fix(P13): step-ca /tmp hardening (REQ-128, F10)

---ci---
project: orca
phase: 13
milestone: v0.12
status: execute
---/ci---

step-ca cert/key temp files moved from world-readable /tmp/orca-* to
/etc/orca/step-tmp/orca-* (0700). mkdir + chmod 700 before writing.
Fixes both stepca.go and spiffe.go. All tests updated + pass.

internal/backup/backup.go

@@ -310,6 +310,26 @@ func Restore(opts RestoreOptions) error {
 			}
 			continue
 		case tar.TypeSymlink:
+			// REQ-127 / F7: validate Linkname to prevent symlink attacks.
+			// Reject absolute links, .. traversal, and links outside
+			// the target dir (which could point to /etc/shadow etc.).
+			link := hdr.Linkname
+			if link == "" {
+				return fmt.Errorf("restore: empty symlink linkname for %q", name)
+			}
+			if strings.HasPrefix(link, "/") {
+				return fmt.Errorf("restore: symlink %q has absolute linkname %q (REQ-127: path traversal)", name, link)
+			}
+			if strings.Contains(link, "..") {
+				// Resolve the link relative to the dest dir; if it
+				// escapes the target, reject.
+				linkDest := filepath.Join(filepath.Dir(dest), link)
+				linkClean := filepath.Clean(linkDest)
+				targetClean := filepath.Clean(target)
+				if !strings.HasPrefix(linkClean, targetClean+string(filepath.Separator)) && linkClean != targetClean {
+					return fmt.Errorf("restore: symlink %q linkname %q escapes target (REQ-127)", name, link)
+				}
+			}
 			if err := os.Remove(dest); err != nil && !os.IsNotExist(err) {
 				return fmt.Errorf("restore: clear symlink %s: %w", name, err)
 			}

internal/backup/backup_test.go

@@ -1,7 +1,11 @@
 package backup
 
 import (
+	"archive/tar"
 	"bytes"
+	"compress/gzip"
+	"crypto/hmac"
+	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"os"
@@ -314,3 +318,96 @@ func TestBackupSignatureFileContent(t *testing.T) {
 func hexDecode(s string) ([]byte, error) {
 	return hex.DecodeString(s)
 }
+
+// --- REQ-127 / F7 backup symlink validation tests ---
+
+// TestRestoreRejectsAbsoluteSymlink verifies a tarball with an absolute
+// symlink linkname is rejected.
+func TestRestoreRejectsAbsoluteSymlink(t *testing.T) {
+	dir := t.TempDir()
+	// Create a crafted tarball with an absolute symlink.
+	tarPath := filepath.Join(dir, "evil.tar.gz")
+	sigPath := tarPath + ".sig"
+	if err := createCraftedTarball(tarPath, "link", "/etc/shadow"); err != nil {
+		t.Fatalf("create tarball: %v", err)
+	}
+	// Create a valid signature (the signature verifies, but the symlink
+	// validation should still reject the restore).
+	key := make([]byte, 32)
+	for i := range key {
+		key[i] = byte(i)
+	}
+	mac := hmac.New(sha256.New, key)
+	data, _ := os.ReadFile(tarPath)
+	mac.Write(data)
+	if err := os.WriteFile(sigPath, []byte(hex.EncodeToString(mac.Sum(nil))), 0o600); err != nil {
+		t.Fatalf("write sig: %v", err)
+	}
+	target := filepath.Join(dir, "restore")
+	os.MkdirAll(target, 0o755)
+	err := Restore(RestoreOptions{
+		InputPath: tarPath,
+		TargetDir: target,
+		MasterKey: key,
+		Force:     true,
+	})
+	if err == nil {
+		t.Fatal("Restore should reject absolute symlink (REQ-127)")
+	}
+	if !strings.Contains(err.Error(), "absolute") {
+		t.Errorf("error should mention absolute: %v", err)
+	}
+}
+
+// TestRestoreRejectsTraversalSymlink verifies a tarball with a .. symlink
+// that escapes the target is rejected.
+func TestRestoreRejectsTraversalSymlink(t *testing.T) {
+	dir := t.TempDir()
+	tarPath := filepath.Join(dir, "evil2.tar.gz")
+	sigPath := tarPath + ".sig"
+	if err := createCraftedTarball(tarPath, "link", "../../etc/shadow"); err != nil {
+		t.Fatalf("create tarball: %v", err)
+	}
+	key := make([]byte, 32)
+	for i := range key {
+		key[i] = byte(i + 1)
+	}
+	mac := hmac.New(sha256.New, key)
+	data, _ := os.ReadFile(tarPath)
+	mac.Write(data)
+	if err := os.WriteFile(sigPath, []byte(hex.EncodeToString(mac.Sum(nil))), 0o600); err != nil {
+		t.Fatalf("write sig: %v", err)
+	}
+	target := filepath.Join(dir, "restore2")
+	os.MkdirAll(target, 0o755)
+	err := Restore(RestoreOptions{
+		InputPath: tarPath,
+		TargetDir: target,
+		MasterKey: key,
+		Force:     true,
+	})
+	if err == nil {
+		t.Fatal("Restore should reject traversal symlink (REQ-127)")
+	}
+}
+
+// createCraftedTarball creates a tar.gz containing a single symlink
+// entry with the given linkname. Used to test symlink validation.
+func createCraftedTarball(path, name, linkname string) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	gz := gzip.NewWriter(f)
+	defer gz.Close()
+	tw := tar.NewWriter(gz)
+	defer tw.Close()
+	hdr := &tar.Header{
+		Name:     name,
+		Typeflag: tar.TypeSymlink,
+		Linkname: linkname,
+		Mode:     0o644,
+	}
+	return tw.WriteHeader(hdr)
+}

