fix(workloads): world executors run as root so game-image worlds are readable

A live backup drill on test-one failed: 'tar walk: open
/world/world/level.dat: permission denied'. The world volume belongs to
the game image's own UID (root for every Paper image we ship), and Paper
saves level.dat mode 0600 — a fixed uid-1000 executor can neither read
it (backup/reaper archive) nor overwrite it (restore). The same identity
silently broke on-demand backups, restores, and the reaper for every
server that had saved once.

Run the backup Job, restore Job, file Job, and the reaper pod as root
with DAC_OVERRIDE on top of drop-ALL — the same owner-matching precedent
as the operator's forwarding-init container; DAC_OVERRIDE extends it to
game images whose UID is neither root nor ours. FSGroup is omitted when
zero so a root executor never chgrps the world volume. Shape tests
updated for the new identity.

internal/backupjob/backup.go

@@ -87,9 +87,14 @@ type Config struct {
 	// CPULimit / MemLimit cap the backup container.
 	CPULimit string
 	MemLimit string
-	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. FSGroup MUST
-	// match the operator StatefulSet's runtime group so the read-only world mount is
-	// readable by this Pod's uid.
+	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. They default
+	// to ROOT (0:0) for the same reason the operator's forwarding-init container
+	// runs as root: the world volume is written by the game image's own UID (root
+	// for every Paper image we ship), and Paper saves files a non-root uid can
+	// never read — level.dat is written mode 0600 (tar walk: permission denied,
+	// verified live). DAC_OVERRIDE on the container covers images whose UID is
+	// neither root nor ours. Set 0/0/0 explicitly for root; FSGroup is omitted
+	// when zero.
 	RunAsUser  int64
 	RunAsGroup int64
 	FSGroup    int64
@@ -111,7 +116,6 @@ const (
 	defaultDeadline       = 30 * time.Minute
 	defaultCPULimit       = "1"
 	defaultMemLimit       = "1Gi"
-	defaultRunAsID        = int64(1000)
 	defaultTTL            = 10 * time.Minute
 )
 
@@ -145,15 +149,6 @@ func (c Config) withDefaults() Config {
 	if c.MemLimit == "" {
 		c.MemLimit = defaultMemLimit
 	}
-	if c.RunAsUser == 0 {
-		c.RunAsUser = defaultRunAsID
-	}
-	if c.RunAsGroup == 0 {
-		c.RunAsGroup = defaultRunAsID
-	}
-	if c.FSGroup == 0 {
-		c.FSGroup = defaultRunAsID
-	}
 	if c.TTLAfterFinished <= 0 {
 		c.TTLAfterFinished = defaultTTL
 	}

internal/backupjob/jobspec.go

@@ -148,7 +148,14 @@ func BackupJob(p JobParams) (*batchv1.Job, error) {
 			Privileged:               boolPtr(false),
 			AllowPrivilegeEscalation: boolPtr(false),
 			ReadOnlyRootFilesystem:   boolPtr(true),
-			Capabilities:             &corev1.Capabilities{Drop: []corev1.Capability{"ALL"}},
+			// DAC_OVERRIDE is granted on top of dropping ALL: the pod runs as root,
+			// but the world may have been written by a game image whose UID is
+			// neither root nor ours, and Paper's own files are mode 0600. It is the
+			// minimal extra power that makes the archive read every world shape.
+			Capabilities: &corev1.Capabilities{
+				Drop: []corev1.Capability{"ALL"},
+				Add:  []corev1.Capability{"DAC_OVERRIDE"},
+			},
 		},
 	}
 
