KEYS: Alter use of key instantiation link-to-keyring argument

Alter the use of the key instantiation and negation functions' link-to-keyring
arguments.  Currently this specifies a keyring in the target process to link
the key into, creating the keyring if it doesn't exist.  This, however, can be
a problem for copy-on-write credentials as it means that the instantiating
process can alter the credentials of the requesting process.

This patch alters the behaviour such that:

 (1) If keyctl_instantiate_key() or keyctl_negate_key() are given a specific
     keyring by ID (ringid >= 0), then that keyring will be used.

 (2) If keyctl_instantiate_key() or keyctl_negate_key() are given one of the
     special constants that refer to the requesting process's keyrings
     (KEY_SPEC_*_KEYRING, all <= 0), then:

     (a) If sys_request_key() was given a keyring to use (destringid) then the
     	 key will be attached to that keyring.

     (b) If sys_request_key() was given a NULL keyring, then the key being
     	 instantiated will be attached to the default keyring as set by
     	 keyctl_set_reqkey_keyring().

 (3) No extra link will be made.

Decision point (1) follows current behaviour, and allows those instantiators
who've searched for a specifically named keyring in the requestor's keyring so
as to partition the keys by type to still have their named keyrings.

Decision point (2) allows the requestor to make sure that the key or keys that
get produced by request_key() go where they want, whilst allowing the
instantiator to request that the key is retained.  This is mainly useful for
situations where the instantiator makes a secondary request, the key for which
should be retained by the initial requestor:

	+-----------+        +--------------+        +--------------+
	|           |        |              |        |              |
	| Requestor |------->| Instantiator |------->| Instantiator |
	|           |        |              |        |              |
	+-----------+        +--------------+        +--------------+
	           request_key()           request_key()

This might be useful, for example, in Kerberos, where the requestor requests a
ticket, and then the ticket instantiator requests the TGT, which someone else
then has to go and fetch.  The TGT, however, should be retained in the
keyrings of the requestor, not the first instantiator.  To make this explict
an extra special keyring constant is also added.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 54 insertions, 34 deletions

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 5be6d018759..1c793b7090a 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -40,9 +40,9 @@ struct key_user root_key_user = {
 /*
  * install user and user session keyrings for a particular UID
  */
-static int install_user_keyrings(struct task_struct *tsk)
+int install_user_keyrings(void)
 {
-	struct user_struct *user = tsk->user;
+	struct user_struct *user = current->user;
 	struct key *uid_keyring, *session_keyring;
 	char buf[20];
 	int ret;
@@ -67,7 +67,7 @@ static int install_user_keyrings(struct task_struct *tsk)
 		uid_keyring = find_keyring_by_name(buf, true);
 		if (IS_ERR(uid_keyring)) {
 			uid_keyring = keyring_alloc(buf, user->uid, (gid_t) -1,
-						    tsk, KEY_ALLOC_IN_QUOTA,
+						    current, KEY_ALLOC_IN_QUOTA,
 						    NULL);
 			if (IS_ERR(uid_keyring)) {
 				ret = PTR_ERR(uid_keyring);
@@ -83,7 +83,8 @@ static int install_user_keyrings(struct task_struct *tsk)
 		if (IS_ERR(session_keyring)) {
 			session_keyring =
 				keyring_alloc(buf, user->uid, (gid_t) -1,
-					      tsk, KEY_ALLOC_IN_QUOTA, NULL);
+					      current, KEY_ALLOC_IN_QUOTA,
+					      NULL);
 			if (IS_ERR(session_keyring)) {
 				ret = PTR_ERR(session_keyring);
 				goto error_release;
@@ -146,8 +147,9 @@ void switch_uid_keyring(struct user_struct *new_user)
 /*
  * install a fresh thread keyring, discarding the old one
  */
-int install_thread_keyring(struct task_struct *tsk)
+int install_thread_keyring(void)
 {
+	struct task_struct *tsk = current;
 	struct key *keyring, *old;
 	char buf[20];
 	int ret;
@@ -178,8 +180,9 @@ error:
 /*
  * make sure a process keyring is installed
  */
-int install_process_keyring(struct task_struct *tsk)
+int install_process_keyring(void)
 {
+	struct task_struct *tsk = current;
 	struct key *keyring;
 	char buf[20];
 	int ret;
@@ -218,9 +221,9 @@ error:
  * install a session keyring, discarding the old one
  * - if a keyring is not supplied, an empty one is invented
  */
-static int install_session_keyring(struct task_struct *tsk,
-				   struct key *keyring)
+static int install_session_keyring(struct key *keyring)
 {
+	struct task_struct *tsk = current;
 	unsigned long flags;
 	struct key *old;
 	char buf[20];
@@ -572,93 +575,91 @@ static int lookup_user_key_possessed(const struct key *key, const void *target)
  * - don't create special keyrings unless so requested
  * - partially constructed keys aren't found unless requested
  */
-key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
-			  int create, int partial, key_perm_t perm)
+key_ref_t lookup_user_key(key_serial_t id, int create, int partial,
+			  key_perm_t perm)
 {
+	struct request_key_auth *rka;
+	struct task_struct *t = current;
 	key_ref_t key_ref, skey_ref;
 	struct key *key;
 	int ret;
 
