From c53af75658009c2ab8fabb6602d2a269f53e8339 Mon Sep 17 00:00:00 2001
From: Cedric Staub <css@css.bio>
Date: Wed, 27 Jul 2016 21:37:57 -0700
Subject: [PATCH] Detect use of rand.Read from math/rand

---
 rulelist.go        |  1 +
 rules/rand.go      | 55 ++++++++++++++++++++++++++++++++++++++++++++++
 rules/rand_test.go | 55 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 rules/rand.go
 create mode 100644 rules/rand_test.go

diff --git a/rulelist.go b/rulelist.go
index c51bdba..8e4718b 100644
--- a/rulelist.go
+++ b/rulelist.go
@@ -53,6 +53,7 @@ func newRulelist() rulelist {
 	rs.register("exec", rules.NewSubproc)
 	rs.register("errors", rules.NewNoErrorCheck)
 	rs.register("httpoxy", rules.NewHttpoxyTest)
+	rs.register("rand", rules.NewWeakRandCheck)
 	return rs
 }
 
diff --git a/rules/rand.go b/rules/rand.go
new file mode 100644
index 0000000..eff2204
--- /dev/null
+++ b/rules/rand.go
@@ -0,0 +1,55 @@
+// (c) Copyright 2016 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 rules
+
+import (
+	"go/ast"
+	"regexp"
+
+	gas "github.com/HewlettPackard/gas/core"
+)
+
+type WeakRand struct {
+	gas.MetaData
+	pattern     *regexp.Regexp
+	packageName string
+	packagePath string
+}
+
+func (w *WeakRand) Match(n ast.Node, c *gas.Context) (*gas.Issue, error) {
+	if call := gas.MatchCall(n, w.pattern); call != nil {
+		for _, pkg := range c.Pkg.Imports() {
+			if pkg.Name() == w.packageName && pkg.Path() == w.packagePath {
+				return gas.NewIssue(c, n, w.What, w.Severity, w.Confidence), nil
+			}
+		}
+	}
+	return nil, nil
+}
+
+func NewWeakRandCheck() (r gas.Rule, n ast.Node) {
+	r = &WeakRand{
+		pattern:     regexp.MustCompile(`^rand.Read$`),
+		packageName: "rand",
+		packagePath: "math/rand",
+		MetaData: gas.MetaData{
+			Severity:   gas.High,
+			Confidence: gas.Medium,
+			What:       "Use of weak random number generator (math/rand instead of crypto/rand)",
+		},
+	}
+	n = (*ast.CallExpr)(nil)
+	return
+}
diff --git a/rules/rand_test.go b/rules/rand_test.go
new file mode 100644
index 0000000..a65a723
--- /dev/null
+++ b/rules/rand_test.go
@@ -0,0 +1,55 @@
+// (c) Copyright 2016 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 rules
+
+import (
+	"testing"
+
+	gas "github.com/HewlettPackard/gas/core"
+)
+
+func TestRandOk(t *testing.T) {
+	analyzer := gas.NewAnalyzer(false, nil)
+	analyzer.AddRule(NewWeakRandCheck())
+
+	issues := gasTestRunner(
+		`
+		package samples
+
+		import "crypto/rand"
+
+		func main() {
+			good, err := rand.Read(nil)
+		}`, analyzer)
+
+	checkTestResults(t, issues, 0, "Not expected to match")
+}
+
+func TestRandBad(t *testing.T) {
+	analyzer := gas.NewAnalyzer(false, nil)
+	analyzer.AddRule(NewWeakRandCheck())
+
+	issues := gasTestRunner(
+		`
+		package samples
+
+		import "math/rand"
+
+		func main() {
+			bad, err := rand.Read(nil)
+		}`, analyzer)
+
+	checkTestResults(t, issues, 1, "Use of weak random number generator (math/rand instead of crypto/rand)")
+}