KEYS: Make request_key() and co fundamentally asynchronous

Make request_key() and co fundamentally asynchronous to make it easier for
NFS to make use of them.  There are now accessor functions that do
asynchronous constructions, a wait function to wait for construction to
complete, and a completion function for the key type to indicate completion
of construction.

Note that the construction queue is now gone.  Instead, keys under
construction are linked in to the appropriate keyring in advance, and that
anyone encountering one must wait for it to be complete before they can use
it.  This is done automatically for userspace.

The following auxiliary changes are also made:

 (1) Key type implementation stuff is split from linux/key.h into
     linux/key-type.h.

 (2) AF_RXRPC provides a way to allocate null rxrpc-type keys so that AFS does
     not need to call key_instantiate_and_link() directly.

 (3) Adjust the debugging macros so that they're -Wformat checked even if
     they are disabled, and make it so they can be enabled simply by defining
     __KDEBUG to be consistent with other code of mine.

 (3) Documentation.

[alan@lxorguk.ukuu.org.uk: keys: missing word in documentation]
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 271 insertions, 285 deletions

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 557500110a13..6381e616c477 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -1,6 +1,6 @@
-/* request_key.c: request a key from userspace
+/* Request a key from userspace
  *
- * Copyright (C) 2004-6 Red Hat, Inc. All Rights Reserved.
+ * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
  *
  * This program is free software; you can redistribute it and/or
@@ -18,27 +18,54 @@
 #include <linux/keyctl.h>
 #include "internal.h"
 
-struct key_construction {
-        struct list_head        link;   /* link in construction queue */
-        struct key              *key;   /* key being constructed */
-};
+/*
+ * wait_on_bit() sleep function for uninterruptible waiting
+ */
+static int key_wait_bit(void *flags)
+{
+        schedule();
+        return 0;
+}
+
+/*
+ * wait_on_bit() sleep function for interruptible waiting
+ */
+static int key_wait_bit_intr(void *flags)
+{
+        schedule();
+        return signal_pending(current) ? -ERESTARTSYS : 0;
+}
+
+/*
+ * call to complete the construction of a key
+ */
+void complete_request_key(struct key_construction *cons, int error)
+{
+        kenter("{%d,%d},%d", cons->key->serial, cons->authkey->serial, error);
 
-/* when waiting for someone else's keys, you get added to this */
-DECLARE_WAIT_QUEUE_HEAD(request_key_conswq);
+        if (error < 0)
+                key_negate_and_link(cons->key, key_negative_timeout, NULL,
+                                    cons->authkey);
+        else
+                key_revoke(cons->authkey);
+
+        key_put(cons->key);
+        key_put(cons->authkey);
+        kfree(cons);
+}
+EXPORT_SYMBOL(complete_request_key);
 
-/*****************************************************************************/
 /*
  * 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 *key,
-                                 struct key *authkey,
+static int call_sbin_request_key(struct key_construction *cons,
                                  const char *op,
                                  void *aux)
 {
         struct task_struct *tsk = current;
         key_serial_t prkey, sskey;
-        struct key *keyring;
+        struct key *key = cons->key, *authkey = cons->authkey, *keyring;
         char *argv[9], *envp[3], uid_str[12], gid_str[12];
         char key_str[12], keyring_str[3][12];
         char desc[20];
@@ -82,8 +109,7 @@ static int call_sbin_request_key(struct key *key,
                 rcu_read_lock();
                 sskey = rcu_dereference(tsk->signal->session_keyring)->serial;
                 rcu_read_unlock();
-        }
-        else {
+        } else {
                 sskey = tsk->user->session_keyring->serial;
         }
 
@@ -110,228 +136,77 @@ static int call_sbin_request_key(struct key *key,
         /* do it */
         ret = call_usermodehelper_keys(argv[0], argv, envp, keyring,
                                        UMH_WAIT_PROC);
+        kdebug("usermode -> 0x%x", ret);
+        if (ret >= 0) {
+                /* ret is the exit/wait code */
+                if (test_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags) ||
+                    key_validate(key) < 0)
+                        ret = -ENOKEY;
+                else
+                        /* ignore any errors from userspace if the key was
+                         * instantiated */
+                        ret = 0;
+        }
 
 error_link:
         key_put(keyring);
 
 error_alloc:
         kleave(" = %d", ret);
+        complete_request_key(cons, ret);
         return ret;
+}
 
