security/keys/request_key.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /* Request a key from userspace
  *
  * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
  *
  * See Documentation/security/keys/request-key.rst
  */

 #include <linux/export.h>
 #include <linux/sched.h>
 #include <linux/kmod.h>
 #include <linux/err.h>
 #include <linux/keyctl.h>
 #include <linux/slab.h>
 #include <net/net_namespace.h>
 #include "internal.h"
 #include <keys/request_key_auth-type.h>

 #define key_negative_timeout	60	/* default timeout on a negative key's existence */

 static struct key *check_cached_key(struct keyring_search_context *ctx)
 {
 #ifdef CONFIG_KEYS_REQUEST_CACHE
 	struct key *key = current->cached_requested_key;

 	if (key &&
 	    ctx->match_data.cmp(key, &ctx->match_data) &&
 	    !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
 			    (1 << KEY_FLAG_REVOKED))))
 		return key_get(key);
 #endif
 	return NULL;
 }

 static void cache_requested_key(struct key *key)
 {
 #ifdef CONFIG_KEYS_REQUEST_CACHE
 	struct task_struct *t = current;

 	key_put(t->cached_requested_key);
 	t->cached_requested_key = key_get(key);
 	set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
 #endif
 }

 /**
  * complete_request_key - Complete the construction of a key.
  * @authkey: 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 *authkey, int 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(key, key_negative_timeout, NULL, authkey);
 	else
 		key_revoke(authkey);
 }
 EXPORT_SYMBOL(complete_request_key);

 /*
  * Initialise a usermode helper that is going to have a specific session
  * keyring.
  *
  * This is called in context of freshly forked kthread before kernel_execve(),
  * so we can simply install the desired session_keyring at this point.
  */
 static int umh_keys_init(struct subprocess_info *info, struct cred *cred)
 {
 	struct key *keyring = info->data;

 	return install_session_keyring_to_cred(cred, keyring);
 }

 /*
  * Clean up a usermode helper with session keyring.
  */
 static void umh_keys_cleanup(struct subprocess_info *info)
 {
 	struct key *keyring = info->data;
 	key_put(keyring);
 }

 /*
  * Call a usermode helper with a specific session keyring.
  */
 static int call_usermodehelper_keys(const char *path, char **argv, char **envp,
 					struct key *session_keyring, int wait)
 {
 	struct subprocess_info *info;

 	info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL,
 					  umh_keys_init, umh_keys_cleanup,
 					  session_keyring);
 	if (!info)
 		return -ENOMEM;

 	key_get(session_keyring);
 	return call_usermodehelper_exec(info, wait);
 }

 /*
  * 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 *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 = rka->target_key, *keyring, *session, *user_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, rka->op);

 	ret = look_up_user_keyrings(NULL, &user_session);
 	if (ret < 0)
 		goto error_us;

 	/* allocate a new session keyring */
 	sprintf(desc, "_req.%u", key->serial);

 	cred = get_current_cred();
 	keyring = keyring_alloc(desc, cred->fsuid, cred->fsgid, cred,
 				KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
 				KEY_ALLOC_QUOTA_OVERRUN, NULL, NULL);
 	put_cred(cred);
 	if (IS_ERR(keyring)) {
 		ret = PTR_ERR(keyring);
 		goto error_alloc;
 	}

 	/* attach the auth key to the session keyring */
 	ret = key_link(keyring, authkey);
 	if (ret < 0)
 		goto error_link;

 	/* record the UID and GID */
 	sprintf(uid_str, "%d", from_kuid(&init_user_ns, cred->fsuid));
 	sprintf(gid_str, "%d", from_kgid(&init_user_ns, cred->fsgid));

 	/* we say which key is under construction */
 	sprintf(key_str, "%d", key->serial);

 	/* we specify the process's default keyrings */
 	sprintf(keyring_str[0], "%d",
 		cred->thread_keyring ? cred->thread_keyring->serial : 0);

 	prkey = 0;
 	if (cred->process_keyring)
 		prkey = cred->process_keyring->serial;
 	sprintf(keyring_str[1], "%d", prkey);

 	session = cred->session_keyring;
 	if (!session)
 		session = user_session;
 	sskey = session->serial;

 	sprintf(keyring_str[2], "%d", sskey);

