store/internal: validate keys before calling ProofsFromMap (#9235)

Otherwise, an empty key as input or present in data can cause a panic at
runtime.

Caught by oss-fuzz: https://oss-fuzz.com/testcase-detail/4647668077953024

Fixes #9233

store/internal/proofs/create.go

@@ -1,6 +1,7 @@
 package proofs
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 
@@ -9,6 +10,11 @@ import (
 	sdkmaps "github.com/cosmos/cosmos-sdk/store/internal/maps"
 )
 
+var (
+	ErrEmptyKey       = errors.New("key is empty")
+	ErrEmptyKeyInData = errors.New("data contains empty key")
+)
+
 // TendermintSpec constrains the format from ics23-tendermint (crypto/merkle SimpleProof)
 var TendermintSpec = &ics23.ProofSpec{
 	LeafSpec: &ics23.LeafOp{
@@ -31,6 +37,9 @@ CreateMembershipProof will produce a CommitmentProof that the given key (and que
 If the key doesn't exist in the tree, this will return an error.
 */
 func CreateMembershipProof(data map[string][]byte, key []byte) (*ics23.CommitmentProof, error) {
+	if len(key) == 0 {
+		return nil, ErrEmptyKey
+	}
 	exist, err := createExistenceProof(data, key)
 	if err != nil {
 		return nil, err
@@ -48,6 +57,9 @@ CreateNonMembershipProof will produce a CommitmentProof that the given key doesn
 If the key exists in the tree, this will return an error.
 */
 func CreateNonMembershipProof(data map[string][]byte, key []byte) (*ics23.CommitmentProof, error) {
+	if len(key) == 0 {
+		return nil, ErrEmptyKey
+	}
 	// ensure this key is not in the store
 	if _, ok := data[string(key)]; ok {
 		return nil, fmt.Errorf("cannot create non-membership proof if key is in map")
@@ -89,6 +101,11 @@ func CreateNonMembershipProof(data map[string][]byte, key []byte) (*ics23.Commit
 }
 
 func createExistenceProof(data map[string][]byte, key []byte) (*ics23.ExistenceProof, error) {
+	for k := range data {
+		if k == "" {
+			return nil, ErrEmptyKeyInData
+		}
+	}
 	value, ok := data[string(key)]
 	if !ok {
 		return nil, fmt.Errorf("cannot make existence proof if key is not in map")

store/internal/proofs/create_test.go

@@ -1,9 +1,11 @@
 package proofs
 
 import (
+	"errors"
 	"testing"
 
 	ics23 "github.com/confio/ics23/go"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestCreateMembership(t *testing.T) {
@@ -87,3 +89,24 @@ func TestCreateNonMembership(t *testing.T) {
 		})
 	}
 }
+
+func TestInvalidKey(t *testing.T) {
+	tests := []struct {
+		name string
+		f    func(data map[string][]byte, key []byte) (*ics23.CommitmentProof, error)
+		data map[string][]byte
+		key  []byte
+		err  error
+	}{
+		{"CreateMembershipProof empty key", CreateMembershipProof, map[string][]byte{"": nil}, []byte(""), ErrEmptyKey},
+		{"CreateMembershipProof empty key in data", CreateMembershipProof, map[string][]byte{"": nil, " ": nil}, []byte(" "), ErrEmptyKeyInData},
+		{"CreateNonMembershipProof empty key", CreateNonMembershipProof, map[string][]byte{" ": nil}, []byte(""), ErrEmptyKey},
+		{"CreateNonMembershipProof empty key in data", CreateNonMembershipProof, map[string][]byte{"": nil}, []byte(" "), ErrEmptyKeyInData},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := tc.f(tc.data, tc.key)
+			assert.True(t, errors.Is(err, tc.err))
+		})
+	}
+}