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Add new gossip rule to REJECT sidecars with index >= MAX_BLOBS_PER_BLOCK #3525

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Oct 18, 2023
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Add new gossip rule to REJECT sidecars with index >= MAX_BLOBS_PER_BLOCK #3525

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Add new gossip rule to `REJECT` sidecars with index >= MAX_BLOBS_PER_…
tbenr Oct 18, 2023
a2d021d
re-order conditions
djrtwo Oct 18, 2023
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1 change: 1 addition & 0 deletions specs/deneb/p2p-interface.md
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Expand Up @@ -148,6 +148,7 @@ This topic is used to propagate signed blob sidecars, where each blob index maps

The following validations MUST pass before forwarding the `signed_blob_sidecar` on the network, assuming the alias `sidecar = signed_blob_sidecar.message`:

- _[REJECT]_ The sidecar's index is consistent with `MAX_BLOBS_PER_BLOCK` -- i.e. `sidecar.index < MAX_BLOBS_PER_BLOCK`.
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actualy the previous check itself assures that this is not unbounded : compute_subnet_for_blob_sidecar(sidecar.index) == subnet_id so this is a redundant check

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@StefanBratanov StefanBratanov Oct 18, 2023 •
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Not true though because compute_subnet_for_blob_sidecar calculates the subnet_id using mod BLOB_SIDECAR_SUBNET_COUNT, so for example for subnet 4 and index 100, compute_subnet_for_blob_sidecar(100) == 4 thus valid according to the rule.

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@g11tech g11tech Oct 18, 2023 •
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ahh in that case do we want it to be hardfork independent MAX_BLOB_COMMITMENTS_PER_BLOCK or MAX_BLOBS_PER_BLOCK? (although the tighter bound of max blobs per block makes sense)

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I believe @tbenr and @StefanBratanov are correct and that this should be bounded

There is an equivalent condition for beacon_attestation subnets here -- https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/p2p-interface.md#beacon_attestation_subnet_id

REJECT] The committee index is within the expected range -- i.e. data.index < get_committee_count_per_slot(state, data.target.epoch)

I would argue that this should be the first condition -- before the second condition that calls compute_subnet_for_blob_side_car. Tossing out junk first (and mirroring the order in the attestation subnet)

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@tbenr tbenr Oct 19, 2023 •
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I would argue that this should be the first condition ...

True, we could save the function call but currently computes just a modulo.
Teku will perform this in this order in any case because we do the subnet_id check closer to the networking layer and the actual gossip validation runs on top of it.

- _[REJECT]_ The sidecar is for the correct subnet -- i.e. `compute_subnet_for_blob_sidecar(sidecar.index) == subnet_id`.
- _[IGNORE]_ The sidecar is not from a future slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) -- i.e. validate that `sidecar.slot <= current_slot` (a client MAY queue future sidecars for processing at the appropriate slot).
- _[IGNORE]_ The sidecar is from a slot greater than the latest finalized slot -- i.e. validate that `sidecar.slot > compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)`
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