-	if (!context)
-		context = current;
-
 	key_ref = ERR_PTR(-ENOKEY);
 
 	switch (id) {
 	case KEY_SPEC_THREAD_KEYRING:
-		if (!context->thread_keyring) {
+		if (!t->thread_keyring) {
 			if (!create)
 				goto error;
 
-			ret = install_thread_keyring(context);
+			ret = install_thread_keyring();
 			if (ret < 0) {
 				key = ERR_PTR(ret);
 				goto error;
 			}
 		}
 
-		key = context->thread_keyring;
+		key = t->thread_keyring;
 		atomic_inc(&key->usage);
 		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_PROCESS_KEYRING:
-		if (!context->signal->process_keyring) {
+		if (!t->signal->process_keyring) {
 			if (!create)
 				goto error;
 
-			ret = install_process_keyring(context);
+			ret = install_process_keyring();
 			if (ret < 0) {
 				key = ERR_PTR(ret);
 				goto error;
 			}
 		}
 
-		key = context->signal->process_keyring;
+		key = t->signal->process_keyring;
 		atomic_inc(&key->usage);
 		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_SESSION_KEYRING:
-		if (!context->signal->session_keyring) {
+		if (!t->signal->session_keyring) {
 			/* always install a session keyring upon access if one
 			 * doesn't exist yet */
-			ret = install_user_keyrings(context);
+			ret = install_user_keyrings();
 			if (ret < 0)
 				goto error;
-			ret = install_session_keyring(
-				context, context->user->session_keyring);
+			ret = install_session_keyring(t->user->session_keyring);
 			if (ret < 0)
 				goto error;
 		}
 
 		rcu_read_lock();
-		key = rcu_dereference(context->signal->session_keyring);
+		key = rcu_dereference(t->signal->session_keyring);
 		atomic_inc(&key->usage);
 		rcu_read_unlock();
 		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_USER_KEYRING:
-		if (!context->user->uid_keyring) {
-			ret = install_user_keyrings(context);
+		if (!t->user->uid_keyring) {
+			ret = install_user_keyrings();
 			if (ret < 0)
 				goto error;
 		}
 
-		key = context->user->uid_keyring;
+		key = t->user->uid_keyring;
 		atomic_inc(&key->usage);
 		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_USER_SESSION_KEYRING:
-		if (!context->user->session_keyring) {
-			ret = install_user_keyrings(context);
+		if (!t->user->session_keyring) {
+			ret = install_user_keyrings();
 			if (ret < 0)
 				goto error;
 		}
 
-		key = context->user->session_keyring;
+		key = t->user->session_keyring;
 		atomic_inc(&key->usage);
 		key_ref = make_key_ref(key, 1);
 		break;
@@ -669,7 +670,7 @@ key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
 		goto error;
 
 	case KEY_SPEC_REQKEY_AUTH_KEY:
-		key = context->request_key_auth;
+		key = t->request_key_auth;
 		if (!key)
 			goto error;
 
@@ -677,6 +678,25 @@ key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
 		key_ref = make_key_ref(key, 1);
 		break;
 
+	case KEY_SPEC_REQUESTOR_KEYRING:
+		if (!t->request_key_auth)
+			goto error;
+
+		down_read(&t->request_key_auth->sem);
+		if (t->request_key_auth->flags & KEY_FLAG_REVOKED) {
+			key_ref = ERR_PTR(-EKEYREVOKED);
+			key = NULL;
+		} else {
+			rka = t->request_key_auth->payload.data;
+			key = rka->dest_keyring;
+			atomic_inc(&key->usage);
+		}
+		up_read(&t->request_key_auth->sem);
+		if (!key)
+			goto error;
+		key_ref = make_key_ref(key, 1);
+		break;
+
 	default:
 		key_ref = ERR_PTR(-EINVAL);
 		if (id < 1)
@@ -725,7 +745,7 @@ key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
 		goto invalid_key;
 
 	/* check the permissions */
-	ret = key_task_permission(key_ref, context, perm);
+	ret = key_task_permission(key_ref, t, perm);
 	if (ret < 0)
 		goto invalid_key;
 
@@ -754,7 +774,7 @@ long join_session_keyring(const char *name)
 
 	/* if no name is provided, install an anonymous keyring */
 	if (!name) {
-		ret = install_session_keyring(tsk, NULL);
+		ret = install_session_keyring(NULL);
 		if (ret < 0)
 			goto error;
 
@@ -784,7 +804,7 @@ long join_session_keyring(const char *name)
 	}
 
 	/* we've got a keyring - now to install it */
-	ret = install_session_keyring(tsk, keyring);
+	ret = install_session_keyring(keyring);
 	if (ret < 0)
 		goto error2;