 	/* set up a minimal environment */
 	i = 0;
 	envp[i++] = "HOME=/";
 	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
 	envp[i] = NULL;

 	/* set up the argument list */
 	i = 0;
 	argv[i++] = (char *)request_key;
 	argv[i++] = (char *)rka->op;
 	argv[i++] = key_str;
 	argv[i++] = uid_str;
 	argv[i++] = gid_str;
 	argv[i++] = keyring_str[0];
 	argv[i++] = keyring_str[1];
 	argv[i++] = keyring_str[2];
 	argv[i] = NULL;

 	/* do it */
 	ret = call_usermodehelper_keys(request_key, 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:
 	key_put(user_session);
 error_us:
 	complete_request_key(authkey, ret);
 	kleave(" = %d", ret);
 	return ret;
 }

 /*
  * Call out to userspace for key construction.
  *
  * Program failure is ignored in favour of key status.
  */
 static int construct_key(struct key *key, const void *callout_info,
 			 size_t callout_len, void *aux,
 			 struct key *dest_keyring)
 {
 	request_key_actor_t actor;
 	struct key *authkey;
 	int ret;

 	kenter("%d,%p,%zu,%p", key->serial, callout_info, callout_len, aux);

 	/* allocate an authorisation key */
 	authkey = request_key_auth_new(key, "create", callout_info, callout_len,
 				       dest_keyring);
 	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;

 	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_INVALIDATED, &authkey->flags));

 	key_put(authkey);
 	kleave(" = %d", ret);
 	return ret;
 }

 /*
  * Get the appropriate destination keyring for the request.
  *
  * The keyring selected is returned with an extra reference upon it which the
  * caller must release.
  */
 static int construct_get_dest_keyring(struct key **_dest_keyring)
 {
 	struct request_key_auth *rka;
 	const struct cred *cred = current_cred();
 	struct key *dest_keyring = *_dest_keyring, *authkey;
 	int ret;

 	kenter("%p", dest_keyring);

 	/* find the appropriate keyring */
 	if (dest_keyring) {
 		/* the caller supplied one */
 		key_get(dest_keyring);
 	} else {
 		bool do_perm_check = true;

 		/* use a default keyring; falling through the cases until we
 		 * find one that we actually have */
 		switch (cred->jit_keyring) {
 		case KEY_REQKEY_DEFL_DEFAULT:
 		case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
 			if (cred->request_key_auth) {
 				authkey = cred->request_key_auth;
 				down_read(&authkey->sem);
 				rka = get_request_key_auth(authkey);
 				if (!test_bit(KEY_FLAG_REVOKED,
 					      &authkey->flags))
 					dest_keyring =
 						key_get(rka->dest_keyring);
 				up_read(&authkey->sem);
 				if (dest_keyring) {
 					do_perm_check = false;
 					break;
 				}
 			}

 			fallthrough;
 		case KEY_REQKEY_DEFL_THREAD_KEYRING:
 			dest_keyring = key_get(cred->thread_keyring);
 			if (dest_keyring)
 				break;

 			fallthrough;
 		case KEY_REQKEY_DEFL_PROCESS_KEYRING:
 			dest_keyring = key_get(cred->process_keyring);
 			if (dest_keyring)
 				break;

 			fallthrough;
 		case KEY_REQKEY_DEFL_SESSION_KEYRING:
 			dest_keyring = key_get(cred->session_keyring);

 			if (dest_keyring)
 				break;

 			fallthrough;
 		case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
 			ret = look_up_user_keyrings(NULL, &dest_keyring);
 			if (ret < 0)
 				return ret;
 			break;

 		case KEY_REQKEY_DEFL_USER_KEYRING:
 			ret = look_up_user_keyrings(&dest_keyring, NULL);
 			if (ret < 0)
 				return ret;
 			break;