@@ -175,13 +182,12 @@ func BackupJob(p JobParams) (*batchv1.Job, error) {
 					RestartPolicy:                corev1.RestartPolicyNever,
 					ServiceAccountName:           p.ServiceAccount,
 					AutomountServiceAccountToken: boolPtr(false),
-					SecurityContext: &corev1.PodSecurityContext{
-						RunAsNonRoot: boolPtr(true),
-						RunAsUser:    int64Ptr(p.RunAsUser),
-						RunAsGroup:   int64Ptr(p.RunAsGroup),
-						FSGroup:      int64Ptr(p.FSGroup),
-					},
-					Containers: []corev1.Container{container},
+					// Root by default (see Config.RunAsUser): the world volume's
+					// owner is the game image's UID, so only an owner-matching or
+					// DAC-overriding uid can read it. FSGroup is omitted when unset
+					// so a root pod never triggers a volume chgrp.
+					SecurityContext: backupPodSecurityContext(p),
+					Containers:      []corev1.Container{container},
 					Volumes: []corev1.Volume{
 						{
 							Name: worldVolume,
@@ -240,3 +246,20 @@ func resourceLimits(cpu, mem string) (corev1.ResourceList, error) {
 func boolPtr(b bool) *bool    { return &b }
 func int32Ptr(i int32) *int32 { return &i }
 func int64Ptr(i int64) *int64 { return &i }
+
+// backupPodSecurityContext pins the Pod identity. RunAsNonRoot is false because
+// the default identity is root: worlds are owned by the game image's UID (root
+// for the images we ship), and Paper writes mode-0600 files a non-root reader
+// cannot open. FSGroup stays unset unless configured — a root executor must not
+// needlessly chgrp the world volume.
+func backupPodSecurityContext(p JobParams) *corev1.PodSecurityContext {
+	sc := &corev1.PodSecurityContext{
+		RunAsNonRoot: boolPtr(false),
+		RunAsUser:    int64Ptr(p.RunAsUser),
+		RunAsGroup:   int64Ptr(p.RunAsGroup),
+	}
+	if p.FSGroup > 0 {
+		sc.FSGroup = int64Ptr(p.FSGroup)
+	}
+	return sc
+}

internal/backupjob/jobspec_test.go

@@ -23,9 +23,9 @@ func sampleJobParams() JobParams {
 		Deadline:         30 * time.Minute,
 		CPULimit:         "1",
 		MemLimit:         "1Gi",
-		RunAsUser:        1000,
-		RunAsGroup:       1000,
-		FSGroup:          1000,
+		RunAsUser:        0,
+		RunAsGroup:       0,
+		FSGroup:          0,
 		TTLAfterFinished: 10 * time.Minute,
 	}
 }
@@ -109,13 +109,30 @@ func TestBackupJobMountsTwoPVCsPlusConfigSecretOnly(t *testing.T) {
 	}
 }
 
-// The backup container is hardened exactly like the restore/build Job containers:
-// no privilege, no escalation, read-only root fs, drop ALL capabilities.
+// The backup container is hardened like the restore/build Job containers: no
+// privilege, no escalation, read-only root fs, ALL capabilities dropped — plus
+// DAC_OVERRIDE, because the Pod runs as root and the world may have been written
+// by a game image with a different UID (verified live: a uid-1000 executor cannot
+// read Paper's mode-0600 level.dat).
 func TestBackupJobContainerIsHardened(t *testing.T) {
 	job, err := BackupJob(sampleJobParams())
 	if err != nil {
 		t.Fatalf("BackupJob: %v", err)
 	}
+	pod := job.Spec.Template.Spec
+	if pod.SecurityContext == nil {
+		t.Fatal("pod SecurityContext is nil")
+	}
+	if pod.SecurityContext.RunAsNonRoot == nil || *pod.SecurityContext.RunAsNonRoot {
+		t.Error("pod must NOT require non-root: root is the owner-matching default for game-image worlds")
+	}
+	if pod.SecurityContext.RunAsUser == nil || *pod.SecurityContext.RunAsUser != 0 ||
+		pod.SecurityContext.RunAsGroup == nil || *pod.SecurityContext.RunAsGroup != 0 {
+		t.Errorf("pod must run as 0:0 by default, got %+v", pod.SecurityContext)
+	}
+	if pod.SecurityContext.FSGroup != nil {
+		t.Error("fsGroup must stay unset when zero (a root executor must not chgrp the world volume)")
+	}
 	sc := job.Spec.Template.Spec.Containers[0].SecurityContext
 	if sc == nil {
 		t.Fatal("container SecurityContext is nil")
@@ -132,6 +149,9 @@ func TestBackupJobContainerIsHardened(t *testing.T) {
 	if sc.Capabilities == nil || len(sc.Capabilities.Drop) != 1 || sc.Capabilities.Drop[0] != "ALL" {
 		t.Error("capabilities must drop ALL")
 	}
+	if len(sc.Capabilities.Add) != 1 || sc.Capabilities.Add[0] != "DAC_OVERRIDE" {
+		t.Errorf("capabilities must add exactly DAC_OVERRIDE, got %v", sc.Capabilities.Add)
+	}
 }
 
 // One-shot: a wedged archive must not loop, and a deadline caps it.