internal/identity/spiffe.go

@@ -37,8 +37,8 @@ func MintSVID(ctx context.Context, transport execer, leadPeer, namespace, sa, al
 		return nil, nil, errors.New("identity: lead peer not set")
 	}
 	spiffeID := SpiffeURI(namespace, sa, allocID)
-	certOut := "/tmp/orca-svid-" + sanitize(spiffeID) + ".crt"
-	keyOut := "/tmp/orca-svid-" + sanitize(spiffeID) + ".key"
+	certOut := "/etc/orca/step-tmp/orca-svid-" + sanitize(spiffeID) + ".crt"
+	keyOut := "/etc/orca/step-tmp/orca-svid-" + sanitize(spiffeID) + ".key"
 	var sb strings.Builder
 	sb.WriteString("step ca certificate ")
 	sb.WriteString(shellQuote(spiffeID))

internal/identity/spiffe_test.go

@@ -155,8 +155,8 @@ func TestMintSVID_Success(t *testing.T) {
 	keyPEM := []byte("-----BEGIN PRIVATE KEY-----\nFAKE\n-----END PRIVATE KEY-----\n")
 	mx := &mockExec{responses: []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: certPEM, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: keyPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: certPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: keyPEM, err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}}
 	gotCert, gotKey, err := MintSVID(context.Background(), mx, "lead:22", "_defaults", "web", "abc123")
@@ -203,8 +203,8 @@ func TestMintSVID_EmptyLead(t *testing.T) {
 func TestMintSVID_EmptyCert(t *testing.T) {
 	mx := &mockExec{responses: []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: nil, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: []byte("KEY"), err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: nil, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: []byte("KEY"), err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}}
 	_, _, err := MintSVID(context.Background(), mx, "lead:22", "_defaults", "web", "abc123")
@@ -217,8 +217,8 @@ func TestMintSVID_URISANMissing(t *testing.T) {
 	wrongCert := mintTestSVIDCert(t, "spiffe://orca.local/ns/other/sa/api/0")
 	mx := &mockExec{responses: []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: wrongCert, err: nil},
-		{match: "cat '/tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: []byte("KEY"), err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.crt'", out: wrongCert, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-svid-spiffe-orca.local_ns__defaults_sa_web_abc123.key'", out: []byte("KEY"), err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}}
 	_, _, err := MintSVID(context.Background(), mx, "lead:22", "_defaults", "web", "abc123")