 		case KEY_REQKEY_DEFL_GROUP_KEYRING:
 		default:
 			BUG();
 		}

 		/*
 		 * Require Write permission on the keyring.  This is essential
 		 * because the default keyring may be the session keyring, and
 		 * joining a keyring only requires Search permission.
 		 *
 		 * However, this check is skipped for the "requestor keyring" so
 		 * that /sbin/request-key can itself use request_key() to add
 		 * keys to the original requestor's destination keyring.
 		 */
 		if (dest_keyring && do_perm_check) {
 			ret = key_permission(make_key_ref(dest_keyring, 1),
 					     KEY_NEED_WRITE);
 			if (ret) {
 				key_put(dest_keyring);
 				return ret;
 			}
 		}
 	}

 	*_dest_keyring = dest_keyring;
 	kleave(" [dk %d]", key_serial(dest_keyring));
 	return 0;
 }

 /*
  * Allocate a new key in under-construction state and attempt to link it in to
  * the requested keyring.
  *
  * May return a key that's already under construction instead if there was a
  * race between two thread calling request_key().
  */
 static int construct_alloc_key(struct keyring_search_context *ctx,
 			       struct key *dest_keyring,
 			       unsigned long flags,
 			       struct key_user *user,
 			       struct key **_key)
 {
 	struct assoc_array_edit *edit = NULL;
 	struct key *key;
 	key_perm_t perm;
 	key_ref_t key_ref;
 	int ret;

 	kenter("%s,%s,,,",
 	       ctx->index_key.type->name, ctx->index_key.description);

 	*_key = NULL;
 	mutex_lock(&user->cons_lock);

 	perm = KEY_POS_VIEW | KEY_POS_SEARCH | KEY_POS_LINK | KEY_POS_SETATTR;
 	perm |= KEY_USR_VIEW;
 	if (ctx->index_key.type->read)
 		perm |= KEY_POS_READ;
 	if (ctx->index_key.type == &key_type_keyring ||
 	    ctx->index_key.type->update)
 		perm |= KEY_POS_WRITE;

 	key = key_alloc(ctx->index_key.type, ctx->index_key.description,
 			ctx->cred->fsuid, ctx->cred->fsgid, ctx->cred,
 			perm, flags, NULL);
 	if (IS_ERR(key))
 		goto alloc_failed;

 	set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);

 	if (dest_keyring) {
 		ret = __key_link_lock(dest_keyring, &ctx->index_key);
 		if (ret < 0)
 			goto link_lock_failed;
 		ret = __key_link_begin(dest_keyring, &ctx->index_key, &edit);
 		if (ret < 0)
 			goto link_prealloc_failed;
 	}

 	/* 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);

 	rcu_read_lock();
 	key_ref = search_process_keyrings_rcu(ctx);
 	rcu_read_unlock();
 	if (!IS_ERR(key_ref))
 		goto key_already_present;

 	if (dest_keyring)
 		__key_link(dest_keyring, key, &edit);

 	mutex_unlock(&key_construction_mutex);
 	if (dest_keyring)
 		__key_link_end(dest_keyring, &ctx->index_key, edit);
 	mutex_unlock(&user->cons_lock);
 	*_key = key;
 	kleave(" = 0 [%d]", key_serial(key));
 	return 0;

 	/* the key is now present - we tell the caller that we found it by
 	 * returning -EINPROGRESS  */
 key_already_present:
 	key_put(key);
 	mutex_unlock(&key_construction_mutex);
 	key = key_ref_to_ptr(key_ref);
 	if (dest_keyring) {
 		ret = __key_link_check_live_key(dest_keyring, key);
 		if (ret == 0)
 			__key_link(dest_keyring, key, &edit);
 		__key_link_end(dest_keyring, &ctx->index_key, edit);
 		if (ret < 0)
 			goto link_check_failed;
 	}
 	mutex_unlock(&user->cons_lock);
 	*_key = key;
 	kleave(" = -EINPROGRESS [%d]", key_serial(key));
 	return -EINPROGRESS;

 link_check_failed:
 	mutex_unlock(&user->cons_lock);
 	key_put(key);
 	kleave(" = %d [linkcheck]", ret);
 	return ret;

 link_prealloc_failed:
 	__key_link_end(dest_keyring, &ctx->index_key, edit);
 link_lock_failed:
 	mutex_unlock(&user->cons_lock);
 	key_put(key);
 	kleave(" = %d [prelink]", ret);
 	return ret;

 alloc_failed:
 	mutex_unlock(&user->cons_lock);
 	kleave(" = %ld", PTR_ERR(key));
 	return PTR_ERR(key);
 }

