Add a new rule to detect integer overflow on integer types conversion

Signed-off-by: Cosmin Cojocar <cosmin@cojocar.ch>

analyzers/conversion_overflow.go

@@ -0,0 +1,134 @@
+// (c) Copyright gosec's authors
+//
+// 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 analyzers
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+
+	"github.com/securego/gosec/v2/issue"
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/buildssa"
+	"golang.org/x/tools/go/ssa"
+)
+
+func newConversionOverflowAnalyzer(id string, description string) *analysis.Analyzer {
+	return &analysis.Analyzer{
+		Name:     id,
+		Doc:      description,
+		Run:      runConversionOverflow,
+		Requires: []*analysis.Analyzer{buildssa.Analyzer},
+	}
+}
+
+func runConversionOverflow(pass *analysis.Pass) (interface{}, error) {
+	ssaResult, err := getSSAResult(pass)
+	if err != nil {
+		return nil, fmt.Errorf("building ssa representation: %w", err)
+	}
+
+	issues := []*issue.Issue{}
+	for _, mcall := range ssaResult.SSA.SrcFuncs {
+		for _, block := range mcall.DomPreorder() {
+			for _, instr := range block.Instrs {
+				switch instr := instr.(type) {
+				case *ssa.Convert:
+					src := instr.X.Type().String()
+					dst := instr.Type().String()
+					if isIntOverflow(src, dst) {
+						issue := newIssue(pass.Analyzer.Name,
+							fmt.Sprintf("integer overflow conversion %s -> %s", src, dst),
+							pass.Fset,
+							instr.Pos(),
+							issue.High,
+							issue.Medium,
+						)
+						issues = append(issues, issue)
+					}
+				}
+			}
+		}
+	}
+
+	if len(issues) > 0 {
+		return issues, nil
+	}
+	return nil, nil
+}
+
+type integer struct {
+	signed bool
+	size   int
+}
+
+func parseIntType(intType string) (integer, error) {
+	re := regexp.MustCompile(`(?P<type>u?int)(?P<size>\d{2})?`)
+	matches := re.FindStringSubmatch(intType)
+	if matches == nil {
+		return integer{}, fmt.Errorf("no integer type match found for %s", intType)
+	}
+
+	it := matches[re.SubexpIndex("type")]
+	is := matches[re.SubexpIndex("size")]
+
+	signed := false
+	if it == "int" {
+		signed = true
+	}
+
+	// use default system int type in case size is not present in the type
+	intSize := strconv.IntSize
+	if is != "" {
+		var err error
+		intSize, err = strconv.Atoi(is)
+		if err != nil {
+			return integer{}, fmt.Errorf("failed to parse the integer type size: %w", err)
+		}
+	}
+
+	return integer{signed: signed, size: intSize}, nil
+}
+
+func isIntOverflow(src string, dst string) bool {
+	srcInt, err := parseIntType(src)
+	if err != nil {
+		return false
+	}
+
+	dstInt, err := parseIntType(dst)
+	if err != nil {
+		return false
+	}
+
+	// converting uint to int of the same size or smaller might lead to overflow
+	if !srcInt.signed && dstInt.signed && dstInt.size <= srcInt.size {
+		return true
+	}
+	// converting uint to unit of a smaller size might lead to overflow
+	if !srcInt.signed && !dstInt.signed && dstInt.size < srcInt.size {
+		return true
+	}
+	// converting int to int of a smaller size might lead to overflow
+	if srcInt.signed && dstInt.signed && dstInt.size < srcInt.size {
+		return true
+	}
+	// converting int to uint of a smaller size might lead to overflow
+	if srcInt.signed && !dstInt.signed && dstInt.size < srcInt.size && srcInt.size-dstInt.size > 8 {
+		return true
+	}
+
+	return false
+}