LINKTYPE_NFLOG: Fix size of hardware address structure padding. #48
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It is two octets, not one octet, to pad to a 32-bit boundary. That matches observed captures, and also see: https://github.com/torvalds/linux/blob/master/include/uapi/linux/netfilter/nfnetlink_log.h#L27 https://github.com/the-tcpdump-group/libpcap/blob/master/pcap/nflog.h#L64 Signed-off-by: John Thacker <johnthacker@gmail.com>
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The address field does not look consistent either: it says "8 Octets, including padding", but both of the linked C structures show it as an array of 8 bytes. tcpdump NFLOG decoder declares it as 8 bytes too, although it does not seem to decode hardware addresses. |
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In my sample captures, it's always 8 bytes, and (since it's usually an Ethernet EUI-48 address) the "Address Length" field has the value 6, there are two bytes of padding, then the "Address" field has 6 bytes for the address and two more bytes of padding within that field. Presumably for a EUI-64 address there would be no padding in the 8-byte Address field. |
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So I think the Address field is "8 Octets, truncated or padded with zeroes as necessary." Procrustean. |
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Thank you. |
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Nov 23, 2025
Based on additional comments by John Thacker in pull request #48. [skip ci]
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It is two octets, not one octet, to pad to a 32-bit boundary. That matches observed captures, and also see:
https://github.com/torvalds/linux/blob/master/include/uapi/linux/netfilter/nfnetlink_log.h#L27
https://github.com/the-tcpdump-group/libpcap/blob/master/pcap/nflog.h#L64