From ae8827bb6bae6412321323dc8c538c18e4bc5b29 Mon Sep 17 00:00:00 2001
From: Emmanuel T Odeke <emmanuel@orijtech.com>
Date: Mon, 22 Nov 2021 18:35:16 +0100
Subject: [PATCH] rules/sdk: add pass to reject time.Now()

time.Now() uses local clocks that unfortunately when used
in distributed consensus introduce lots of skew and
can be exploited in vulnerabilities. Instead there is
consensus aware clock whose timestamp is embedded in
the current Block. This pass rejects usages as per
https://forum.cosmos.network/t/cosmos-sdk-vulnerability-retrospective-security-advisory-jackfruit-october-12-2021/5349

Updates #1
---
 rules/rulelist.go     |  1 +
 rules/rules_test.go   |  4 +++
 rules/sdk/time_now.go | 84 +++++++++++++++++++++++++++++++++++++++++++
 testutils/source.go   | 19 ++++++++++
 4 files changed, 108 insertions(+)
 create mode 100644 rules/sdk/time_now.go

diff --git a/rules/rulelist.go b/rules/rulelist.go
index 6783957..df2870a 100644
--- a/rules/rulelist.go
+++ b/rules/rulelist.go
@@ -117,6 +117,7 @@ func Generate(filters ...RuleFilter) RuleList {
 		{"G703", "Errors that don't result in rollback", sdk.NewErrorNotPropagated},
 		{"G704", "Strconv invalid bitSize and cast", sdk.NewStrconvIntBitSizeOverflow},
 		{"G705", "Iterating over maps undeterministically", sdk.NewMapRangingCheck},
+		{"G706", "Non-consensus aware time.Now() usage", sdk.NewTimeNowRefusal},
 	}
 
 	ruleMap := make(map[string]RuleDefinition)
diff --git a/rules/rules_test.go b/rules/rules_test.go
index 0b3754e..0acf234 100644
--- a/rules/rules_test.go
+++ b/rules/rules_test.go
@@ -95,6 +95,10 @@ var _ = Describe("gosec rules", func() {
 			runner("G705", testutils.SampleCodeMapRangingNonDeterministic)
 		})
 
+		It("should detect non-consensus aware time.Now() usage", func() {
+			runner("G706", testutils.SampleCodeTimeNowNonCensusAware)
+		})
+
 		It("should detect DoS vulnerability via decompression bomb", func() {
 			runner("G110", testutils.SampleCodeG110)
 		})
diff --git a/rules/sdk/time_now.go b/rules/sdk/time_now.go
new file mode 100644
index 0000000..c174ea7
--- /dev/null
+++ b/rules/sdk/time_now.go
@@ -0,0 +1,84 @@
+// (c) Copyright 2021 Hewlett Packard Enterprise Development LP
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sdk
+
+import (
+	"errors"
+	"go/ast"
+
+	"github.com/securego/gosec/v2"
+)
+
+// This static analyzer discourages the use of time.Now() as it was discovered that
+// its usage caused local non-determinism as reported and detailed at
+// https://forum.cosmos.network/t/cosmos-sdk-vulnerability-retrospective-security-advisory-jackfruit-october-12-2021/5349
+
+type timeNowCheck struct {
+	gosec.MetaData
+	calls gosec.CallList
+}
+
+func (tmc *timeNowCheck) ID() string { return tmc.MetaData.ID }
+
+func (tmc *timeNowCheck) Match(node ast.Node, ctx *gosec.Context) (*gosec.Issue, error) {
+	// We want to catch all function invocations as well as assignments of any of the form:
+	// .Value = time.Now().*
+	// fn := time.Now
+	callExpr, ok := node.(*ast.CallExpr)
+	if !ok {
+		return nil, nil
+	}
+
+	sel, ok := callExpr.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return nil, nil
+	}
+
+	if sel.Sel.Name != "Now" {
+		return nil, nil
+	}
+
+	switch x := sel.X.(type) {
+	case *ast.Ident:
+		if x.Name != "time" {
+			return nil, nil
+		}
+
+	case *ast.SelectorExpr:
+		if x.Sel.Name != "time" {
+			return nil, nil
+		}
+	}
+
+	// By this point issue the error.
+	return nil, errors.New("time.Now() is non-deterministic for distributed consensus, you should use the current Block's timestamp")
+}
+
+func NewTimeNowRefusal(id string, config gosec.Config) (rule gosec.Rule, nodes []ast.Node) {
+	calls := gosec.NewCallList()
+
+	tnc := &timeNowCheck{
+		MetaData: gosec.MetaData{
+			ID:         id,
+			Severity:   gosec.High,
+			Confidence: gosec.High,
+			What:       "Non-determinism from using non-consensus aware time.Now()",
+		},
+		calls: calls,
+	}
+
+	nodes = append(nodes, (*ast.CallExpr)(nil))
+	return tnc, nodes
+}
diff --git a/testutils/source.go b/testutils/source.go
index e61a609..d1e139b 100644
--- a/testutils/source.go
+++ b/testutils/source.go
@@ -2528,4 +2528,23 @@ func noop(keys []string) []string {return keys}
 `}, 13, gosec.NewConfig(),
 		},
 	}
+
+	SampleCodeTimeNowNonCensusAware = []CodeSample{
+		{
+			[]string{`
+package main
+
+func main() {
+        _ = time.Now()
+}`}, 3, gosec.NewConfig(),
+		},
+		{
+			[]string{`
+package main
+
+func main() {
+        _ = time.Now().Unix()
+}`}, 3, gosec.NewConfig(),
+		},
+	}
 )