Use floor when computing max value of a path, not ceil
#3755
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👋 I see @jkczyz was un-assigned. |
When calculating the maximum contribution of a path to a larger route, we want to ensure we don't overshoot as that might cause us to violate a maximum value limit. In 209cb2a, we started by calculating with `ceil`, which can trigger exactly that, so here we drop the extra addition, switching us to `floor`. Found both by the `router` fuzzer as well as the `generate_large_mpp_routes` test.
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tnull
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TheBlueMatt
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Assigned val since it was her pr. |
valentinewallace
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Backported in #3757 |
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v0.1.3 - Apr 30, 2025 - "Routing Unicode in 2025" Bug Fixes ========= * `Event::InvoiceReceived` is now only generated once for each `Bolt12Invoice` received matching a pending outbound payment. Previously it would be provided each time we received an invoice, which may happen many times if the sender sends redundant messages to improve success rates (lightningdevkit#3658). * LDK's router now more fully saturates paths which are subject to HTLC maximum restrictions after the first hop. In some rare cases this can result in finding paths when it would previously spuriously decide it cannot find enough diverse paths (lightningdevkit#3707, lightningdevkit#3755). Security ======== 0.1.3 fixes a denial-of-service vulnerability which cause a crash of an LDK-based node if an attacker has access to a valid `Bolt12Offer` which the LDK-based node created. * A malicious payer which requests a BOLT 12 Invoice from an LDK-based node (via the `Bolt12InvoiceRequest` message) can cause the panic of the LDK-based node due to the way `String::truncate` handles UTF-8 codepoints. The codepath can only be reached once the received `Botlt12InvoiceRequest` has been authenticated to be based on a valid `Bolt12Offer` which the same LDK-based node issued (lightningdevkit#3747, lightningdevkit#3750).
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When calculating the maximum contribution of a path to a larger route, we want to ensure we don't overshoot as that might cause us to violate a maximum value limit.
In 209cb2a, we started by calculating with
ceil, which can trigger exactly that, so here we drop the extra addition, switching us tofloor.Fixes #3707