Merge tag 'keys-misc-20190619' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull misc keyring updates from David Howells:
 "These are some miscellaneous keyrings fixes and improvements:

   - Fix a bunch of warnings from sparse, including missing RCU bits and
     kdoc-function argument mismatches

   - Implement a keyctl to allow a key to be moved from one keyring to
     another, with the option of prohibiting key replacement in the
     destination keyring.

   - Grant Link permission to possessors of request_key_auth tokens so
     that upcall servicing daemons can more easily arrange things such
     that only the necessary auth key is passed to the actual service
     program, and not all the auth keys a daemon might possesss.

   - Improvement in lookup_user_key().

   - Implement a keyctl to allow keyrings subsystem capabilities to be
     queried.

  The keyutils next branch has commits to make available, document and
  test the move-key and capabilities code:

        https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/log

  They're currently on the 'next' branch"

* tag 'keys-misc-20190619' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys: Add capability-checking keyctl function
  keys: Reuse keyring_index_key::desc_len in lookup_user_key()
  keys: Grant Link permission to possessers of request_key auth keys
  keys: Add a keyctl to move a key between keyrings
  keys: Hoist locking out of __key_link_begin()
  keys: Break bits out of key_unlink()
  keys: Change keyring_serialise_link_sem to a mutex
  keys: sparse: Fix kdoc mismatches
  keys: sparse: Fix incorrect RCU accesses
  keys: sparse: Fix key_fs[ug]id_changed()

1 files changed, 226 insertions, 52 deletions

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index e311cc5df358..204b5a4d180e 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -96,7 +96,7 @@ EXPORT_SYMBOL(key_type_keyring);
  * Semaphore to serialise link/link calls to prevent two link calls in parallel
  * introducing a cycle.
  */
-static DECLARE_RWSEM(keyring_serialise_link_sem);
+static DEFINE_MUTEX(keyring_serialise_link_lock);
 
 /*
  * Publish the name of a keyring so that it can be found by name (if it has
@@ -516,7 +516,7 @@ EXPORT_SYMBOL(keyring_alloc);
  * @keyring: The keyring being added to.
  * @type: The type of key being added.
  * @payload: The payload of the key intended to be added.
- * @data: Additional data for evaluating restriction.
+ * @restriction_key: Keys providing additional data for evaluating restriction.
  *
  * Reject the addition of any links to a keyring.  It can be overridden by
  * passing KEY_ALLOC_BYPASS_RESTRICTION to key_instantiate_and_link() when
@@ -972,9 +972,13 @@ static bool keyring_detect_restriction_cycle(const struct key *dest_keyring,
 
 /**
  * keyring_restrict - Look up and apply a restriction to a keyring
- *
- * @keyring: The keyring to be restricted
+ * @keyring_ref: The keyring to be restricted
+ * @type: The key type that will provide the restriction checker.
  * @restriction: The restriction options to apply to the keyring
+ *
+ * Look up a keyring and apply a restriction to it.  The restriction is managed
+ * by the specific key type, but can be configured by the options specified in
+ * the restriction string.
  */
 int keyring_restrict(key_ref_t keyring_ref, const char *type,
 		     const char *restriction)
@@ -1192,13 +1196,67 @@ static int keyring_detect_cycle(struct key *A, struct key *B)
 }
 
 /*
+ * Lock keyring for link.
+ */
+int __key_link_lock(struct key *keyring,
+		    const struct keyring_index_key *index_key)
+	__acquires(&keyring->sem)
+	__acquires(&keyring_serialise_link_lock)
+{
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	down_write(&keyring->sem);
+
+	/* Serialise link/link calls to prevent parallel calls causing a cycle
+	 * when linking two keyring in opposite orders.
+	 */
+	if (index_key->type == &key_type_keyring)
+		mutex_lock(&keyring_serialise_link_lock);
+
+	return 0;
+}
+
+/*
+ * Lock keyrings for move (link/unlink combination).
+ */
+int __key_move_lock(struct key *l_keyring, struct key *u_keyring,
+		    const struct keyring_index_key *index_key)
+	__acquires(&l_keyring->sem)
+	__acquires(&u_keyring->sem)
+	__acquires(&keyring_serialise_link_lock)
+{
+	if (l_keyring->type != &key_type_keyring ||
+	    u_keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	/* We have to be very careful here to take the keyring locks in the
+	 * right order, lest we open ourselves to deadlocking against another
+	 * move operation.
+	 */
+	if (l_keyring < u_keyring) {
+		down_write(&l_keyring->sem);
+		down_write_nested(&u_keyring->sem, 1);
+	} else {
+		down_write(&u_keyring->sem);
+		down_write_nested(&l_keyring->sem, 1);
+	}
+
+	/* Serialise link/link calls to prevent parallel calls causing a cycle
+	 * when linking two keyring in opposite orders.
+	 */
+	if (index_key->type == &key_type_keyring)
+		mutex_lock(&keyring_serialise_link_lock);
+
+	return 0;
+}
+
+/*
  * Preallocate memory so that a key can be linked into to a keyring.
  */
 int __key_link_begin(struct key *keyring,
 		     const struct keyring_index_key *index_key,
 		     struct assoc_array_edit **_edit)
-	__acquires(&keyring->sem)
-	__acquires(&keyring_serialise_link_sem)
 {
 	struct assoc_array_edit *edit;
 	int ret;
@@ -1207,20 +1265,13 @@ int __key_link_begin(struct key *keyring,
 	       keyring->serial, index_key->type->name, index_key->description);
 