-} /* end call_sbin_request_key() */
-
-/*****************************************************************************/
 /*
- * call out to userspace for the key
- * - called with the construction sem held, but the sem is dropped here
+ * call out to userspace for key construction
  * - we ignore program failure and go on key status instead
  */
-static struct key *__request_key_construction(struct key_type *type,
-                                              const char *description,
-                                              const char *callout_info,
-                                              void *aux,
-                                              unsigned long flags)
+static int construct_key(struct key *key, const char *callout_info, void *aux)
 {
+        struct key_construction *cons;
         request_key_actor_t actor;
-        struct key_construction cons;
-        struct timespec now;
-        struct key *key, *authkey;
-        int ret, negated;
+        struct key *authkey;
+        int ret;
 
-        kenter("%s,%s,%s,%lx", type->name, description, callout_info, flags);
+        kenter("%d,%s,%p", key->serial, callout_info, aux);
 
-        /* create a key and add it to the queue */
-        key = key_alloc(type, description,
-                        current->fsuid, current->fsgid, current, KEY_POS_ALL,
-                        flags);
-        if (IS_ERR(key))
-                goto alloc_failed;
-
-        set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
-
-        cons.key = key;
-        list_add_tail(&cons.link, &key->user->consq);
-
-        /* we drop the construction sem here on behalf of the caller */
-        up_write(&key_construction_sem);
+        cons = kmalloc(sizeof(*cons), GFP_KERNEL);
+        if (!cons)
+                return -ENOMEM;
 
         /* allocate an authorisation key */
         authkey = request_key_auth_new(key, callout_info);
         if (IS_ERR(authkey)) {
+                kfree(cons);
                 ret = PTR_ERR(authkey);
                 authkey = NULL;
-                goto alloc_authkey_failed;
-        }
-
-        /* make the call */
-        actor = call_sbin_request_key;
-        if (type->request_key)
-                actor = type->request_key;
-        ret = actor(key, authkey, "create", aux);
-        if (ret < 0)
-                goto request_failed;
-
-        /* if the key wasn't instantiated, then we want to give an error */
-        ret = -ENOKEY;
-        if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
-                goto request_failed;
-
-        key_revoke(authkey);
-        key_put(authkey);
-
-        down_write(&key_construction_sem);
-        list_del(&cons.link);
-        up_write(&key_construction_sem);
-
-        /* also give an error if the key was negatively instantiated */
-check_not_negative:
-        if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
-                key_put(key);
-                key = ERR_PTR(-ENOKEY);
-        }
-
-out:
-        kleave(" = %p", key);
-        return key;
-
-request_failed:
-        key_revoke(authkey);
-        key_put(authkey);
-
-alloc_authkey_failed:
-        /* it wasn't instantiated
-         * - remove from construction queue
-         * - mark the key as dead
-         */
-        negated = 0;
-        down_write(&key_construction_sem);
-
-        list_del(&cons.link);
-
-        /* check it didn't get instantiated between the check and the down */
-        if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
-                set_bit(KEY_FLAG_NEGATIVE, &key->flags);
-                set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
-                negated = 1;
-        }
-
-        clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
-
-        up_write(&key_construction_sem);
-
-        if (!negated)
-                goto check_not_negative; /* surprisingly, the key got
-                                          * instantiated */
-
-        /* set the timeout and store in the session keyring if we can */
-        now = current_kernel_time();
-        key->expiry = now.tv_sec + key_negative_timeout;
-
-        if (current->signal->session_keyring) {
-                struct key *keyring;
-
-                rcu_read_lock();
-                keyring = rcu_dereference(current->signal->session_keyring);
-                atomic_inc(&keyring->usage);
-                rcu_read_unlock();
-
-                key_link(keyring, key);
-                key_put(keyring);
-        }
-
-        key_put(key);
-
-        /* notify anyone who was waiting */
-        wake_up_all(&request_key_conswq);
-
-        key = ERR_PTR(ret);
-        goto out;
-
-alloc_failed:
-        up_write(&key_construction_sem);
-        goto out;
-
-} /* end __request_key_construction() */
-
-/*****************************************************************************/
-/*
- * call out to userspace to request the key
- * - we check the construction queue first to see if an appropriate key is
- *   already being constructed by userspace
- */
-static struct key *request_key_construction(struct key_type *type,
-                                            const char *description,
-                                            const char *callout_info,
-                                            void *aux,
-                                            struct key_user *user,
-                                            unsigned long flags)
-{
-        struct key_construction *pcons;
-        struct key *key, *ckey;
-
-        DECLARE_WAITQUEUE(myself, current);
-
-        kenter("%s,%s,{%d},%s,%lx",
-               type->name, description, user->uid, callout_info, flags);
-
-        /* see if there's such a key under construction already */
-        down_write(&key_construction_sem);
-
-        list_for_each_entry(pcons, &user->consq, link) {
-                ckey = pcons->key;
-
-                if (ckey->type != type)
-                        continue;
-
-                if (type->match(ckey, description))
-                        goto found_key_under_construction;
+        } else {
+                cons->authkey = key_get(authkey);
+                cons->key = key_get(key);
+
+                /* make the call */
+                actor = call_sbin_request_key;
+                if (key->type->request_key)
+                        actor = key->type->request_key;
+
+                ret = actor(cons, "create", 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);
         }
 
-        /* see about getting userspace to construct the key */
-        key = __request_key_construction(type, description, callout_info, aux,
-                                         flags);
- error:
-        kleave(" = %p", key);
-        return key;
-
-        /* someone else has the same key under construction
-         * - we want to keep an eye on their key
-         */
- found_key_under_construction:
-        atomic_inc(&ckey->usage);
-        up_write(&key_construction_sem);
-
-        /* wait for the key to be completed one way or another */
-        add_wait_queue(&request_key_conswq, &myself);
-
-        for (;;) {
-                set_current_state(TASK_INTERRUPTIBLE);
-                if (!test_bit(KEY_FLAG_USER_CONSTRUCT, &ckey->flags))
-                        break;
-                if (signal_pending(current))
-                        break;
-                schedule();
-        }
-
-        set_current_state(TASK_RUNNING);
-        remove_wait_queue(&request_key_conswq, &myself);
-
-        /* we'll need to search this process's keyrings to see if the key is
-         * now there since we can't automatically assume it's also available
-         * there */
-        key_put(ckey);
-        ckey = NULL;
-
-        key = NULL; /* request a retry */
-        goto error;
-
-} /* end request_key_construction() */
+        kleave(" = %d", ret);
+        return ret;
+}
 
-/*****************************************************************************/
 /*
- * link a freshly minted key to an appropriate destination keyring
+ * link a key to the appropriate destination keyring
+ * - the caller must hold a write lock on the destination keyring
  */
-static void request_key_link(struct key *key, struct key *dest_keyring)
+static void construct_key_make_link(struct key *key, struct key *dest_keyring)
 {
         struct task_struct *tsk = current;
         struct key *drop = NULL;
@@ -363,11 +238,11 @@ static void request_key_link(struct key *key, struct key *dest_keyring)
                                 break;
 
                 case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
-                        dest_keyring = current->user->session_keyring;
+                        dest_keyring = tsk->user->session_keyring;
                         break;
 
                 case KEY_REQKEY_DEFL_USER_KEYRING:
-                        dest_keyring = current->user->uid_keyring;
+                        dest_keyring = tsk->user->uid_keyring;
                         break;
 
                 case KEY_REQKEY_DEFL_GROUP_KEYRING:
@@ -377,15 +252,115 @@ static void request_key_link(struct key *key, struct key *dest_keyring)
         }
 
         /* and attach the key to it */
-        key_link(dest_keyring, key);
-
+        __key_link(dest_keyring, key);
         key_put(drop);
-
         kleave("");
+}
 