internal/fileedit/editor.go

@@ -112,9 +112,12 @@ type Config struct {
 	// CPULimit / MemLimit cap the container.
 	CPULimit string
 	MemLimit string
-	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. FSGroup MUST
-	// match the operator StatefulSet's runtime group, or a file this Pod writes
-	// would be unreadable by the minecraft server that later mounts the same PVC.
+	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. They default
+	// to ROOT (0:0): the world volume is written by the game image's own UID (root
+	// for the images we ship), and Paper saves mode-0600 files a non-root editor
+	// can neither read nor rewrite (level.dat). DAC_OVERRIDE on the container
+	// covers images whose UID is neither root nor ours; FSGroup is omitted when
+	// zero.
 	RunAsUser  int64
 	RunAsGroup int64
 	FSGroup    int64
@@ -136,7 +139,6 @@ const (
 	defaultTimeout        = 90 * time.Second
 	defaultCPULimit       = "500m"
 	defaultMemLimit       = "256Mi"
-	defaultRunAsID        = int64(1000)
 	defaultTTL            = 2 * time.Minute
 )
 
@@ -164,15 +166,6 @@ func (c Config) withDefaults() Config {
 	if c.MemLimit == "" {
 		c.MemLimit = defaultMemLimit
 	}
-	if c.RunAsUser == 0 {
-		c.RunAsUser = defaultRunAsID
-	}
-	if c.RunAsGroup == 0 {
-		c.RunAsGroup = defaultRunAsID
-	}
-	if c.FSGroup == 0 {
-		c.FSGroup = defaultRunAsID
-	}
 	if c.TTLAfterFinished <= 0 {
 		c.TTLAfterFinished = defaultTTL
 	}

internal/fileedit/jobspec.go

@@ -165,7 +165,13 @@ func FilesJob(p JobParams) (*batchv1.Job, error) {
 			Privileged:               boolPtr(false),
 			AllowPrivilegeEscalation: boolPtr(false),
 			ReadOnlyRootFilesystem:   boolPtr(true),
-			Capabilities:             &corev1.Capabilities{Drop: []corev1.Capability{"ALL"}},
+			// Root + DAC_OVERRIDE (see Config.RunAsUser): the file the editor is
+			// asked to touch may be a mode-0600 file the game wrote as its own
+			// (image) UID — level.dat — which a fixed non-root uid cannot open.
+			Capabilities: &corev1.Capabilities{
+				Drop: []corev1.Capability{"ALL"},
+				Add:  []corev1.Capability{"DAC_OVERRIDE"},
+			},
 		},
 	}
 
@@ -199,13 +205,8 @@ func FilesJob(p JobParams) (*batchv1.Job, error) {
 					RestartPolicy:                corev1.RestartPolicyNever,
 					ServiceAccountName:           p.ServiceAccount,
 					AutomountServiceAccountToken: boolPtr(false),
-					SecurityContext: &corev1.PodSecurityContext{
-						RunAsNonRoot: boolPtr(true),
-						RunAsUser:    int64Ptr(p.RunAsUser),
-						RunAsGroup:   int64Ptr(p.RunAsGroup),
-						FSGroup:      int64Ptr(p.FSGroup),
-					},
-					Containers: []corev1.Container{container},
+					SecurityContext:              filesPodSecurityContext(p),
+					Containers:                   []corev1.Container{container},
 					Volumes: []corev1.Volume{{
 						Name: worldVolume,
 						VolumeSource: corev1.VolumeSource{
@@ -247,3 +248,19 @@ func resourceLimits(cpu, mem string) (corev1.ResourceList, error) {
 func boolPtr(b bool) *bool    { return &b }
 func int32Ptr(i int32) *int32 { return &i }
 func int64Ptr(i int64) *int64 { return &i }
+
+// filesPodSecurityContext pins the Pod identity. Root by default: the world
+// volume belongs to the game image's UID (root for the images we ship) and its
+// mode-0600 files (level.dat) are otherwise unreadable/unwritable. FSGroup is
+// only rendered when configured so a root executor never chgrps the volume.
+func filesPodSecurityContext(p JobParams) *corev1.PodSecurityContext {
+	sc := &corev1.PodSecurityContext{
+		RunAsNonRoot: boolPtr(false),
+		RunAsUser:    int64Ptr(p.RunAsUser),
+		RunAsGroup:   int64Ptr(p.RunAsGroup),
+	}
+	if p.FSGroup > 0 {
+		sc.FSGroup = int64Ptr(p.FSGroup)
+	}
+	return sc
+}

