fix(unikernels): reject non-contiguous subnet masks in subnetMaskToCIDR - #950
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subnetMaskToCIDR() computed the prefix length by counting set bits without checking for contiguity. As a result, non-contiguous masks like 255.0.255.0 were accepted as /16. Refactor subnetMaskToCIDR() using net.ParseIP and net.IPMask.Size() to validate both mask format and contiguity. Add comprehensive unit tests covering canonical, non-contiguous, and malformed masks. Fixes urunc-dev#909 Signed-off-by: Harsha Vardhan <harshahvk2005@gmail.com>
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Fixes #909
Summary
subnetMaskToCIDR()inpkg/unikontainers/unikernels/utils.gopreviously computed the prefix length by counting set bits without verifying contiguity. As a result, structurally invalid non-contiguous subnet masks (such as255.0.255.0or0.255.255.255) were silently accepted and mapped to incorrect CIDR prefix lengths instead of being rejected.Solution
subnetMaskToCIDR()to parse the subnet mask usingnet.ParseIP()and validate contiguity vianet.IPMask.Size(). Non-contiguous masks causemask.Size()to return(0, 0), which is now detected and returned as a validation error (invalid (non-contiguous) subnet mask).utils_test.gocovering canonical masks (/0to/32), non-contiguous masks, and malformed string inputs.