Guard against no attesters within committee in VerifyAttestationNoVerifySignature (#15169)

* Guard against no attesters within committee in `VerifyAttestationNoVerifySignature`

* changelog fragment

beacon-chain/core/blocks/attestation.go

@@ -106,7 +106,7 @@ func VerifyAttestationNoVerifySignature(
 	if err != nil {
 		return err
 	}
-	c := helpers.SlotCommitteeCount(activeValidatorCount)
+	committeeCount := helpers.SlotCommitteeCount(activeValidatorCount)
 
 	var indexedAtt ethpb.IndexedAtt
 
@@ -115,13 +115,14 @@ func VerifyAttestationNoVerifySignature(
 			return errors.New("committee index must be 0 post-Electra")
 		}
 
+		aggBits := att.GetAggregationBits()
 		committeeIndices := att.CommitteeBitsVal().BitIndices()
 		committees := make([][]primitives.ValidatorIndex, len(committeeIndices))
 		participantsCount := 0
 		var err error
 		for i, ci := range committeeIndices {
-			if uint64(ci) >= c {
+			if uint64(ci) >= committeeCount {
-				return fmt.Errorf("committee index %d >= committee count %d", ci, c)
+				return fmt.Errorf("committee index %d >= committee count %d", ci, committeeCount)
 			}
 			committees[i], err = helpers.BeaconCommitteeFromState(ctx, beaconState, att.GetData().Slot, primitives.CommitteeIndex(ci))
 			if err != nil {
@@ -129,16 +130,32 @@ func VerifyAttestationNoVerifySignature(
 			}
 			participantsCount += len(committees[i])
 		}
-		if att.GetAggregationBits().Len() != uint64(participantsCount) {
+		if aggBits.Len() != uint64(participantsCount) {
 			return fmt.Errorf("aggregation bits count %d is different than participant count %d", att.GetAggregationBits().Len(), participantsCount)
 		}
+
+		committeeOffset := 0
+		for ci, c := range committees {
+			attesterFound := false
+			for i := range c {
+				if aggBits.BitAt(uint64(committeeOffset + i)) {
+					attesterFound = true
+					break
+				}
+			}
+			if !attesterFound {
+				return fmt.Errorf("no attesting indices found for committee index %d", ci)
+			}
+			committeeOffset += len(c)
+		}
+
 		indexedAtt, err = attestation.ConvertToIndexed(ctx, att, committees...)
 		if err != nil {
 			return err
 		}
 	} else {
-		if uint64(att.GetData().CommitteeIndex) >= c {
+		if uint64(att.GetData().CommitteeIndex) >= committeeCount {
-			return fmt.Errorf("committee index %d >= committee count %d", att.GetData().CommitteeIndex, c)
+			return fmt.Errorf("committee index %d >= committee count %d", att.GetData().CommitteeIndex, committeeCount)
 		}
 
 		// Verify attesting indices are correct.

beacon-chain/core/blocks/attestation_test.go

@@ -296,6 +296,22 @@ func TestVerifyAttestationNoVerifySignature_Electra(t *testing.T) {
 		err = blocks.VerifyAttestationNoVerifySignature(context.TODO(), beaconState, att)
 		assert.ErrorContains(t, "aggregation bits count 123 is different than participant count 3", err)
 	})
+	t.Run("no attester in committee", func(t *testing.T) {
+		aggBits := bitfield.NewBitlist(3)
+		committeeBits := bitfield.NewBitvector64()
+		committeeBits.SetBitAt(0, true)
+		att := &ethpb.AttestationElectra{
+			Data: &ethpb.AttestationData{
+				Source: &ethpb.Checkpoint{Epoch: 0, Root: mockRoot[:]},
+				Target: &ethpb.Checkpoint{Epoch: 0, Root: make([]byte, 32)},
+			},
+			AggregationBits: aggBits,
+			CommitteeBits:   committeeBits,
+		}
+		att.Signature = zeroSig[:]
+		err = blocks.VerifyAttestationNoVerifySignature(context.TODO(), beaconState, att)
+		assert.ErrorContains(t, "no attesting indices found for committee index 0", err)
+	})
 }
 
 func TestConvertToIndexed_OK(t *testing.T) {

changelog/radek_electra-committee-assertion.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Guard against no attesters within committee in `VerifyAttestationNoVerifySignature`.

proto/prysm/v1alpha1/attestation/attestation_utils.go

@@ -111,7 +111,7 @@ func AttestingIndices(att ethpb.Att, committees ...[]primitives.ValidatorIndex)
 
 	attesters := make([]uint64, 0, aggBits.Count())
 	committeeOffset := 0
-	for _, c := range committees {
+	for ci, c := range committees {
 		committeeAttesters := make([]uint64, 0, len(c))
 		for i, vi := range c {
 			if aggBits.BitAt(uint64(committeeOffset + i)) {
@@ -119,7 +119,7 @@ func AttestingIndices(att ethpb.Att, committees ...[]primitives.ValidatorIndex)
 			}
 		}
 		if len(committeeAttesters) == 0 {
-			return nil, fmt.Errorf("no attesting indices found in committee %v", c)
+			return nil, fmt.Errorf("no attesting indices found for committee index %d", ci)
 		}
 		attesters = append(attesters, committeeAttesters...)
 		committeeOffset += len(c)

proto/prysm/v1alpha1/attestation/attestation_utils_test.go

@@ -81,6 +81,14 @@ func TestAttestingIndices(t *testing.T) {
 			},
 			want: []uint64{0, 1},
 		},
+		{
+			name: "Electra - No attester in committee",
+			args: args{
+				att:        &eth.AttestationElectra{AggregationBits: bitfield.Bitlist{0b11100}},
+				committees: [][]primitives.ValidatorIndex{{0, 1}, {0, 1}},
+			},
+			err: "no attesting indices found for committee index 0",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {