R-861: narrow the agent's root grants — exact sudo patterns, felhom-priv-apply content checker, fixed hook/parent files in the bundle, signed self-update verified as root, escrow root reads pinned

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

cmd/felhom-agent/main.go

@@ -22,6 +22,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
+	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -2697,6 +2698,9 @@ func (e *escrowCeremonyErr) Error() string { return e.err.Error() }
 // restic password auto-attach), Create (R + self-verified blob), wipe the staged secret, upload
 // when asked. It PRINTS NOTHING — the output-mode shells own every byte of stdout/stderr. R is
 // returned for the caller to surface exactly once; escrow.Create never logs it and neither do we.
+// pbsStorageIDRe is a PVE storage id (letters, digits, '-', '_', '.'; starts with a letter) — never a path (R-861).
+var pbsStorageIDRe = regexp.MustCompile(`^[A-Za-z][A-Za-z0-9_.-]{0,63}$`)
+
 func escrowCeremony(ctx context.Context, cfg config.Config, logger *slog.Logger, opts escrowCeremonyOpts) (escrowCeremonyOutcome, *escrowCeremonyErr) {
 	var out escrowCeremonyOutcome
 	storage := opts.storage
@@ -2706,6 +2710,16 @@ func escrowCeremony(ctx context.Context, cfg config.Config, logger *slog.Logger,
 	if storage == "" {
 		return out, &escrowCeremonyErr{kind: "usage", err: fmt.Errorf("selftest=escrow-create requires -storage <pbs-storage-id> (or escrow.pbs_storage_id)")}
 	}
+	// R-861 (v0.146.0): this runs as ROOT through FELHOM_ESCROW, but agent.json is owned by the agent user. So the
+	// paths a root run reads never come from it: the PVE secret dir and the WireGuard state dir are the fixed defaults,
+	// and the storage id is a plain PVE id (no slash, no dot-dot) — a crafted id or dir would read another root file.
+	if os.Geteuid() == 0 {
+		cfg.Backup.PBSSecretDir = ""
+		cfg.WGTunnel.StateDir = ""
+	}
+	if !pbsStorageIDRe.MatchString(storage) {
+		return out, &escrowCeremonyErr{kind: "usage", err: fmt.Errorf("selftest=escrow-create: storage id %q is not a plain PVE storage id", storage)}
+	}
 	out.Storage = storage
 	keyPath := cfg.Backup.PBSEncKeyPath(storage)
 	if _, err := os.Stat(keyPath); err != nil {

cmd/felhom-agent/r861_escrow_storage_id_test.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"context"
+	"io"
+	"log/slog"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/config"
+)
+
+// R-861 (agent v0.146.0): the root escrow ceremony builds a file path from the storage id; an id that is a path is
+// refused before anything is read. RED-PROOF: drop the pbsStorageIDRe check → the "../" ids reach the key stat and
+// come back as a "setup" error instead of "usage".
+func TestEscrowCeremony_StorageIDIsNeverAPath(t *testing.T) {
+	lg := slog.New(slog.NewTextHandler(io.Discard, nil))
+	for _, id := range []string{"../../../etc/shadow", "a/b", "/etc/pve/priv/x", ".hidden", ""} {
+		cfg := config.Default()
+		cfg.Escrow.PBSStorageID = "" // the flag decides here
+		_, e := escrowCeremony(context.Background(), cfg, lg, escrowCeremonyOpts{storage: id})
+		if e == nil || e.kind != "usage" {
+			t.Errorf("storage id %q was not refused as usage (got %+v)", id, e)
+		}
+	}
+	cfg := config.Default()
+	cfg.Backup.PBSSecretDir = t.TempDir()
+	_, e := escrowCeremony(context.Background(), cfg, lg, escrowCeremonyOpts{storage: "felhom-pbs"})
+	if e == nil || e.kind != "setup" {
+		t.Fatalf("control: a plain id must pass the check and fail later on the missing key (setup), got %+v", e)
+	}
+}