Add a fuzzing feature for various SecurityContexts in a pod's manifest (#11)

It uses google/gofuzz to generate a random but somehow valid
SecurityContext that can be injected into a pod's manifest. It can
generate a pod securityContext, a container securityContext and an
initContainer securityContext.

Author: mtardy

.github/workflows/golangci-lint.yaml

@@ -24,5 +24,3 @@ jobs:
           version: v1.49.0
           # Optional: show only new issues if it's a pull request. The default value is `false`.
           only-new-issues: true
-          args: --timeout=5m
-

.golangci.yaml

@@ -1,5 +1,6 @@
 run:
   go: '1.19'
+  timeout: 5m
 
 linters:
   disable-all: true

README.md

@@ -27,6 +27,9 @@ pentesting process.
     * [With Nix](#with-nix)
     * [Via Go](#via-go)
 * [Usage](#usage)
+    * [Digging](#digging)
+    * [Generating](#generating)
+    * [Fuzzing](#fuzzing)
 * [Details](#details)
     * [Updates](#updates)
     * [Usage warning](#usage-warning)
@@ -115,6 +118,8 @@ go install github.com/quarkslab/kdigger@main
 
 ## Usage
 
+### Digging
+
 What you generally want to do is running all the buckets with `dig all` or just
 `d a`:
 ```bash
@@ -180,6 +185,8 @@ Global Flags:
   -w, --width int       Width for the human output (default 140)
 ```
 
+### Generating
+
 You can also generate useful templates for pods with security features disabled
 to escalate privileges when you can create such a pod. See the help for this
 specific command for more information.
@@ -202,6 +209,9 @@ boolean flags to disabled security features. Examples:
   # Create a custom privileged pod
   kdigger gen --privileged --image bash --command watch --command date | kubectl apply -f -
 
+  # Fuzz the API server admission
+  kdigger gen --fuzz-pod --fuzz-init --fuzz-container | kubectl apply --dry-run=server -f -
+
 Usage:
   kdigger gen [name] [flags]
 
@@ -211,11 +221,15 @@ Aliases:
 Flags:
       --all                   Enable everything
       --command stringArray   Container command used (default [sleep,infinitely])
+      --fuzz-container        Generate a random container security context. (will override other options)
+      --fuzz-init             Generate a random init container security context.
+      --fuzz-pod              Generate a random pod security context.
   -h, --help                  help for gen
       --hostnetwork           Add the hostNetwork flag on the whole pod
       --hostpath              Add a hostPath volume to the container
       --hostpid               Add the hostPid flag on the whole pod
       --image string          Container image used (default "busybox")
+  -n, --namespace string      Kubernetes namespace to use
       --privileged            Add the security flag to the security context of the pod
       --tolerations           Add tolerations to be schedulable on most nodes
 
