some reserve and channel size calculations used unchecked math. Large
inputs, such as
per_channel_reserve_sats = u64::MAX, panic in debugbuilds and can wrap in release builds.
Use saturating math so these hit the normal insufficient-funds checks
instead.
Found by Project Loupe.