Support attaching the kernel persistent keyring to an existing keyrin…

…g (for example, session keyring).

Currently, this will always use the persistent keyring associated with the UID executing the process. Specifying UID is supportable but use case unclear.

The AttachPersistent() function will return a Keyring pointing to the kernel persistent keyring, or an error.

keyring.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build linux
 // +build linux
 
 // A Go interface to linux kernel keyrings (keyctl interface)
@@ -21,6 +22,7 @@ type Keyring interface {
 	Add(string, []byte) (*Key, error)
 	Search(string) (*Key, error)
 	SetDefaultTimeout(uint)
+	AttachPersistent() (Keyring, error)
 }
 
 // Named keyrings are user-created keyrings linked to a parent keyring. The
@@ -93,6 +95,13 @@ func (kr *keyring) Search(name string) (*Key, error) {
 	return nil, err
 }
 
+// AttachPersistent attaches the current executing context's persistent
+// keyring to this keyring. See persistent-keyring(7) for more info.
+// It returns either an error, or the persistent Keyring.
+func (kr *keyring) AttachPersistent() (Keyring, error) {
+	return attachPersistent(kr.id)
+}
+
 // Return the current login session keyring
 func SessionKeyring() (Keyring, error) {
 	return newKeyring(keySpecSessionKeyring)

keyring_test.go

@@ -112,6 +112,18 @@ func TestCreateKeyring(t *testing.T) {
 	}
 }
 
+func TestAttachPersistentKeyring(t *testing.T) {
+	kr, err := SessionKeyring()
+	if err != nil {
+		t.Fatalf("unexpected test failure: could not create session keyring: %v", err)
+	}
+	pkr, err := kr.AttachPersistent()
+	if err != nil {
+		t.Fatalf("unexpected test failure: could not attach persistent keyring: %v", err)
+	}
+	t.Logf("found persistent keyring %d", pkr.Id())
+}
+
 func TestCreateNestedKeyring(t *testing.T) {
 	ring := helperTestCreateKeyring(nil, "", t)
 

sys_linux.go

@@ -37,6 +37,12 @@ const (
 	keyctlSetReqKeyKeyring
 	keyctlSetTimeout
 	keyctlAssumeAuthority
+	keyctlGetSecurity
+	keyctlSessionToParent
+	keyctlReject
+	keyctlInstantiateIOV
+	keyctlInvalidate
+	keyctlGetPersistent
 )
 
 var debugSyscalls bool
@@ -81,6 +87,8 @@ func (cmd keyctlCommand) String() string {
 		return "keyctlSetTimeout"
 	case keyctlAssumeAuthority:
 		return "keyctlAssumeAuthority"
+	case keyctlGetPersistent:
+		return "keyctlGetPersistent"
 	}
 	panic("bad arg")
 }
@@ -294,3 +302,12 @@ func updateKey(id keyId, payload []byte) error {
 	}
 	return nil
 }
+
+func attachPersistent(id keyId) (*keyring, error) {
+	uid := int32(-1)
+	r1, _, errno := syscall.Syscall(syscall_keyctl, uintptr(keyctlGetPersistent), uintptr(uid), uintptr(id))
+	if errno != 0 {
+		return nil, errno
+	}
+	return &keyring{id: keyId(r1)}, nil
+}