keys: Fix dependency loop between construction record and auth key

In the request_key() upcall mechanism there's a dependency loop by which if
a key type driver overrides the ->request_key hook and the userspace side
manages to lose the authorisation key, the auth key and the internal
construction record (struct key_construction) can keep each other pinned.

Fix this by the following changes:

 (1) Killing off the construction record and using the auth key instead.

 (2) Including the operation name in the auth key payload and making the
     payload available outside of security/keys/.

 (3) The ->request_key hook is given the authkey instead of the cons
     record and operation name.

Changes (2) and (3) allow the auth key to naturally be cleaned up if the
keyring it is in is destroyed or cleared or the auth key is unlinked.

Fixes: 7ee02a316600 ("keys: Fix dependency loop between construction record and auth key")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.morris@microsoft.com>

5 files changed, 41 insertions, 62 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 479909b858c7..8f533c81aa8d 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -186,20 +186,9 @@ static inline int key_permission(const key_ref_t key_ref, unsigned perm)
 	return key_task_permission(key_ref, current_cred(), perm);
 }
 
-/*
- * Authorisation record for request_key().
- */
-struct request_key_auth {
-	struct key		*target_key;
-	struct key		*dest_keyring;
-	const struct cred	*cred;
-	void			*callout_info;
-	size_t			callout_len;
-	pid_t			pid;
-} __randomize_layout;
-
 extern struct key_type key_type_request_key_auth;
 extern struct key *request_key_auth_new(struct key *target,
+					const char *op,
 					const void *callout_info,
 					size_t callout_len,
 					struct key *dest_keyring);
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index e8093d025966..7bbe03593e58 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -25,6 +25,7 @@
 #include <linux/security.h>
 #include <linux/uio.h>
 #include <linux/uaccess.h>
+#include <keys/request_key_auth-type.h>
 #include "internal.h"
 
 #define KEY_MAX_DESC_SIZE 4096
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 02c77e928f68..0e0b9ccad2f8 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -19,6 +19,7 @@
 #include <linux/security.h>
 #include <linux/user_namespace.h>
 #include <linux/uaccess.h>
+#include <keys/request_key_auth-type.h>
 #include "internal.h"
 
 /* Session keyring create vs join semaphore */
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 301f0e300dbd..3f56a312dd35 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -18,31 +18,30 @@
 #include <linux/keyctl.h>
 #include <linux/slab.h>
 #include "internal.h"
+#include <keys/request_key_auth-type.h>
 
 #define key_negative_timeout	60	/* default timeout on a negative key's existence */
 
 /**
  * complete_request_key - Complete the construction of a key.
- * @cons: The key construction record.
+ * @auth_key: The authorisation key.
  * @error: The success or failute of the construction.
  *
  * Complete the attempt to construct a key.  The key will be negated
  * if an error is indicated.  The authorisation key will be revoked
  * unconditionally.
  */
-void complete_request_key(struct key_construction *cons, int error)
+void complete_request_key(struct key *authkey, int error)
 {
-	kenter("{%d,%d},%d", cons->key->serial, cons->authkey->serial, error);
+	struct request_key_auth *rka = get_request_key_auth(authkey);
+	struct key *key = rka->target_key;
+
+	kenter("%d{%d},%d", authkey->serial, key->serial, error);
 
 	if (error < 0)
-		key_negate_and_link(cons->key, key_negative_timeout, NULL,
-				    cons->authkey);
+		key_negate_and_link(key, key_negative_timeout, NULL, authkey);
 	else
-		key_revoke(cons->authkey);
-
-	key_put(cons->key);
-	key_put(cons->authkey);
-	kfree(cons);
+		key_revoke(authkey);
 }
 EXPORT_SYMBOL(complete_request_key);
 
@@ -91,21 +90,19 @@ static int call_usermodehelper_keys(const char *path, char **argv, char **envp,
  * Request userspace finish the construction of a key
  * - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring>"
  */
-static int call_sbin_request_key(struct key_construction *cons,
-				 const char *op,
-				 void *aux)
+static int call_sbin_request_key(struct key *authkey, void *aux)
 {
 	static char const request_key[] = "/sbin/request-key";
+	struct request_key_auth *rka = get_request_key_auth(authkey);
 	const struct cred *cred = current_cred();
 	key_serial_t prkey, sskey;
-	struct key *key = cons->key, *authkey = cons->authkey, *keyring,
-		*session;
+	struct key *key = rka->target_key, *keyring, *session;
 	char *argv[9], *envp[3], uid_str[12], gid_str[12];
 	char key_str[12], keyring_str[3][12];
 	char desc[20];
 	int ret, i;
 
-	kenter("{%d},{%d},%s", key->serial, authkey->serial, op);
+	kenter("{%d},{%d},%s", key->serial, authkey->serial, rka->op);
 
 	ret = install_user_keyrings();
 	if (ret < 0)
@@ -163,7 +160,7 @@ static int call_sbin_request_key(struct key_construction *cons,
 	/* set up the argument list */
 	i = 0;
 	argv[i++] = (char *)request_key;
-	argv[i++] = (char *) op;
+	argv[i++] = (char *)rka->op;
 	argv[i++] = key_str;
 	argv[i++] = uid_str;
 	argv[i++] = gid_str;
@@ -191,7 +188,7 @@ error_link:
 	key_put(keyring);
 
 error_alloc:
-	complete_request_key(cons, ret);
+	complete_request_key(authkey, ret);
 	kleave(" = %d", ret);
 	return ret;
 }
@@ -205,42 +202,31 @@ static int construct_key(struct key *key, const void *callout_info,
 			 size_t callout_len, void *aux,
 			 struct key *dest_keyring)
 {
-	struct key_construction *cons;
 	request_key_actor_t actor;
 	struct key *authkey;
 	int ret;
 
 	kenter("%d,%p,%zu,%p", key->serial, callout_info, callout_len, aux);
 
-	cons = kmalloc(sizeof(*cons), GFP_KERNEL);
-	if (!cons)
-		return -ENOMEM;
-
 	/* allocate an authorisation key */
-	authkey = request_key_auth_new(key, callout_info, callout_len,
+	authkey = request_key_auth_new(key, "create", callout_info, callout_len,
 				       dest_keyring);
-	if (IS_ERR(authkey)) {
-		kfree(cons);
-		ret = PTR_ERR(authkey);
-		authkey = NULL;
-	} else {
-		cons->authkey = key_get(authkey);
-		cons->key = key_get(key);
+	if (IS_ERR(authkey))
+		return PTR_ERR(authkey);
 
-		/* make the call */
-		actor = call_sbin_request_key;
-		if (key->type->request_key)
-			actor = key->type->request_key;
+	/* Make the call */
+	actor = call_sbin_request_key;
+	if (key->type->request_key)
+		actor = key->type->request_key;
 
-		ret = actor(cons, "create", aux);
+	ret = actor(authkey, aux);
 
-		/* check that the actor called complete_request_key() prior to
-		 * returning an error */
-		WARN_ON(ret < 0 &&
-			!test_bit(KEY_FLAG_REVOKED, &authkey->flags));
-		key_put(authkey);
-	}
+	/* check that the actor called complete_request_key() prior to
+	 * returning an error */
+	WARN_ON(ret < 0 &&
+		!test_bit(KEY_FLAG_REVOKED, &authkey->flags));
 
+	key_put(authkey);
 	kleave(" = %d", ret);
 	return ret;
 }
@@ -275,7 +261,7 @@ static int construct_get_dest_keyring(struct key **_dest_keyring)
 			if (cred->request_key_auth) {
 				authkey = cred->request_key_auth;
 				down_read(&authkey->sem);
-				rka = authkey->payload.data[0];
+				rka = get_request_key_auth(authkey);
 				if (!test_bit(KEY_FLAG_REVOKED,
 					      &authkey->flags))
 					dest_keyring =
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 87ea2f54dedc..afc304e8b61e 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -17,7 +17,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include "internal.h"
-#include <keys/user-type.h>
+#include <keys/request_key_auth-type.h>
 
 static int request_key_auth_preparse(struct key_preparsed_payload *);
 static void request_key_auth_free_preparse(struct key_preparsed_payload *);
@@ -68,7 +68,7 @@ static int request_key_auth_instantiate(struct key *key,
 static void request_key_auth_describe(const struct key *key,
 				      struct seq_file *m)
 {
-	struct request_key_auth *rka = key->payload.data[0];
+	struct request_key_auth *rka = get_request_key_auth(key);
 
 	seq_puts(m, "key:");
 	seq_puts(m, key->description);
@@ -83,7 +83,7 @@ static void request_key_auth_describe(const struct key *key,
 static long request_key_auth_read(const struct key *key,
 				  char __user *buffer, size_t buflen)
 {
-	struct request_key_auth *rka = key->payload.data[0];
+	struct request_key_auth *rka = get_request_key_auth(key);
 	size_t datalen;
 	long ret;
 
@@ -109,7 +109,7 @@ static long request_key_auth_read(const struct key *key,
  */
 static void request_key_auth_revoke(struct key *key)
 {
-	struct request_key_auth *rka = key->payload.data[0];
+	struct request_key_auth *rka = get_request_key_auth(key);
 
 	kenter("{%d}", key->serial);
 
@@ -136,7 +136,7 @@ static void free_request_key_auth(struct request_key_auth *rka)
  */
 static void request_key_auth_destroy(struct key *key)
 {
-	struct request_key_auth *rka = key->payload.data[0];
+	struct request_key_auth *rka = get_request_key_auth(key);
 
 	kenter("{%d}", key->serial);
 
@@ -147,8 +147,9 @@ static void request_key_auth_destroy(struct key *key)
  * Create an authorisation token for /sbin/request-key or whoever to gain
  * access to the caller's security data.
  */
-struct key *request_key_auth_new(struct key *target, const void *callout_info,
-				 size_t callout_len, struct key *dest_keyring)
+struct key *request_key_auth_new(struct key *target, const char *op,
+				 const void *callout_info, size_t callout_len,
+				 struct key *dest_keyring)
 {
 	struct request_key_auth *rka, *irka;
 	const struct cred *cred = current->cred;
@@ -166,6 +167,7 @@ struct key *request_key_auth_new(struct key *target, const void *callout_info,
 	if (!rka->callout_info)
 		goto error_free_rka;
 	rka->callout_len = callout_len;
+	strlcpy(rka->op, op, sizeof(rka->op));
 
 	/* see if the calling process is already servicing the key request of
 	 * another process */