 /*
  * Commence key construction.
  */
 static struct key *construct_key_and_link(struct keyring_search_context *ctx,
 					  const char *callout_info,
 					  size_t callout_len,
 					  void *aux,
 					  struct key *dest_keyring,
 					  unsigned long flags)
 {
 	struct key_user *user;
 	struct key *key;
 	int ret;

 	kenter("");

 	if (ctx->index_key.type == &key_type_keyring)
 		return ERR_PTR(-EPERM);

 	ret = construct_get_dest_keyring(&dest_keyring);
 	if (ret)
 		goto error;

 	user = key_user_lookup(current_fsuid());
 	if (!user) {
 		ret = -ENOMEM;
 		goto error_put_dest_keyring;
 	}

 	ret = construct_alloc_key(ctx, dest_keyring, flags, user, &key);
 	key_user_put(user);

 	if (ret == 0) {
 		ret = construct_key(key, callout_info, callout_len, aux,
 				    dest_keyring);
 		if (ret < 0) {
 			kdebug("cons failed");
 			goto construction_failed;
 		}
 	} else if (ret == -EINPROGRESS) {
 		ret = 0;
 	} else {
 		goto error_put_dest_keyring;
 	}

 	key_put(dest_keyring);
 	kleave(" = key %d", key_serial(key));
 	return key;

 construction_failed:
 	key_negate_and_link(key, key_negative_timeout, NULL, NULL);
 	key_put(key);
 error_put_dest_keyring:
 	key_put(dest_keyring);
 error:
 	kleave(" = %d", ret);
 	return ERR_PTR(ret);
 }

 /**
  * request_key_and_link - Request a key and cache it in a keyring.
  * @type: The type of key we want.
  * @description: The searchable description of the key.
  * @domain_tag: The domain in which the key operates.
  * @callout_info: The data to pass to the instantiation upcall (or NULL).
  * @callout_len: The length of callout_info.
  * @aux: Auxiliary data for the upcall.
  * @dest_keyring: Where to cache the key.
  * @flags: Flags to key_alloc().
  *
  * A key matching the specified criteria (type, description, domain_tag) is
  * searched for in the process's keyrings and returned with its usage count
  * incremented if found.  Otherwise, if callout_info is not NULL, a key will be
  * allocated and some service (probably in userspace) will be asked to
  * instantiate it.
  *
  * If successfully found or created, the key will be linked to the destination
  * keyring if one is provided.
  *
  * Returns a pointer to the key if successful; -EACCES, -ENOKEY, -EKEYREVOKED
  * or -EKEYEXPIRED if an inaccessible, negative, revoked or expired key was
  * found; -ENOKEY if no key was found and no @callout_info was given; -EDQUOT
  * if insufficient key quota was available to create a new key; or -ENOMEM if
  * insufficient memory was available.
  *
  * If the returned key was created, then it may still be under construction,
  * and wait_for_key_construction() should be used to wait for that to complete.
  */
 struct key *request_key_and_link(struct key_type *type,
 				 const char *description,
 				 struct key_tag *domain_tag,
 				 const void *callout_info,
 				 size_t callout_len,
 				 void *aux,
 				 struct key *dest_keyring,
 				 unsigned long flags)
 {
 	struct keyring_search_context ctx = {
 		.index_key.type		= type,
 		.index_key.domain_tag	= domain_tag,
 		.index_key.description	= description,
 		.index_key.desc_len	= strlen(description),
 		.cred			= current_cred(),
 		.match_data.cmp		= key_default_cmp,
 		.match_data.raw_data	= description,
 		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
 		.flags			= (KEYRING_SEARCH_DO_STATE_CHECK |
 					   KEYRING_SEARCH_SKIP_EXPIRED |
 					   KEYRING_SEARCH_RECURSE),
 	};
 	struct key *key;
 	key_ref_t key_ref;
 	int ret;

