Add a rule which detects when there is potential integer overflow (#422)

* Add G109(Potential Integer OverFlow Detection)

Signed-off-by: Hiroki Suezawa <suezawa@gmail.com>

* add CWE to G109(Potential Integer Overflow)

Signed-off-by: Hiroki Suezawa <suezawa@gmail.com>

* Modify G109 to use gosec.Context

Signed-off-by: Hiroki Suezawa <suezawa@gmail.com>

rules/integer_overflow.go

@@ -0,0 +1,91 @@
+// (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 (
+	"fmt"
+	"github.com/securego/gosec"
+	"go/ast"
+)
+
+type integerOverflowCheck struct {
+	gosec.MetaData
+	calls gosec.CallList
+}
+
+func (i *integerOverflowCheck) ID() string {
+	return i.MetaData.ID
+}
+
+func (i *integerOverflowCheck) Match(node ast.Node, ctx *gosec.Context) (*gosec.Issue, error) {
+	var atoiVarName map[string]ast.Node
+
+	// To check multiple lines, ctx.PassedValues is used to store temporary data.
+	if _, ok := ctx.PassedValues[i.ID()]; !ok {
+		atoiVarName = make(map[string]ast.Node)
+		ctx.PassedValues[i.ID()] = atoiVarName
+	} else if pv, ok := ctx.PassedValues[i.ID()].(map[string]ast.Node); ok {
+		atoiVarName = pv
+	} else {
+		return nil, fmt.Errorf("PassedValues[%s] of Context is not map[string]ast.Node, but %T", i.ID(), ctx.PassedValues[i.ID()])
+	}
+
+	// strconv.Atoi is a common function.
+	// To reduce false positives, This rule detects code which is converted to int32/int16 only.
+	switch n := node.(type) {
+	case *ast.FuncDecl:
+		// Clear atoiVarName by function
+		ctx.PassedValues[i.ID()] = make(map[string]ast.Node)
+	case *ast.AssignStmt:
+		for _, expr := range n.Rhs {
+			if callExpr, ok := expr.(*ast.CallExpr); ok && i.calls.ContainsCallExpr(callExpr, ctx, false) != nil {
+				if idt, ok := n.Lhs[0].(*ast.Ident); ok && idt.Name != "_" {
+					// Example:
+					//  v, _ := strconv.Atoi("1111")
+					// Add "v" to atoiVarName map
+					atoiVarName[idt.Name] = n
+				}
+			}
+		}
+	case *ast.CallExpr:
+		if fun, ok := n.Fun.(*ast.Ident); ok {
+			if fun.Name == "int32" || fun.Name == "int16" {
+				if idt, ok := n.Args[0].(*ast.Ident); ok {
+					if n, ok := atoiVarName[idt.Name]; ok {
+						// Detect int32(v) and int16(v)
+						return gosec.NewIssue(ctx, n, i.ID(), i.What, i.Severity, i.Confidence), nil
+					}
+				}
+			}
+		}
+	}
+
+	return nil, nil
+}
+
+// NewIntegerOverflowCheck detects if there is potential Integer OverFlow
+func NewIntegerOverflowCheck(id string, conf gosec.Config) (gosec.Rule, []ast.Node) {
+	calls := gosec.NewCallList()
+	calls.Add("strconv", "Atoi")
+	return &integerOverflowCheck{
+		MetaData: gosec.MetaData{
+			ID:         id,
+			Severity:   gosec.High,
+			Confidence: gosec.Medium,
+			What:       "Potential Integer overflow made by strconv.Atoi result conversion to int16/32",
+		},
+		calls: calls,
+	}, []ast.Node{(*ast.FuncDecl)(nil), (*ast.AssignStmt)(nil), (*ast.CallExpr)(nil)}
+}