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

Author: odeke-em

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)

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)
 		})

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/cosmos/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
+}

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(),
+		},
+	}
 )