@@ -224,6 +238,28 @@ Global Flags:
   -w, --width int       Width for the human output (default 140)
 ```
 
+### Fuzzing
+
+You can try to fuzz your API admission with `kdigger`, find
+[some information in this PR](https://github.com/quarkslab/kdigger/pull/11).
+It can be interesting to see if your sets of custom policies are resistant
+against randomly generated pod manifest.
+
+See how `kdigger` can generate random container securityContext:
+```console
+./kdigger gen --fuzz-container -o json | jq '.spec.containers[].securityContext'
+```
+
+Or generate a dozen:
+```bash
+for _ in {1..12}; do ./kdigger gen --fuzz-container -o json | jq '.spec.containers[].securityContext'; done
+```
+
+Fuzz your admission API with simple commands similar to:
+```bash
+while true; do ./kdigger gen --fuzz-pod --fuzz-init --fuzz-container | kubectl apply --dry-run=server -f -; done
+```
+
 ## Details
 
 ### Updates

commands/gen.go

@@ -12,6 +12,12 @@ var opts kgen.GenerateOpts
 
 var genAll bool
 
+var (
+	fuzzPod       bool
+	fuzzContainer bool
+	fuzzInit      bool
+)
+
 var genCmd = &cobra.Command{
 	Use:     "gen [name] [flags]",
 	Aliases: []string{"generate"},
@@ -30,7 +36,10 @@ boolean flags to disabled security features. Examples:
   kdigger gen -all mypod | kubectl apply -f -
   
   # Create a custom privileged pod
-  kdigger gen --privileged --image bash --command watch --command date | kubectl apply -f -`,
+  kdigger gen --privileged --image bash --command watch --command date | kubectl apply -f -
+
+  # Fuzz the API server admission
+  kdigger gen --fuzz-pod --fuzz-init --fuzz-container | kubectl apply --dry-run=server -f -`,
 	RunE: func(cmd *cobra.Command, args []string) error {
 		// all puts all the boolean flags to true
 		if genAll {
@@ -46,6 +55,17 @@ boolean flags to disabled security features. Examples:
 
 		pod := kgen.Generate(opts)
 
+		// optional fuzzing steps
+		if fuzzPod {
+			kgen.FuzzPodSecurityContext(&pod.Spec.SecurityContext)
+		}
+		if fuzzContainer {
+			kgen.FuzzContainerSecurityContext(&pod.Spec.Containers[0].SecurityContext)
+		}
+		if fuzzInit {
+			kgen.CopyToInitAndFuzz(&pod.Spec)
+		}
+
 		var p printers.ResourcePrinter
 		if output == outputJSON {
 			p = &printers.JSONPrinter{}
@@ -74,4 +94,8 @@ func init() {
 	genCmd.Flags().BoolVar(&opts.HostNetwork, "hostnetwork", false, "Add the hostNetwork flag on the whole pod")
 
 	genCmd.Flags().BoolVar(&genAll, "all", false, "Enable everything")
+
+	genCmd.Flags().BoolVar(&fuzzPod, "fuzz-pod", false, "Generate a random pod security context.")
+	genCmd.Flags().BoolVar(&fuzzContainer, "fuzz-container", false, "Generate a random container security context. (will override other options)")
+	genCmd.Flags().BoolVar(&fuzzInit, "fuzz-init", false, "Generate a random init container security context.")
 }

go.mod

@@ -4,6 +4,7 @@ go 1.19
 
 require (
 	github.com/genuinetools/bpfd v0.0.1
+	github.com/google/gofuzz v1.2.0
 	github.com/jedib0t/go-pretty/v6 v6.3.9
 	github.com/mitchellh/go-ps v1.0.0
 	github.com/spf13/cobra v1.5.0
@@ -39,7 +40,6 @@ require (
 	github.com/google/btree v1.1.2 // indirect
 	github.com/google/gnostic v0.6.9 // indirect
 	github.com/google/go-cmp v0.5.9 // indirect
-	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 // indirect
 	github.com/google/uuid v1.3.0 // indirect
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 // indirect

pkg/kgen/kgen.go

@@ -1,12 +1,27 @@
 package kgen
 
 import (
+	"strings"
+
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
-
 	"k8s.io/apimachinery/pkg/util/rand"
+
+	fuzz "github.com/google/gofuzz"
+	"github.com/syndtr/gocapability/capability"
+)
+
+const (
+	// The probability of capabilities to be "ALL" will be 1/fuzzCapabilityAllOrEmptyChances.
+	fuzzCapabilityAllOrEmptyChances = 6
+	fuzzNilChances                  = .5
+	// Chances of putting zero in integers used for runAsUser, runAsGroup, etc.
+	fuzzIntZeroChances = .2
 )
 
+// Fuzzing will pick a uniform integer between 0 and fuzzCapabilityRandomMaxLen - 1 for capabilities list