internal/fileedit/jobspec_test.go

@@ -23,9 +23,9 @@ func testParams(op string) JobParams {
 		Deadline:         2 * time.Minute,
 		CPULimit:         "500m",
 		MemLimit:         "256Mi",
-		RunAsUser:        1000,
-		RunAsGroup:       1000,
-		FSGroup:          1000,
+		RunAsUser:        0,
+		RunAsGroup:       0,
+		FSGroup:          0,
 		TTLAfterFinished: 2 * time.Minute,
 	}
 }
@@ -64,17 +64,19 @@ func TestFilesJobIsolation(t *testing.T) {
 		}
 	})
 
-	t.Run("runs non-root with the operator's runtime identity", func(t *testing.T) {
+	t.Run("runs as root, the owner-matching identity for game-image worlds", func(t *testing.T) {
 		sc := spec.SecurityContext
-		if sc == nil || sc.RunAsNonRoot == nil || !*sc.RunAsNonRoot {
-			t.Fatal("RunAsNonRoot must be true")
+		if sc == nil || sc.RunAsNonRoot == nil || *sc.RunAsNonRoot {
+			t.Fatal("RunAsNonRoot must be false: root is the owner-matching default for game-image worlds")
 		}
-		// FSGroup must match the minecraft server's group or a file this Pod writes
-		// would be unreadable by the server that later mounts the same volume.
-		if sc.RunAsUser == nil || *sc.RunAsUser != 1000 ||
-			sc.RunAsGroup == nil || *sc.RunAsGroup != 1000 ||
-			sc.FSGroup == nil || *sc.FSGroup != 1000 {
-			t.Fatalf("uid/gid/fsGroup must all be 1000, got %+v", sc)
+		// Root because the world volume belongs to the game image's UID and Paper
+		// saves mode-0600 files a fixed non-root editor cannot open.
+		if sc.RunAsUser == nil || *sc.RunAsUser != 0 ||
+			sc.RunAsGroup == nil || *sc.RunAsGroup != 0 {
+			t.Fatalf("uid/gid must be 0:0 by default, got %+v", sc)
+		}
+		if sc.FSGroup != nil {
+			t.Fatalf("fsGroup must stay unset when zero, got %+v", sc.FSGroup)
 		}
 	})
 
@@ -98,6 +100,9 @@ func TestFilesJobIsolation(t *testing.T) {
 		if sc.Capabilities == nil || len(sc.Capabilities.Drop) != 1 || sc.Capabilities.Drop[0] != "ALL" {
 			t.Fatalf("capabilities must drop ALL, got %+v", sc.Capabilities)
 		}
+		if len(sc.Capabilities.Add) != 1 || sc.Capabilities.Add[0] != "DAC_OVERRIDE" {
+			t.Fatalf("capabilities must add exactly DAC_OVERRIDE, got %+v", sc.Capabilities.Add)
+		}
 	})
 
 	t.Run("is one-shot, deadlined, and self-collecting", func(t *testing.T) {

internal/platform/workloads.go

@@ -557,7 +557,7 @@ func reaperCronJob(p Params) *batchv1.CronJob {
 			{Name: tmpVolume, MountPath: "/tmp"},
 		},
 		Resources:       controlPlaneResources(),
-		SecurityContext: hardenedContainerSecurityContext(),
+		SecurityContext: reaperContainerSecurityContext(),
 	}
 
 	volumes := []corev1.Volume{
@@ -609,7 +609,7 @@ func reaperCronJob(p Params) *batchv1.CronJob {
 							ServiceAccountName: SAReaper,
 							PriorityClassName:  controlPlanePriorityName,
 							RestartPolicy:      corev1.RestartPolicyNever,
-							SecurityContext:    hardenedPodSecurityContext(),
+							SecurityContext:    reaperPodSecurityContext(),
 							Containers:         []corev1.Container{container},
 							Volumes:            volumes,
 						},
@@ -842,9 +842,11 @@ func controlPlaneResources() corev1.ResourceRequirements {
 	}
 }
 
