shred_fetch: enforce fixed fec sets#7728
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## master #7728 +/- ##
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Coverage 83.0% 83.0%
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Files 812 812
Lines 356934 357178 +244
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+ Hits 296535 296814 +279
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AshwinSekar
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Aug 27, 2025
| recvr_stats: Option<Arc<StreamerReceiveStats>>, | ||
| sendr: EvictingSender<PacketBatch>, | ||
| bank_forks: &RwLock<BankForks>, | ||
| sharable_banks: &SharableBanks, |
AshwinSekar
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Aug 27, 2025
| return true; | ||
| }; | ||
| let Some(fec_set_index) = layout::get_fec_set_index(shred) else { | ||
| stats.fec_set_index_bad_deserialize += 1; |
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these deserialize failures are already thrown out when we parse the shred in sigverify, this just moves it up - shouldn't be a consensus altering change no need to feature flag.
| /// all erasure sets contain exactly `DATA_SHREDS_PER_FEC_BLOCK` data and coding shreds: | ||
| /// - `index` is between `fec_set_index` and `fec_set_index + DATA_SHREDS_PER_FEC_BLOCK` | ||
| /// - `fec_set_index` is a multiple of `DATA_SHREDS_PER_FEC_BLOCK` | ||
| pub fn check_fixed_fec_set(index: u32, fec_set_index: u32) -> bool { |
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should we not have this together with basic shred format validation outside of blockstore code?
| /// Note: this check is critical to verify that the last fec set is sufficiently sized. | ||
| /// This currently is checked post insert in `Blockstore::check_last_fec_set`, but in the | ||
| /// future it can be solely checked during ingest | ||
| pub fn check_last_data_shred_index(index: u32) -> bool { |
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this also might be better suited inside shred.rs or similar.
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Thank you, this looks great, left a couple of small nits |
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alexpyattaev
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LGTM but please let @bw-solana also take a second look before merging.
This was referenced Sep 4, 2025
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Problem
See solana-foundation/solana-improvement-documents#317 for more details.
We wish to enforce that each FEC set has exactly 32 data and 32 coding shreds.
Summary of Changes
As outlined in the SIMD, we ignore any shreds that do not meet the index/fec_set_index requirements on ingest.
Specifically ensure that:
fec_set_indexis a multiple of 32fec_set_index <= index < fec_set_index + 32LAST_SHRED_IN_SLOTdata shred index must be== 31 (mod 32)ErasureConfigon all coding shreds must specify 32:32Note: this is a shred feature flag so it takes effect 1 epoch after normal feature activation
An alternate approach considered was performing the verification after ingest and marking the block as dead:
Some follow up work after FF activation:
fec_set_index,ErasureConfig, andproof_sizefrom shred headers.