From 004f51a311edab4b8971a85afdf3429919424043 Mon Sep 17 00:00:00 2001
From: Federico Kunze <31522760+fedekunze@users.noreply.github.com>
Date: Fri, 29 Jan 2021 23:48:26 -0300
Subject: [PATCH] backport #8479

---
 CHANGELOG.md                  |  6 ++++
 x/bank/types/metadata.go      | 39 +++++++++++++++++++++++--
 x/bank/types/metadata_test.go | 55 ++++++++++++++++++++++++++++++++++-
 3 files changed, 97 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 973ea6e054ce..f9190ec3d8d7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,12 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 # Changelog
 
+## Unreleased
+
+### Improvements
+
+* (x/bank) [\#8479](https://github.com/cosmos/cosmos-sdk/pull/8479) Aditional client denom metadata validation for `base` and `display` denoms.
+
 ## [v0.41.0](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.41.0) - 2021-01-26
 
 ### State Machine Breaking
diff --git a/x/bank/types/metadata.go b/x/bank/types/metadata.go
index 5106964e994e..ce7794053d93 100644
--- a/x/bank/types/metadata.go
+++ b/x/bank/types/metadata.go
@@ -1,13 +1,19 @@
 package types
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
-// Validate performs a basic validation of the coin metadata fields
+// Validate performs a basic validation of the coin metadata fields. It checks:
+//  - Base and Display denominations are valid coin denominations
+//  - Base and Display denominations are present in the DenomUnit slice
+//  - Base denomination has exponent 0
+//  - Denomination units are sorted in ascending order
+//  - Denomination units not duplicated
 func (m Metadata) Validate() error {
 	if err := sdk.ValidateDenom(m.Base); err != nil {
 		return fmt.Errorf("invalid metadata base denom: %w", err)
@@ -17,12 +23,37 @@ func (m Metadata) Validate() error {
 		return fmt.Errorf("invalid metadata display denom: %w", err)
 	}
 
+	var (
+		hasDisplay      bool
+		currentExponent uint32 // check that the exponents are increasing
+	)
+
 	seenUnits := make(map[string]bool)
-	for _, denomUnit := range m.DenomUnits {
+
+	for i, denomUnit := range m.DenomUnits {
+		// The first denomination unit MUST be the base
+		if i == 0 {
+			// validate denomination and exponent
+			if denomUnit.Denom != m.Base {
+				return fmt.Errorf("metadata's first denomination unit must be the one with base denom '%s'", m.Base)
+			}
+			if denomUnit.Exponent != 0 {
+				return fmt.Errorf("the exponent for base denomination unit %s must be 0", m.Base)
+			}
+		} else if currentExponent >= denomUnit.Exponent {
+			return errors.New("denom units should be sorted asc by exponent")
+		}
+
+		currentExponent = denomUnit.Exponent
+
 		if seenUnits[denomUnit.Denom] {
 			return fmt.Errorf("duplicate denomination unit %s", denomUnit.Denom)
 		}
 
+		if denomUnit.Denom == m.Display {
+			hasDisplay = true
+		}
+
 		if err := denomUnit.Validate(); err != nil {
 			return err
 		}
@@ -30,6 +61,10 @@ func (m Metadata) Validate() error {
 		seenUnits[denomUnit.Denom] = true
 	}
 
+	if !hasDisplay {
+		return fmt.Errorf("metadata must contain a denomination unit with display denom '%s'", m.Display)
+	}
+
 	return nil
 }
 
diff --git a/x/bank/types/metadata_test.go b/x/bank/types/metadata_test.go
index 29f4d220f95f..64241e6098e0 100644
--- a/x/bank/types/metadata_test.go
+++ b/x/bank/types/metadata_test.go
@@ -51,7 +51,7 @@ func TestMetadataValidate(t *testing.T) {
 				Description: "The native staking token of the Cosmos Hub.",
 				DenomUnits: []*types.DenomUnit{
 					{"uatom", uint32(0), []string{"microatom"}},
-					{"uatom", uint32(0), []string{"microatom"}},
+					{"uatom", uint32(1), []string{"microatom"}},
 				},
 				Base:    "uatom",
 				Display: "atom",
@@ -94,6 +94,59 @@ func TestMetadataValidate(t *testing.T) {
 			},
 			true,
 		},
+		{
+			"no base denom unit",
+			types.Metadata{
+				Description: "The native staking token of the Cosmos Hub.",
+				DenomUnits: []*types.DenomUnit{
+					{"matom", uint32(3), []string{"milliatom"}},
+					{"atom", uint32(6), nil},
+				},
+				Base:    "uatom",
+				Display: "atom",
+			},
+			true,
+		},
+		{
+			"base denom exponent not zero",
+			types.Metadata{
+				Description: "The native staking token of the Cosmos Hub.",
+				DenomUnits: []*types.DenomUnit{
+					{"uatom", uint32(1), []string{"microatom"}},
+					{"matom", uint32(3), []string{"milliatom"}},
+					{"atom", uint32(6), nil},
+				},
+				Base:    "uatom",
+				Display: "atom",
+			},
+			true,
+		},
+		{
+			"no display denom unit",
+			types.Metadata{
+				Description: "The native staking token of the Cosmos Hub.",
+				DenomUnits: []*types.DenomUnit{
+					{"uatom", uint32(0), []string{"microatom"}},
+				},
+				Base:    "uatom",
+				Display: "atom",
+			},
+			true,
+		},
+		{
+			"denom units not sorted",
+			types.Metadata{
+				Description: "The native staking token of the Cosmos Hub.",
+				DenomUnits: []*types.DenomUnit{
+					{"uatom", uint32(0), []string{"microatom"}},
+					{"atom", uint32(6), nil},
+					{"matom", uint32(3), []string{"milliatom"}},
+				},
+				Base:    "uatom",
+				Display: "atom",
+			},
+			true,
+		},
 	}
 
 	for _, tc := range testCases {