-// hardenedPodSecurityContext is the pod-level hardening shared by every workload
-// here: run as a fixed non-root uid/gid with a matching fsGroup (so the registry
-// can write its group-owned PVC) and the RuntimeDefault seccomp profile.
+// hardenedPodSecurityContext is the pod-level hardening shared by the
+// control-plane workloads (api, operator, registry — the world-touching reaper
+// uses reaperPodSecurityContext instead): run as a fixed non-root uid/gid with a
+// matching fsGroup (so the registry can write its group-owned PVC) and the
+// RuntimeDefault seccomp profile.
 //
 // SHAPE-ASSERTED, runtime-unverified: this asserts the images can run as
 // nonRootUID. The felis image is built to; registry:2 (CNCF Distribution) can,
@@ -860,6 +862,36 @@ func hardenedPodSecurityContext() *corev1.PodSecurityContext {
 	}
 }
 
+// reaperPodSecurityContext is the reaper's Pod identity: ROOT, deliberately NOT
+// the control-plane's non-root uid. Its HostPath mount IS the live storage root,
+// and the world directories beneath it (and the files inside them) are written
+// by the game image's own UID — root for every Paper image we ship — with
+// Paper's mode-0600 saves (level.dat) included. Only an owner-matching uid (or
+// DAC override, granted on the container below) can archive and delete those
+// worlds; the uid-1000 convention failed them with `permission denied`
+// (verified live). Same rationale as the operator's forwarding-init container.
+func reaperPodSecurityContext() *corev1.PodSecurityContext {
+	return &corev1.PodSecurityContext{
+		RunAsNonRoot:   boolPtr(false),
+		RunAsUser:      int64Ptr(0),
+		RunAsGroup:     int64Ptr(0),
+		SeccompProfile: &corev1.SeccompProfile{Type: corev1.SeccompProfileTypeRuntimeDefault},
+	}
+}
+
+// reaperContainerSecurityContext is hardenedContainerSecurityContext plus
+// DAC_OVERRIDE: with root's caps dropped, root can read only files it owns, and
+// a world may have been written by a game image whose UID is neither root nor
+// ours. DAC_OVERRIDE restores exactly the file-mode bypass the archive needs.
+func reaperContainerSecurityContext() *corev1.SecurityContext {
+	sc := hardenedContainerSecurityContext()
+	sc.Capabilities = &corev1.Capabilities{
+		Drop: []corev1.Capability{"ALL"},
+		Add:  []corev1.Capability{"DAC_OVERRIDE"},
+	}
+	return sc
+}
+
 // hardenedContainerSecurityContext mirrors the build/restore Job containers: no
 // privilege, no escalation, read-only root filesystem (all writes go to the
 // mounted volumes — the config/data mounts and the /tmp emptyDir), drop ALL

internal/platform/workloads_test.go

@@ -704,9 +704,15 @@ func TestReaperCronJob_Shape(t *testing.T) {
 		t.Errorf("reaper pod must auto-mount its SA token (got AutomountServiceAccountToken=%v); it needs the API", *ps.AutomountServiceAccountToken)
 	}
 
-	// Hardening mirrors the other control-plane pods.
-	if ps.SecurityContext == nil || ps.SecurityContext.RunAsNonRoot == nil || !*ps.SecurityContext.RunAsNonRoot {
-		t.Error("reaper pod must set runAsNonRoot=true")
+	// The reaper is the one world-touching workload, so its identity is ROOT, not
+	// the control-plane's non-root uid: the worlds it archives and deletes are
+	// written by the game image's own UID (root for the images we ship), including
+	// Paper's mode-0600 files. DAC_OVERRIDE covers images with another UID.
+	if ps.SecurityContext == nil || ps.SecurityContext.RunAsNonRoot == nil || *ps.SecurityContext.RunAsNonRoot {
+		t.Error("reaper pod must NOT require non-root: root is the owner-matching identity for game-image worlds")
+	}
+	if ps.SecurityContext == nil || ps.SecurityContext.RunAsUser == nil || *ps.SecurityContext.RunAsUser != 0 {
+		t.Error("reaper pod must run as uid 0")
 	}
 	if c.SecurityContext == nil || c.SecurityContext.ReadOnlyRootFilesystem == nil || !*c.SecurityContext.ReadOnlyRootFilesystem {
 		t.Error("reaper container must set readOnlyRootFilesystem=true")
@@ -714,6 +720,9 @@ func TestReaperCronJob_Shape(t *testing.T) {
 	if c.SecurityContext == nil || c.SecurityContext.Capabilities == nil || len(c.SecurityContext.Capabilities.Drop) == 0 || c.SecurityContext.Capabilities.Drop[0] != "ALL" {
 		t.Error("reaper container must drop ALL capabilities")
 	}
+	if c.SecurityContext == nil || c.SecurityContext.Capabilities == nil || len(c.SecurityContext.Capabilities.Add) != 1 || c.SecurityContext.Capabilities.Add[0] != "DAC_OVERRIDE" {
+		t.Error("reaper container must add exactly DAC_OVERRIDE")
+	}
 