 	kenter("%s,%s,%p,%zu,%p,%p,%lx",
 	       ctx.index_key.type->name, ctx.index_key.description,
 	       callout_info, callout_len, aux, dest_keyring, flags);

 	if (type->match_preparse) {
 		ret = type->match_preparse(&ctx.match_data);
 		if (ret < 0) {
 			key = ERR_PTR(ret);
 			goto error;
 		}
 	}

 	key = check_cached_key(&ctx);
 	if (key)
 		goto error_free;

 	/* search all the process keyrings for a key */
 	rcu_read_lock();
 	key_ref = search_process_keyrings_rcu(&ctx);
 	rcu_read_unlock();

 	if (!IS_ERR(key_ref)) {
 		if (dest_keyring) {
 			ret = key_task_permission(key_ref, current_cred(),
 						  KEY_NEED_LINK);
 			if (ret < 0) {
 				key_ref_put(key_ref);
 				key = ERR_PTR(ret);
 				goto error_free;
 			}
 		}

 		key = key_ref_to_ptr(key_ref);
 		if (dest_keyring) {
 			ret = key_link(dest_keyring, key);
 			if (ret < 0) {
 				key_put(key);
 				key = ERR_PTR(ret);
 				goto error_free;
 			}
 		}

 		/* Only cache the key on immediate success */
 		cache_requested_key(key);
 	} else if (PTR_ERR(key_ref) != -EAGAIN) {
 		key = ERR_CAST(key_ref);
 	} 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_free;

 		key = construct_key_and_link(&ctx, callout_info, callout_len,
 					     aux, dest_keyring, flags);
 	}

 error_free:
 	if (type->match_free)
 		type->match_free(&ctx.match_data);
 error:
 	kleave(" = %p", key);
 	return key;
 }

 /**
  * wait_for_key_construction - Wait for construction of a key to complete
  * @key: The key being waited for.
  * @intr: Whether to wait interruptibly.
  *
  * Wait for a key to finish being constructed.
  *
  * Returns 0 if successful; -ERESTARTSYS if the wait was interrupted; -ENOKEY
  * if the key was negated; or -EKEYREVOKED or -EKEYEXPIRED if the key was
  * revoked or expired.
  */
 int wait_for_key_construction(struct key *key, bool intr)
 {
 	int ret;

 	ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
 			  intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
 	if (ret)
 		return -ERESTARTSYS;
 	ret = key_read_state(key);
 	if (ret < 0)
 		return ret;
 	return key_validate(key);
 }
 EXPORT_SYMBOL(wait_for_key_construction);

 /**
  * request_key_tag - Request a key and wait for construction
  * @type: Type of key.
  * @description: The searchable description of the key.
  * @domain_tag: The domain in which the key operates.
  * @callout_info: The data to pass to the instantiation upcall (or NULL).
  *
  * As for request_key_and_link() except that it does not add the returned key
  * to a keyring if found, new keys are always allocated in the user's quota,
  * the callout_info must be a NUL-terminated string and no auxiliary data can
  * be passed.
  *
  * Furthermore, it then works as wait_for_key_construction() to wait for the
  * completion of keys undergoing construction with a non-interruptible wait.
  */
 struct key *request_key_tag(struct key_type *type,
 			    const char *description,
 			    struct key_tag *domain_tag,
 			    const char *callout_info)
 {
 	struct key *key;
 	size_t callout_len = 0;
 	int ret;

 	if (callout_info)
 		callout_len = strlen(callout_info);
 	key = request_key_and_link(type, description, domain_tag,
 				   callout_info, callout_len,
 				   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_tag);

