fix(x/feegrant): prevent duplicate grants in genesis state (#24134)

Co-authored-by: Alex | Interchain Labs <alex@interchainlabs.io>

x/feegrant/CHANGELOG.md

@@ -25,6 +25,10 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ## [Unreleased]
 
+### Bug Fixes
+
+* [#24134](https://github.com/cosmos/cosmos-sdk/pull/24134) Add validation to prevent duplicate fee grants in genesis state.
+
 ## [v0.2.0](https://github.com/cosmos/cosmos-sdk/releases/tag/x/feegrant/v0.2.0) - 2025-04-24
 
 * SDK v0.53.x support.

x/feegrant/genesis.go

@@ -1,6 +1,8 @@
 package feegrant
 
 import (
+	"fmt"
+
 	"github.com/cosmos/cosmos-sdk/codec/types"
 )
 
@@ -15,7 +17,17 @@ func NewGenesisState(entries []Grant) *GenesisState {
 
 // ValidateGenesis ensures all grants in the genesis state are valid
 func ValidateGenesis(data GenesisState) error {
+	// Check for duplicate grants by (granter, grantee) pair
+	seen := make(map[string]struct{})
+
 	for _, f := range data.Allowances {
+		// Create a unique key for (granter, grantee) pair using a delimiter
+		key := fmt.Sprintf("%s|%s", f.Granter, f.Grantee)
+		if _, exists := seen[key]; exists {
+			return fmt.Errorf("duplicate feegrant found from granter %q to grantee %q", f.Granter, f.Grantee)
+		}
+		seen[key] = struct{}{}
+
 		grant, err := f.GetGrant()
 		if err != nil {
 			return err

x/feegrant/genesis_test.go

@@ -0,0 +1,46 @@
+package feegrant
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+
+	"cosmossdk.io/math"
+
+	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+func TestDuplicateGrantsInGenesis(t *testing.T) {
+	// Create dummy addresses for test
+	granter := sdk.AccAddress("granter_address____").String()
+	grantee := sdk.AccAddress("grantee_address____").String()
+
+	// Create a BasicAllowance for testing
+	allowance := &BasicAllowance{
+		SpendLimit: sdk.NewCoins(sdk.NewCoin("foo", math.NewInt(100))),
+	}
+
+	any, err := codectypes.NewAnyWithValue(allowance)
+	assert.NilError(t, err)
+
+	// Create Genesis state with duplicate allowances
+	genesisState := &GenesisState{
+		Allowances: []Grant{
+			{
+				Granter:   granter,
+				Grantee:   grantee,
+				Allowance: any,
+			},
+			{
+				Granter:   granter,
+				Grantee:   grantee,
+				Allowance: any,
+			},
+		},
+	}
+
+	// Validation should fail with duplicate feegrant error
+	err = ValidateGenesis(*genesisState)
+	assert.ErrorContains(t, err, "duplicate feegrant found")
+}