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fix: avoid UInt32 underflow sizing the address allocator for small subnets #1864

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fix: avoid UInt32 underflow sizing the address allocator for small subnets #1864

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11 changes: 10 additions & 1 deletion Sources/Services/Network/Server/DefaultNetworkService.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,16 @@ public actor DefaultNetworkService: NetworkService {
}

let subnet = status.ipv4Subnet
let size = Int(subnet.upper.value - subnet.lower.value - 3)
// Widen to Int before subtracting: doing the arithmetic in UInt32 traps
// on underflow when the subnet is too small (e.g. a /31 where
// upper - lower < 3).
let size = Int(subnet.upper.value) - Int(subnet.lower.value) - 3
guard size > 0 else {
throw ContainerizationError(
.invalidState,
message: "network \(network.id) subnet is too small to allocate addresses"
)
}
self.network = network
self.log = log
self.allocator = try AttachmentAllocator(lower: subnet.lower.value + 2, size: size)
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