 	BUG_ON(index_key->desc_len == 0);
+	BUG_ON(*_edit != NULL);
 
-	if (keyring->type != &key_type_keyring)
-		return -ENOTDIR;
-
-	down_write(&keyring->sem);
+	*_edit = NULL;
 
 	ret = -EKEYREVOKED;
 	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
-		goto error_krsem;
-
-	/* serialise link/link calls to prevent parallel calls causing a cycle
-	 * when linking two keyring in opposite orders */
-	if (index_key->type == &key_type_keyring)
-		down_write(&keyring_serialise_link_sem);
+		goto error;
 
 	/* Create an edit script that will insert/replace the key in the
 	 * keyring tree.
@@ -1231,7 +1282,7 @@ int __key_link_begin(struct key *keyring,
 				  NULL);
 	if (IS_ERR(edit)) {
 		ret = PTR_ERR(edit);
-		goto error_sem;
+		goto error;
 	}
 
 	/* If we're not replacing a link in-place then we're going to need some
@@ -1250,11 +1301,7 @@ int __key_link_begin(struct key *keyring,
 
 error_cancel:
 	assoc_array_cancel_edit(edit);
-error_sem:
-	if (index_key->type == &key_type_keyring)
-		up_write(&keyring_serialise_link_sem);
-error_krsem:
-	up_write(&keyring->sem);
+error:
 	kleave(" = %d", ret);
 	return ret;
 }
@@ -1299,14 +1346,11 @@ void __key_link_end(struct key *keyring,
 		    const struct keyring_index_key *index_key,
 		    struct assoc_array_edit *edit)
 	__releases(&keyring->sem)
-	__releases(&keyring_serialise_link_sem)
+	__releases(&keyring_serialise_link_lock)
 {
 	BUG_ON(index_key->type == NULL);
 	kenter("%d,%s,", keyring->serial, index_key->type->name);
 
-	if (index_key->type == &key_type_keyring)
-		up_write(&keyring_serialise_link_sem);
-
 	if (edit) {
 		if (!edit->dead_leaf) {
 			key_payload_reserve(keyring,
@@ -1315,6 +1359,9 @@ void __key_link_end(struct key *keyring,
 		assoc_array_cancel_edit(edit);
 	}
 	up_write(&keyring->sem);
+
+	if (index_key->type == &key_type_keyring)
+		mutex_unlock(&keyring_serialise_link_lock);
 }
 
 /*
@@ -1350,7 +1397,7 @@ static int __key_link_check_restriction(struct key *keyring, struct key *key)
  */
 int key_link(struct key *keyring, struct key *key)
 {
-	struct assoc_array_edit *edit;
+	struct assoc_array_edit *edit = NULL;
 	int ret;
 
 	kenter("{%d,%d}", keyring->serial, refcount_read(&keyring->usage));
@@ -1358,22 +1405,88 @@ int key_link(struct key *keyring, struct key *key)
 	key_check(keyring);
 	key_check(key);
 
+	ret = __key_link_lock(keyring, &key->index_key);
+	if (ret < 0)
+		goto error;
+
 	ret = __key_link_begin(keyring, &key->index_key, &edit);
-	if (ret == 0) {
-		kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
-		ret = __key_link_check_restriction(keyring, key);
-		if (ret == 0)
-			ret = __key_link_check_live_key(keyring, key);
-		if (ret == 0)
-			__key_link(key, &edit);
-		__key_link_end(keyring, &key->index_key, edit);
-	}
+	if (ret < 0)
+		goto error_end;
+
+	kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
+	ret = __key_link_check_restriction(keyring, key);
+	if (ret == 0)
+		ret = __key_link_check_live_key(keyring, key);
+	if (ret == 0)
+		__key_link(key, &edit);
 
+error_end:
+	__key_link_end(keyring, &key->index_key, edit);
+error:
 	kleave(" = %d {%d,%d}", ret, keyring->serial, refcount_read(&keyring->usage));
 	return ret;
 }
 EXPORT_SYMBOL(key_link);
 