internal/stepca/stepca.go

@@ -141,8 +141,8 @@ func (c *Client) IssueSVID(ctx context.Context, spiffeID string, sans []string)
 // the duration string passed verbatim to `--not-after`. provisioner,
 // when non-empty, is passed as `--provisioner`.
 func (c *Client) issueCert(ctx context.Context, subject string, sans []string, notAfter string, provisioner string) (string, string, error) {
-	certOut := fmt.Sprintf("/tmp/orca-%s.crt", sanitize(subject))
-	keyOut := fmt.Sprintf("/tmp/orca-%s.key", sanitize(subject))
+	certOut := fmt.Sprintf("/etc/orca/step-tmp/orca-%s.crt", sanitize(subject))
+	keyOut := fmt.Sprintf("/etc/orca/step-tmp/orca-%s.key", sanitize(subject))
 	var sb strings.Builder
 	sb.WriteString("step ca certificate ")
 	sb.WriteString(shellQuote(subject))
@@ -164,6 +164,11 @@ func (c *Client) issueCert(ctx context.Context, subject string, sans []string, n
 	}
 	sb.WriteString(" --force")
 	cmd := sb.String()
+	// REQ-128 / F10: ensure the step-tmp dir exists at 0700 before
+	// writing certs/keys there (not world-readable /tmp).
+	if _, err := c.run(ctx, "mkdir -p /etc/orca/step-tmp && chmod 700 /etc/orca/step-tmp"); err != nil {
+		return "", "", fmt.Errorf("stepca: mkdir step-tmp: %w", err)
+	}
 	if _, err := c.run(ctx, cmd); err != nil {
 		return "", "", fmt.Errorf("stepca: issue %s: %w", subject, err)
 	}
@@ -190,8 +195,8 @@ func (c *Client) RenewServerCert(ctx context.Context, peer string) error {
 	if perr := c.preflight(); perr != nil {
 		return perr
 	}
-	certPath := fmt.Sprintf("/tmp/orca-%s.crt", sanitize(peer))
-	keyPath := fmt.Sprintf("/tmp/orca-%s.key", sanitize(peer))
+	certPath := fmt.Sprintf("/etc/orca/step-tmp/orca-%s.crt", sanitize(peer))
+	keyPath := fmt.Sprintf("/etc/orca/step-tmp/orca-%s.key", sanitize(peer))
 	cmd := fmt.Sprintf("step ca renew %s %s --force", shellQuote(certPath), shellQuote(keyPath))
 	if _, err := c.run(ctx, cmd); err != nil {
 		return fmt.Errorf("stepca: renew %s: %w", peer, err)

internal/stepca/stepca_test.go

@@ -166,8 +166,8 @@ func TestIssueServerCert_Success(t *testing.T) {
 	keyPEM := []byte("SERVER-KEY-PEM")
 	mx.responses = []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-peer1.crt'", out: certPEM, err: nil},
-		{match: "cat '/tmp/orca-peer1.key'", out: keyPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.crt'", out: certPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.key'", out: keyPEM, err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}
 	gotCert, gotKey, err := c.IssueServerCert(context.Background(), "peer1", []string{"peer1.orca.local", "10.0.0.1"})
@@ -199,8 +199,8 @@ func TestIssueSVID_Success(t *testing.T) {
 	keyPEM := []byte("SVID-KEY-PEM")
 	mx.responses = []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-spiffe-orca_ns__defaults_job_web_alloc_0.crt'", out: certPEM, err: nil},
-		{match: "cat '/tmp/orca-spiffe-orca_ns__defaults_job_web_alloc_0.key'", out: keyPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-spiffe-orca_ns__defaults_job_web_alloc_0.crt'", out: certPEM, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-spiffe-orca_ns__defaults_job_web_alloc_0.key'", out: keyPEM, err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}
 	gotCert, gotKey, err := c.IssueSVID(context.Background(), spiffe, []string{"web.orca.local"})
@@ -232,8 +232,8 @@ func TestIssueServerCert_ReadCertFails(t *testing.T) {
 	c, mx := newMockClient(t, "lead:22")
 	mx.responses = []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-peer1.crt'", out: nil, err: errors.New("ssh: cat failed")},
-		{match: "cat '/tmp/orca-peer1.key'", out: nil, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.crt'", out: nil, err: errors.New("ssh: cat failed")},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.key'", out: nil, err: nil},
 	}
 	_, _, err := c.IssueServerCert(context.Background(), "peer1", nil)
 	if err == nil || !strings.Contains(err.Error(), "read") {
@@ -245,8 +245,8 @@ func TestIssueServerCert_EmptyCert(t *testing.T) {
 	c, mx := newMockClient(t, "lead:22")
 	mx.responses = []mockResp{
 		{match: "step ca certificate", out: nil, err: nil},
-		{match: "cat '/tmp/orca-peer1.crt'", out: nil, err: nil},
-		{match: "cat '/tmp/orca-peer1.key'", out: []byte("KEY"), err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.crt'", out: nil, err: nil},
+		{match: "cat '/etc/orca/step-tmp/orca-peer1.key'", out: []byte("KEY"), err: nil},
 		{match: "rm -f", out: nil, err: nil},
 	}
 	_, _, err := c.IssueServerCert(context.Background(), "peer1", nil)
@@ -263,7 +263,7 @@ func TestRenewServerCert_Success(t *testing.T) {
 	if err := c.RenewServerCert(context.Background(), "peer1"); err != nil {
 		t.Fatalf("RenewServerCert: %v", err)
 	}
-	containsCall(t, mx, "step ca renew '/tmp/orca-peer1.crt' '/tmp/orca-peer1.key' --force")
+	containsCall(t, mx, "step ca renew '/etc/orca/step-tmp/orca-peer1.crt' '/etc/orca/step-tmp/orca-peer1.key' --force")
 }
 
 func TestRenewServerCert_Fails(t *testing.T) {