Validate ingress path fields (#9309)

* Validate characters in path fields

* Add e2e tests for path validation

* Fix review comments

pkg/util/ingress/ingress.go

@@ -18,15 +18,30 @@ package ingress
 
 import (
 	"fmt"
+	"regexp"
 	"strings"
 
+	networkingv1 "k8s.io/api/networking/v1"
 	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/ingress-nginx/internal/ingress/annotations/parser"
 	"k8s.io/ingress-nginx/internal/k8s"
 	"k8s.io/ingress-nginx/internal/net/ssl"
 	"k8s.io/ingress-nginx/pkg/apis/ingress"
 	"k8s.io/klog/v2"
 )
 
+const (
+	alphaNumericChars = `\-\.\_\~a-zA-Z0-9/`
+	regexEnabledChars = `\^\$\[\]\(\)\{\}\*\+`
+)
+
+var (
+	// pathAlphaNumeric is a regex validation of something like "^/[a-zA-Z]+$" on path
+	pathAlphaNumeric = regexp.MustCompile("^/[" + alphaNumericChars + "]*$").MatchString
+	// pathRegexEnabled is a regex validation of paths that may contain regex.
+	pathRegexEnabled = regexp.MustCompile("^/[" + alphaNumericChars + regexEnabledChars + "]*$").MatchString
+)
+
 func GetRemovedHosts(rucfg, newcfg *ingress.Configuration) []string {
 	oldSet := sets.NewString()
 	newSet := sets.NewString()
@@ -231,3 +246,13 @@ func BuildRedirects(servers []*ingress.Server) []*redirect {
 
 	return redirectServers
 }
+
+// IsSafePath verifies if the path used in ingress object contains only valid characters.
+// It will behave differently if regex is enabled or not
+func IsSafePath(copyIng *networkingv1.Ingress, path string) bool {
+	isRegex, _ := parser.GetBoolAnnotation("use-regex", copyIng)
+	if isRegex {
+		return pathRegexEnabled(path)
+	}
+	return pathAlphaNumeric(path)
+}