[Sls-sea-dls] SDLS EP GVCID Issues

[David Koisser (external)]

Hello everyone,

We noticed some more issues regarding the GVCID / MAPID. After checking, 
it turns out different standards have very different interpretations. I 
attached screenshots of the regarding sections of the blue books for your 
convenience.

The SDLS EP GVCID seems to be an aggregate of the longest defined versions 
of the respective fields. To my knowledge SDLS EP seems to be the only and 
first document, which specifically defines a (merged) GVCID. All other 
standards only define them as GVCID = TFVN + SCID + VCID & GMAPID = TFVN + 
SCID + VCID + MAPID (without sizes). In USLP the relation between old and 
new frames is defined, but only for Proximity-1 (see C1.1). I am not sure 
if this is more clearly explained somewhere else.

In SDLS EP I see two problems. First, there is no explanation or 
justification for the lengths. Second, this may possibly lead to severe 
bugs, e.g. overflowing a TM VCID bigger than what fits in the defined 3 
bits, like 16 bits in USLP or worse, 6 bits in TC (with identical TFVN as 
TM). Improper sanity checks here may even lead to security critical bugs.

Cheers,
David


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