-} /* end request_key_link() */
+/*
+ * allocate a new key in under-construction state and attempt to link it in to
+ * the requested place
+ * - may return a key that's already under construction instead
+ */
+static int construct_alloc_key(struct key_type *type,
+                               const char *description,
+                               struct key *dest_keyring,
+                               unsigned long flags,
+                               struct key_user *user,
+                               struct key **_key)
+{
+        struct key *key;
+        key_ref_t key_ref;
+
+        kenter("%s,%s,,,", type->name, description);
+
+        mutex_lock(&user->cons_lock);
+
+        key = key_alloc(type, description,
+                        current->fsuid, current->fsgid, current, KEY_POS_ALL,
+                        flags);
+        if (IS_ERR(key))
+                goto alloc_failed;
+
+        set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
+
+        if (dest_keyring)
+                down_write(&dest_keyring->sem);
+
+        /* attach the key to the destination keyring under lock, but we do need
+         * to do another check just in case someone beat us to it whilst we
+         * waited for locks */
+        mutex_lock(&key_construction_mutex);
+
+        key_ref = search_process_keyrings(type, description, type->match,
+                                          current);
+        if (!IS_ERR(key_ref))
+                goto key_already_present;
+
+        if (dest_keyring)
+                construct_key_make_link(key, dest_keyring);
+
+        mutex_unlock(&key_construction_mutex);
+        if (dest_keyring)
+                up_write(&dest_keyring->sem);
+        mutex_unlock(&user->cons_lock);
+        *_key = key;
+        kleave(" = 0 [%d]", key_serial(key));
+        return 0;
+
+key_already_present:
+        mutex_unlock(&key_construction_mutex);
+        if (dest_keyring)
+                up_write(&dest_keyring->sem);
+        mutex_unlock(&user->cons_lock);
+        key_put(key);
+        *_key = key = key_ref_to_ptr(key_ref);
+        kleave(" = -EINPROGRESS [%d]", key_serial(key));
+        return -EINPROGRESS;
+
+alloc_failed:
+        mutex_unlock(&user->cons_lock);
+        *_key = NULL;
+        kleave(" = %ld", PTR_ERR(key));
+        return PTR_ERR(key);
+}
+
+/*
+ * commence key construction
+ */
+static struct key *construct_key_and_link(struct key_type *type,
+                                          const char *description,
+                                          const char *callout_info,
+                                          void *aux,
+                                          struct key *dest_keyring,
+                                          unsigned long flags)
+{
+        struct key_user *user;
+        struct key *key;
+        int ret;
+
+        user = key_user_lookup(current->fsuid);
+        if (!user)
+                return ERR_PTR(-ENOMEM);
+
+        ret = construct_alloc_key(type, description, dest_keyring, flags, user,
+                                  &key);
+        key_user_put(user);
+
+        if (ret == 0) {
+                ret = construct_key(key, callout_info, aux);
+                if (ret < 0)
+                        goto construction_failed;
+        }
+
+        return key;
+
+construction_failed:
+        key_negate_and_link(key, key_negative_timeout, NULL, NULL);
+        key_put(key);
+        return ERR_PTR(ret);
+}
 
-/*****************************************************************************/
 /*
  * request a key
  * - search the process's keyrings
@@ -400,7 +375,6 @@ struct key *request_key_and_link(struct key_type *type,
                                  struct key *dest_keyring,
                                  unsigned long flags)
 {
-        struct key_user *user;
         struct key *key;
         key_ref_t key_ref;
 
@@ -412,112 +386,124 @@ struct key *request_key_and_link(struct key_type *type,
         key_ref = search_process_keyrings(type, description, type->match,
                                           current);
 
-        kdebug("search 1: %p", key_ref);
-
         if (!IS_ERR(key_ref)) {
                 key = key_ref_to_ptr(key_ref);
-        }
-        else if (PTR_ERR(key_ref) != -EAGAIN) {
+        } else if (PTR_ERR(key_ref) != -EAGAIN) {
                 key = ERR_PTR(PTR_ERR(key_ref));
-        }
-        else  {
+        } else  {
                 /* the search failed, but the keyrings were searchable, so we
                  * should consult userspace if we can */
                 key = ERR_PTR(-ENOKEY);
                 if (!callout_info)
                         goto error;
 
-                /* - get hold of the user's construction queue */
-                user = key_user_lookup(current->fsuid);
-                if (!user)
-                        goto nomem;
-
-                for (;;) {
-                        if (signal_pending(current))
-                                goto interrupted;
-
-                        /* ask userspace (returns NULL if it waited on a key
-                         * being constructed) */
-                        key = request_key_construction(type, description,
-                                                       callout_info, aux,
-                                                       user, flags);
-                        if (key)
-                                break;
-
-                        /* someone else made the key we want, so we need to
-                         * search again as it might now be available to us */
-                        key_ref = search_process_keyrings(type, description,
-                                                          type->match,
-                                                          current);
-
-                        kdebug("search 2: %p", key_ref);
-
-                        if (!IS_ERR(key_ref)) {
-                                key = key_ref_to_ptr(key_ref);
-                                break;
-                        }
-
-                        if (PTR_ERR(key_ref) != -EAGAIN) {
-                                key = ERR_PTR(PTR_ERR(key_ref));
-                                break;
-                        }
-                }
-
-                key_user_put(user);
-
-                /* link the new key into the appropriate keyring */
-                if (!IS_ERR(key))
-                        request_key_link(key, dest_keyring);
+                key = construct_key_and_link(type, description, callout_info,
+                                             aux, dest_keyring, flags);
         }
 
