slow: Add OSSP support

[corubba]

Add basic printing of "Organization Specific Slow Protocol" (OSSP), which is standardized in IEEE 802.3 Annex 57B. Since this is used for non-standardized protocols and thus carries mostly unknown-structured data, most of the packet is still printed verbatim.

Also add the OUI of ITU-T that is used as part of its "Ethernet synchronization messaging channel" (ESMC) protocol, which is based on OSSP.

[infrastation]

As far as I can see, this line can cause an out-of-bounds read: neither slow_ossp_print() nor its caller ensure that here tlen >= 3. Please add a length check.

[corubba]

GET_BE_U_3 does a length check, and will not return if there is not enough data. You can find the same pattern in other protocols, for example here, here and here. Worked fine when I tested it reducing the packet step by step one byte at a time.

[infrastation]

In this context the GET_ macros guard the boundaries of the actually present (captured) data, and tlen is the declared data length. Please note:

• the ND_ICHECK_U(len, <, 8); just before the data fetch in the first example,
• the if (subtlv_len >= 6) around the data fetch in the second example, and
• the if (len < length * NSH_HDR_WORD_SIZE) before the data fetch in the third example.

[corubba]

I don't really understand how tlen could ever be less than the captured data (the other way around sure), and thus tlen < 3 not always first trigger the GET_BE_U_3 longjump. But I will assume you know better and submit to your judgement.

[corubba]

I guess the reason is to have the correct message in the output, truncated packet (due to snaplen) vs invalid packet (simply too short).