 	// Entrypoint: `/usr/local/bin/felis reaper --config <cfg> --worlds-root /worlds`.
 	if got := append(append([]string{}, c.Command...), c.Args...); !containsSeq(got, []string{felisBinaryPath, "reaper"}) {

internal/restore/jobspec.go

@@ -125,7 +125,14 @@ func RestoreJob(p JobParams) (*batchv1.Job, error) {
 			Privileged:               boolPtr(false),
 			AllowPrivilegeEscalation: boolPtr(false),
 			ReadOnlyRootFilesystem:   boolPtr(true),
-			Capabilities:             &corev1.Capabilities{Drop: []corev1.Capability{"ALL"}},
+			// Root + DAC_OVERRIDE (see restore.Config.RunAsUser): the world is
+			// owned by the game image's UID and Paper's files are mode 0600, so
+			// the restore must bypass file modes to overwrite what the server
+			// wrote — otherwise level.dat is un-restorable.
+			Capabilities: &corev1.Capabilities{
+				Drop: []corev1.Capability{"ALL"},
+				Add:  []corev1.Capability{"DAC_OVERRIDE"},
+			},
 		},
 	}
 
@@ -148,13 +155,8 @@ func RestoreJob(p JobParams) (*batchv1.Job, error) {
 					RestartPolicy:                corev1.RestartPolicyNever,
 					ServiceAccountName:           p.ServiceAccount,
 					AutomountServiceAccountToken: boolPtr(false),
-					SecurityContext: &corev1.PodSecurityContext{
-						RunAsNonRoot: boolPtr(true),
-						RunAsUser:    int64Ptr(p.RunAsUser),
-						RunAsGroup:   int64Ptr(p.RunAsGroup),
-						FSGroup:      int64Ptr(p.FSGroup),
-					},
-					Containers: []corev1.Container{container},
+					SecurityContext:              restorePodSecurityContext(p),
+					Containers:                   []corev1.Container{container},
 					Volumes: []corev1.Volume{
 						{
 							Name: worldVolume,
@@ -221,6 +223,22 @@ func resourceLimits(cpu, mem string) (corev1.ResourceList, error) {
 	}, nil
 }
 
-func boolPtr(b bool) *bool    { return &b }
+func boolPtr(b bool) *bool { return &b }
+
+// restorePodSecurityContext pins the Pod identity. Root by default — the world
+// volume is owned by the game image's UID and Paper writes mode-0600 files, so a
+// fixed non-root executor could neither read nor replace them. FSGroup is only
+// rendered when configured: a root executor must not chgrp the world volume.
+func restorePodSecurityContext(p JobParams) *corev1.PodSecurityContext {
+	sc := &corev1.PodSecurityContext{
+		RunAsNonRoot: boolPtr(false),
+		RunAsUser:    int64Ptr(p.RunAsUser),
+		RunAsGroup:   int64Ptr(p.RunAsGroup),
+	}
+	if p.FSGroup > 0 {
+		sc.FSGroup = int64Ptr(p.FSGroup)
+	}
+	return sc
+}
 func int32Ptr(i int32) *int32 { return &i }
 func int64Ptr(i int64) *int64 { return &i }

internal/restore/jobspec_test.go

@@ -23,9 +23,9 @@ func sampleJobParams() JobParams {
 		Deadline:         30 * time.Minute,
 		CPULimit:         "1",
 		MemLimit:         "1Gi",
-		RunAsUser:        1000,
-		RunAsGroup:       1000,
-		FSGroup:          1000,
+		RunAsUser:        0,
+		RunAsGroup:       0,
+		FSGroup:          0,
 		TTLAfterFinished: 10 * time.Minute,
 	}
 }
@@ -161,19 +161,24 @@ func TestRestoreJobIsBoundedOneShotAndSelfCleaning(t *testing.T) {
 	}
 }
 