 error:
         kleave(" = %p", key);
         return key;
+}
 
-nomem:
-        key = ERR_PTR(-ENOMEM);
-        goto error;
-
-interrupted:
-        key_user_put(user);
-        key = ERR_PTR(-EINTR);
-        goto error;
+/*
+ * wait for construction of a key to complete
+ */
+int wait_for_key_construction(struct key *key, bool intr)
+{
+        int ret;
 
-} /* end request_key_and_link() */
+        ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
+                          intr ? key_wait_bit_intr : key_wait_bit,
+                          intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
+        if (ret < 0)
+                return ret;
+        return key_validate(key);
+}
+EXPORT_SYMBOL(wait_for_key_construction);
 
-/*****************************************************************************/
 /*
  * request a key
  * - search the process's keyrings
  * - check the list of keys being created or updated
  * - call out to userspace for a key if supplementary info was provided
+ * - waits uninterruptible for creation to complete
  */
 struct key *request_key(struct key_type *type,
                         const char *description,
                         const char *callout_info)
 {
-        return request_key_and_link(type, description, callout_info, NULL,
-                                    NULL, KEY_ALLOC_IN_QUOTA);
-
-} /* end request_key() */
-
+        struct key *key;
+        int ret;
+
+        key = request_key_and_link(type, description, callout_info, NULL,
+                                   NULL, KEY_ALLOC_IN_QUOTA);
+        if (!IS_ERR(key)) {
+                ret = wait_for_key_construction(key, false);
+                if (ret < 0) {
+                        key_put(key);
+                        return ERR_PTR(ret);
+                }
+        }
+        return key;
+}
 EXPORT_SYMBOL(request_key);
 
-/*****************************************************************************/
 /*
  * request a key with auxiliary data for the upcaller
  * - search the process's keyrings
  * - check the list of keys being created or updated
  * - call out to userspace for a key if supplementary info was provided
+ * - waits uninterruptible for creation to complete
  */
 struct key *request_key_with_auxdata(struct key_type *type,
                                      const char *description,
                                      const char *callout_info,
                                      void *aux)
 {
-        return request_key_and_link(type, description, callout_info, aux,
-                                    NULL, KEY_ALLOC_IN_QUOTA);
+        struct key *key;
+        int ret;
+
+        key = request_key_and_link(type, description, callout_info, aux,
+                                   NULL, KEY_ALLOC_IN_QUOTA);
+        if (!IS_ERR(key)) {
+                ret = wait_for_key_construction(key, false);
+                if (ret < 0) {
+                        key_put(key);
+                        return ERR_PTR(ret);
+                }
+        }
+        return key;
+}
+EXPORT_SYMBOL(request_key_with_auxdata);
 
-} /* end request_key_with_auxdata() */
+/*
+ * request a key (allow async construction)
+ * - search the process's keyrings
+ * - check the list of keys being created or updated
+ * - call out to userspace for a key if supplementary info was provided
+ */
+struct key *request_key_async(struct key_type *type,
+                              const char *description,
+                              const char *callout_info)
+{
+        return request_key_and_link(type, description, callout_info, NULL,
+                                    NULL, KEY_ALLOC_IN_QUOTA);
+}
+EXPORT_SYMBOL(request_key_async);
 
-EXPORT_SYMBOL(request_key_with_auxdata);
+/*
+ * request a key with auxiliary data for the upcaller (allow async construction)
+ * - search the process's keyrings
+ * - check the list of keys being created or updated
+ * - call out to userspace for a key if supplementary info was provided
+ */
+struct key *request_key_async_with_auxdata(struct key_type *type,
+                                           const char *description,
+                                           const char *callout_info,
+                                           void *aux)
+{
+        return request_key_and_link(type, description, callout_info, aux,
+                                    NULL, KEY_ALLOC_IN_QUOTA);
+}
+EXPORT_SYMBOL(request_key_async_with_auxdata);