+/*
+ * Lock a keyring for unlink.
+ */
+static int __key_unlink_lock(struct key *keyring)
+	__acquires(&keyring->sem)
+{
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	down_write(&keyring->sem);
+	return 0;
+}
+
+/*
+ * Begin the process of unlinking a key from a keyring.
+ */
+static int __key_unlink_begin(struct key *keyring, struct key *key,
+			      struct assoc_array_edit **_edit)
+{
+	struct assoc_array_edit *edit;
+
+	BUG_ON(*_edit != NULL);
+	
+	edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
+				  &key->index_key);
+	if (IS_ERR(edit))
+		return PTR_ERR(edit);
+
+	if (!edit)
+		return -ENOENT;
+
+	*_edit = edit;
+	return 0;
+}
+
+/*
+ * Apply an unlink change.
+ */
+static void __key_unlink(struct key *keyring, struct key *key,
+			 struct assoc_array_edit **_edit)
+{
+	assoc_array_apply_edit(*_edit);
+	*_edit = NULL;
+	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
+}
+
+/*
+ * Finish unlinking a key from to a keyring.
+ */
+static void __key_unlink_end(struct key *keyring,
+			     struct key *key,
+			     struct assoc_array_edit *edit)
+	__releases(&keyring->sem)
+{
+	if (edit)
+		assoc_array_cancel_edit(edit);
+	up_write(&keyring->sem);
+}
+
 /**
  * key_unlink - Unlink the first link to a key from a keyring.
  * @keyring: The keyring to remove the link from.
@@ -1393,36 +1506,97 @@ EXPORT_SYMBOL(key_link);
  */
 int key_unlink(struct key *keyring, struct key *key)
 {
-	struct assoc_array_edit *edit;
+	struct assoc_array_edit *edit = NULL;
 	int ret;
 
 	key_check(keyring);
 	key_check(key);
 
-	if (keyring->type != &key_type_keyring)
-		return -ENOTDIR;
+	ret = __key_unlink_lock(keyring);
+	if (ret < 0)
+		return ret;
 
-	down_write(&keyring->sem);
+	ret = __key_unlink_begin(keyring, key, &edit);
+	if (ret == 0)
+		__key_unlink(keyring, key, &edit);
+	__key_unlink_end(keyring, key, edit);
+	return ret;
+}
+EXPORT_SYMBOL(key_unlink);
 
-	edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
-				  &key->index_key);
-	if (IS_ERR(edit)) {
-		ret = PTR_ERR(edit);
+/**
+ * key_move - Move a key from one keyring to another
+ * @key: The key to move
+ * @from_keyring: The keyring to remove the link from.
+ * @to_keyring: The keyring to make the link in.
+ * @flags: Qualifying flags, such as KEYCTL_MOVE_EXCL.
+ *
+ * Make a link in @to_keyring to a key, such that the keyring holds a reference
+ * on that key and the key can potentially be found by searching that keyring
+ * whilst simultaneously removing a link to the key from @from_keyring.
+ *
+ * This function will write-lock both keyring's semaphores and will consume
+ * some of the user's key data quota to hold the link on @to_keyring.
+ *
+ * Returns 0 if successful, -ENOTDIR if either keyring isn't a keyring,
+ * -EKEYREVOKED if either keyring has been revoked, -ENFILE if the second
+ * keyring is full, -EDQUOT if there is insufficient key data quota remaining
+ * to add another link or -ENOMEM if there's insufficient memory.  If
+ * KEYCTL_MOVE_EXCL is set, then -EEXIST will be returned if there's already a
+ * matching key in @to_keyring.
+ *
+ * It is assumed that the caller has checked that it is permitted for a link to
+ * be made (the keyring should have Write permission and the key Link
+ * permission).
+ */
+int key_move(struct key *key,
+	     struct key *from_keyring,
+	     struct key *to_keyring,
+	     unsigned int flags)
+{
+	struct assoc_array_edit *from_edit = NULL, *to_edit = NULL;
+	int ret;
+
+	kenter("%d,%d,%d", key->serial, from_keyring->serial, to_keyring->serial);
+
+	if (from_keyring == to_keyring)
+		return 0;
+
+	key_check(key);
+	key_check(from_keyring);
+	key_check(to_keyring);
+
+	ret = __key_move_lock(from_keyring, to_keyring, &key->index_key);
+	if (ret < 0)
+		goto out;
+	ret = __key_unlink_begin(from_keyring, key, &from_edit);
+	if (ret < 0)
 		goto error;
-	}
-	ret = -ENOENT;
-	if (edit == NULL)
+	ret = __key_link_begin(to_keyring, &key->index_key, &to_edit);
+	if (ret < 0)
 		goto error;
 
-	assoc_array_apply_edit(edit);
-	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
-	ret = 0;
+	ret = -EEXIST;
+	if (to_edit->dead_leaf && (flags & KEYCTL_MOVE_EXCL))
+		goto error;
 
+	ret = __key_link_check_restriction(to_keyring, key);
+	if (ret < 0)
+		goto error;
+	ret = __key_link_check_live_key(to_keyring, key);
+	if (ret < 0)
+		goto error;
+
+	__key_unlink(from_keyring, key, &from_edit);
+	__key_link(key, &to_edit);
 error:
-	up_write(&keyring->sem);
+	__key_link_end(to_keyring, &key->index_key, to_edit);
+	__key_unlink_end(from_keyring, key, from_edit);
+out:
+	kleave(" = %d", ret);
 	return ret;
 }
-EXPORT_SYMBOL(key_unlink);
+EXPORT_SYMBOL(key_move);
 
 /**
  * keyring_clear - Clear a keyring