-// The container must be non-root, non-privileged, escalation-proof, read-only
-// root, drop ALL caps, and carry resource limits.
+// The Pod runs as root (the world volume belongs to the game image's UID — see
+// restore.Config.RunAsUser), and the container stays non-privileged,
+// escalation-proof, read-only root, ALL caps dropped except DAC_OVERRIDE, with
+// resource limits.
 func TestRestoreJobContainerIsHardened(t *testing.T) {
 	job, err := RestoreJob(sampleJobParams())
 	if err != nil {
 		t.Fatalf("RestoreJob: %v", err)
 	}
 	pod := job.Spec.Template.Spec
-	if pod.SecurityContext == nil || pod.SecurityContext.RunAsNonRoot == nil || !*pod.SecurityContext.RunAsNonRoot {
-		t.Error("pod must set runAsNonRoot=true")
+	if pod.SecurityContext == nil || pod.SecurityContext.RunAsNonRoot == nil || *pod.SecurityContext.RunAsNonRoot {
+		t.Error("pod must NOT require non-root: root is the owner-matching default for game-image worlds")
 	}
-	if pod.SecurityContext == nil || pod.SecurityContext.FSGroup == nil || *pod.SecurityContext.FSGroup != 1000 {
-		t.Error("pod must set an fsGroup so restored files are group-owned by the server identity")
+	if pod.SecurityContext == nil || pod.SecurityContext.RunAsUser == nil || *pod.SecurityContext.RunAsUser != 0 {
+		t.Error("pod must run as uid 0 by default")
+	}
+	if pod.SecurityContext == nil || pod.SecurityContext.FSGroup != nil {
+		t.Error("fsGroup must stay unset when zero (a root executor must not chgrp the world volume)")
 	}
 	c := singleContainer(t, job)
 	sc := c.SecurityContext
@@ -192,6 +197,9 @@ func TestRestoreJobContainerIsHardened(t *testing.T) {
 	if sc.Capabilities == nil || len(sc.Capabilities.Drop) == 0 || string(sc.Capabilities.Drop[0]) != "ALL" {
 		t.Errorf("container must drop ALL capabilities, got %v", sc.Capabilities)
 	}
+	if len(sc.Capabilities.Add) != 1 || sc.Capabilities.Add[0] != "DAC_OVERRIDE" {
+		t.Errorf("container must add exactly DAC_OVERRIDE, got %v", sc.Capabilities.Add)
+	}
 	if c.Resources.Limits.Cpu().IsZero() || c.Resources.Limits.Memory().IsZero() {
 		t.Error("container must carry CPU+memory limits")
 	}

internal/restore/restore.go

@@ -86,11 +86,13 @@ type Config struct {
 	// CPULimit / MemLimit cap the restore container.
 	CPULimit string
 	MemLimit string
-	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. FSGroup in
-	// particular MUST match the operator StatefulSet's runtime group so the files
-	// the restore Pod writes are readable by the minecraft server that later
-	// mounts the same world PVC. The default matches the conventional minecraft
-	// container uid; a deployment that runs minecraft as another id overrides it.
+	// RunAsUser / RunAsGroup / FSGroup are the Pod's runtime identity. They default
+	// to ROOT (0:0) for the same reason the operator's forwarding-init runs as
+	// root: the world volume is written by the game image's own UID (root for the
+	// images we ship), and Paper saves mode-0600 files a non-root writer/reader
+	// cannot replace (a uid-1000 restore cannot overwrite level.dat). DAC_OVERRIDE
+	// on the container covers images whose UID is neither root nor ours; FSGroup
+	// is omitted when zero.
 	RunAsUser  int64
 	RunAsGroup int64
 	FSGroup    int64
@@ -112,7 +114,6 @@ const (
 	defaultDeadline       = 30 * time.Minute
 	defaultCPULimit       = "1"
 	defaultMemLimit       = "1Gi"
-	defaultRunAsID        = int64(1000)
 	defaultTTL            = 10 * time.Minute
 )
 
@@ -143,15 +144,6 @@ func (c Config) withDefaults() Config {
 	if c.MemLimit == "" {
 		c.MemLimit = defaultMemLimit
 	}
-	if c.RunAsUser == 0 {
-		c.RunAsUser = defaultRunAsID
-	}
-	if c.RunAsGroup == 0 {
-		c.RunAsGroup = defaultRunAsID
-	}
-	if c.FSGroup == 0 {
-		c.FSGroup = defaultRunAsID
-	}
 	if c.TTLAfterFinished <= 0 {
 		c.TTLAfterFinished = defaultTTL
 	}