blob: CommitmentProof.Verify should firstly check that root is non-empty before doing all the validation work then crashing

[odeke-em]

Celestia Node version

1a1286f

Steps to reproduce it

If we run this code repro

package blob_test

import (
        "testing"

        "github.com/celestiaorg/celestia-app/v2/pkg/proof"
        "github.com/celestiaorg/celestia-node/blob" 
)       
        
func TestCommitmentProofRowProofVerify(t *testing.T) {
        cp := &blob.CommitmentProof{
                RowProof: proof.RowProof{
                        Proofs: []*proof.Proof{{}},
                },
        }       
        _, _ = cp.Verify(nil, 1)
}

Expected result

An error and not a panic

Actual result

$ go test -run=TestCommitmentProofRowProofVerify
# github.com/celestiaorg/celestia-node/blob.test
--- FAIL: TestCommitmentProofRowProofVerify (0.00s)
panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 9 [running]:
testing.tRunner.func1.2({0x1069be820, 0xc000064c78})
	/Users/emmanuelodeke/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.0.darwin-amd64/src/testing/testing.go:1632 +0x230
testing.tRunner.func1()
	/Users/emmanuelodeke/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.0.darwin-amd64/src/testing/testing.go:1635 +0x35e
panic({0x1069be820?, 0xc000064c78?})
	/Users/emmanuelodeke/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.0.darwin-amd64/src/runtime/panic.go:785 +0x132
github.com/celestiaorg/celestia-app/v2/pkg/proof.RowProof.VerifyProof({{0x0, 0x0, 0x0}, {0xc0010a7f58, 0x1, 0x1}, {0x0, 0x0, 0x0}, 0x0, ...}, ...)
	/Users/emmanuelodeke/go/pkg/mod/github.com/celestiaorg/celestia-app/v2@v2.1.2/pkg/proof/row_proof.go:32 +0x172
github.com/celestiaorg/celestia-node/blob.(*CommitmentProof).Verify(0xc0010a7eb8, {0x0, 0x0, 0x0}, 0x1)
	/Users/emmanuelodeke/go/src/github.com/celestiaorg/celestia-node/blob/commitment_proof.go:146 +0x779
github.com/celestiaorg/celestia-node/blob_test.TestCommitmentProofRowProofVerify(0xc000637860?)
	/Users/emmanuelodeke/go/src/github.com/celestiaorg/celestia-node/blob/repro_test.go:18 +0x94
testing.tRunner(0xc000637860, 0x106b030e0)
	/Users/emmanuelodeke/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.0.darwin-amd64/src/testing/testing.go:1690 +0xf4
created by testing.(*T).Run in goroutine 1
	/Users/emmanuelodeke/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.23.0.darwin-amd64/src/testing/testing.go:1743 +0x390
exit status 2
FAIL	github.com/celestiaorg/celestia-node/blob	1.583s

Relevant log output

## Suggested fix

diff --git a/blob/commitment_proof.go b/blob/commitment_proof.go
index 8fa74671..f6af47a9 100644
--- a/blob/commitment_proof.go
+++ b/blob/commitment_proof.go
@@ -2,6 +2,7 @@ package blob
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 
 	"github.com/celestiaorg/celestia-app/v2/pkg/appconsts"
@@ -85,6 +86,10 @@ func (commitmentProof *CommitmentProof) Validate() error {
 // Expects the commitment proof to be properly formulated and validated
 // using the Validate() function.
 func (commitmentProof *CommitmentProof) Verify(root []byte, subtreeRootThreshold int) (bool, error) {
+	if len(root) == 0 {
+		return false, errors.New("root must be non-empty")
+	}
+
 	nmtHasher := nmt.NewNmtHasher(appconsts.NewBaseHashFunc(), share.NamespaceSize, true)
 
 	// computes the total number of shares proven.
@@ -93,6 +98,10 @@ func (commitmentProof *CommitmentProof) Verify(root []byte, subtreeRootThreshold
 		numberOfShares += proof.End() - proof.Start()
 	}

cc @liamsi @musalbas @rootulp