+var fuzzCapabilityRandomMaxLen = len(capability.List())
+
 type GenerateOpts struct {
 	Name        string
 	Image       string
@@ -19,6 +34,123 @@ type GenerateOpts struct {
 	Tolerations bool
 }
 
+var intMutator = func(e *int64, c fuzz.Continue) {
+	if c.Float64() >= fuzzIntZeroChances {
+		*e = int64(c.Int31())
+	} else {
+		*e = 0
+	}
+}
+
+var seccompMutator = func(e *v1.SeccompProfile, c fuzz.Continue) {
+	supportedProfileValues := [...]string{"Localhost", "RuntimeDefault", "Unconfined"}
+	n := c.Intn(len(supportedProfileValues))
+
+	e.Type = v1.SeccompProfileType(supportedProfileValues[n])
+	if e.Type == v1.SeccompProfileType(supportedProfileValues[0]) {
+		// spec.securityContext.seccompProfile.localhostProfile: Required value: must be set when seccomp type is Localhost
+		s := c.RandString()
+		e.LocalhostProfile = &s
+	}
+}
+
+func FuzzPodSecurityContext(sc **v1.PodSecurityContext) {
+	f := fuzz.New().NilChance(fuzzNilChances).Funcs(
+		func(e *v1.Sysctl, c fuzz.Continue) {
+			// must have at most 253 characters and match regex ^([a-z0-9]([-_a-z0-9]*[a-z0-9])?[\./])*[a-z0-9]([-_a-z0-9]*[a-z0-9])?$
+			e.Name = sysctls[c.Intn(len(sysctls))]
+			c.Fuzz(&e.Value)
+		},
+		func(e *v1.PodFSGroupChangePolicy, c fuzz.Continue) {
+			if c.Intn(2) == 0 {
+				*e = v1.FSGroupChangeAlways
+			} else {
+				*e = v1.FSGroupChangeOnRootMismatch
+			}
+		},
+		func(e *[]v1.Sysctl, c fuzz.Continue) {
+			if c.Float64() >= fuzzNilChances {
+				uniqSysctls := map[string]v1.Sysctl{}
+				for n := c.Intn(10); len(uniqSysctls) < n; {
+					var sysctl v1.Sysctl
+					c.Fuzz(&sysctl)
+					uniqSysctls[sysctl.Name] = sysctl
+				}
+				for _, v := range uniqSysctls {
+					*e = append(*e, v)
+				}
+			} else {
+				*e = []v1.Sysctl{}
+			}
+		},
+		// let's ignore Windows for now
+		func(e *v1.WindowsSecurityContextOptions, c fuzz.Continue) {
+			*e = v1.WindowsSecurityContextOptions{}
+		},
+		// for supplementalGroups, runAsUser and runAsGroup value that must be between 0 and 2147483647, inclusive
+		intMutator,
+		seccompMutator,
+	)
+
+	securityContext := &v1.PodSecurityContext{}
+
+	f.Fuzz(securityContext)
+
+	*sc = securityContext
+}
+
+// FuzzContainerSecurityContext will override the SecurityContext with random (valid) values
+func FuzzContainerSecurityContext(sc **v1.SecurityContext) {
+	// add .NilChange(0) to disable nil pointers generation, by default is 0.2
+	f := fuzz.New().NilChance(fuzzNilChances).Funcs(
+		func(e *v1.WindowsSecurityContextOptions, c fuzz.Continue) {
+			*e = v1.WindowsSecurityContextOptions{}
+		},
+		func(e *v1.Capability, c fuzz.Continue) {
+			caps := capability.List()
+			n := c.Intn(len(caps))
+			*e = v1.Capability(strings.ToUpper(caps[n].String()))
+		},
+		func(e *[]v1.Capability, c fuzz.Continue) {
+			if r := c.Intn(fuzzCapabilityAllOrEmptyChances); r == 0 {
+				*e = []v1.Capability{"ALL"}
+			} else if r == 1 {
+				*e = []v1.Capability{}
+			} else {
+				length := c.Intn(fuzzCapabilityRandomMaxLen)
+				for i := 0; i < length; i++ {
+					var cap v1.Capability
+					c.Fuzz(&cap)
+					*e = append(*e, cap)
+				}
+			}
+		},
+		// for runAsUser and runAsGroup value that must be between 0 and 2147483647, inclusive
+		intMutator,
+		seccompMutator,
+	)
+	securityContext := &v1.SecurityContext{}
+	f.Fuzz(securityContext)
+
+	// cannot set `allowPrivilegeEscalation` to false and `privileged` to true
+	// there are more interdependences, like CAP_SYS_ADMIN imply privileged but
+	// maybe it's too rare to be interesting
+	if securityContext.AllowPrivilegeEscalation != nil && !*securityContext.AllowPrivilegeEscalation {
+		b := false
+		securityContext.Privileged = &b
+	}
+
+	*sc = securityContext
+}
+
+func CopyToInitAndFuzz(spec *v1.PodSpec) {
+	if len(spec.Containers) > 0 {
+		spec.InitContainers = append(spec.InitContainers, spec.Containers[0])
+		spec.InitContainers[0].Name += "-init"
+		FuzzContainerSecurityContext(&spec.InitContainers[0].SecurityContext)
+	}
+}
+
 func Generate(opts GenerateOpts) *v1.Pod {
 	pod := &v1.Pod{
 		TypeMeta: metav1.TypeMeta{