[edjeffreys]

Potential fix for https://github.com/edjeffreys/nomad-tailscale-controller/security/code-scanning/2

In general, to fix this class of issue you must ensure that any integer value parsed from a string (especially with strconv.Atoi returning an int) is either (a) parsed directly into the target-sized type using strconv.ParseInt/ParseUint with an appropriate bit size, or (b) range-checked before converting to a smaller-width type. For ports, the valid range is 0–65535, and typically 1–65535 (disallowing zero) for externally visible services.

For this specific case, the best fix with minimal behavioral change is to add an explicit upper-bound (and optionally lower-bound) check before converting svc.Port to uint16 in buildServeConfig. We already default zero ports to 443, so it's reasonable to only accept non-negative ports up to math.MaxUint16 (which is 65535) and treat anything else as invalid, falling back to 443. This prevents wraparound when converting to uint16 without changing the public API or the structure of Service.

Concretely:

• Edit internal/tailscale/client.go, inside buildServeConfig.
• Above the loop (after cfg := &ServeConfig{...}), define a local const defaultPort = uint16(443) to keep the default consistent and typed correctly, or just use uint16(443) inline.
• Replace port := uint16(svc.Port) and its if port == 0 { port = 443 } with logic that:
  • Starts with port := uint16(443) (the default).
  • If svc.Port is > 0 and svc.Port <= math.MaxUint16, set port = uint16(svc.Port).
• Import math at the top of internal/tailscale/client.go to access math.MaxUint16.

This ensures that any out-of-range or zero port results in a safe default (443), and any valid port (1–65535) is preserved, while eliminating the unsafe narrowing conversion.

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