 /**
  * request_key_with_auxdata - Request a key with auxiliary data for the upcaller
  * @type: The type of key we want.
  * @description: The searchable description of the key.
  * @domain_tag: The domain in which the key operates.
  * @callout_info: The data to pass to the instantiation upcall (or NULL).
  * @callout_len: The length of callout_info.
  * @aux: Auxiliary data for the upcall.
  *
  * As for request_key_and_link() except that it does not add the returned key
  * to a keyring if found and new keys are always allocated in the user's quota.
  *
  * Furthermore, it then works as wait_for_key_construction() to wait for the
  * completion of keys undergoing construction with a non-interruptible wait.
  */
 struct key *request_key_with_auxdata(struct key_type *type,
 				     const char *description,
 				     struct key_tag *domain_tag,
 				     const void *callout_info,
 				     size_t callout_len,
 				     void *aux)
 {
 	struct key *key;
 	int ret;

 	key = request_key_and_link(type, description, domain_tag,
 				   callout_info, callout_len,
 				   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);

 /**
  * request_key_rcu - Request key from RCU-read-locked context
  * @type: The type of key we want.
  * @description: The name of the key we want.
  * @domain_tag: The domain in which the key operates.
  *
  * Request a key from a context that we may not sleep in (such as RCU-mode
  * pathwalk).  Keys under construction are ignored.
  *
  * Return a pointer to the found key if successful, -ENOKEY if we couldn't find
  * a key or some other error if the key found was unsuitable or inaccessible.
  */
 struct key *request_key_rcu(struct key_type *type,
 			    const char *description,
 			    struct key_tag *domain_tag)
 {
 	struct keyring_search_context ctx = {
 		.index_key.type		= type,
 		.index_key.domain_tag	= domain_tag,
 		.index_key.description	= description,
 		.index_key.desc_len	= strlen(description),
 		.cred			= current_cred(),
 		.match_data.cmp		= key_default_cmp,
 		.match_data.raw_data	= description,
 		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
 		.flags			= (KEYRING_SEARCH_DO_STATE_CHECK |
 					   KEYRING_SEARCH_SKIP_EXPIRED),
 	};
 	struct key *key;
 	key_ref_t key_ref;

 	kenter("%s,%s", type->name, description);

 	key = check_cached_key(&ctx);
 	if (key)
 		return key;

 	/* search all the process keyrings for a key */
 	key_ref = search_process_keyrings_rcu(&ctx);
 	if (IS_ERR(key_ref)) {
 		key = ERR_CAST(key_ref);
 		if (PTR_ERR(key_ref) == -EAGAIN)
 			key = ERR_PTR(-ENOKEY);
 	} else {
 		key = key_ref_to_ptr(key_ref);
 		cache_requested_key(key);
 	}

 	kleave(" = %p", key);
 	return key;
 }
 EXPORT_SYMBOL(request_key_rcu);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/* Request a key from userspace
	*
	* Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
	* Written by David Howells (dhowells@redhat.com)
	*
	* See Documentation/security/keys/request-key.rst
	*/

	#include <linux/export.h>
	#include <linux/sched.h>
	#include <linux/kmod.h>
	#include <linux/err.h>
	#include <linux/keyctl.h>
	#include <linux/slab.h>
	#include <net/net_namespace.h>
	#include "internal.h"
	#include <keys/request_key_auth-type.h>

	#define key_negative_timeout 60 /* default timeout on a negative key's existence */

	static struct key check_cached_key(struct keyring_search_context ctx)
	{
	#ifdef CONFIG_KEYS_REQUEST_CACHE
	struct key *key = current->cached_requested_key;

	if (key &&
	ctx->match_data.cmp(key, &ctx->match_data) &&
	!(key->flags & ((1 << KEY_FLAG_INVALIDATED) \|
	(1 << KEY_FLAG_REVOKED))))
	return key_get(key);
	#endif
	return NULL;
	}

	static void cache_requested_key(struct key *key)
	{
	#ifdef CONFIG_KEYS_REQUEST_CACHE
	struct task_struct *t = current;

	key_put(t->cached_requested_key);
	t->cached_requested_key = key_get(key);
	set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
	#endif
	}

	/**
	* complete_request_key - Complete the construction of a key.
	* @authkey: 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 *authkey, int 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(key, key_negative_timeout, NULL, authkey);
	else
	key_revoke(authkey);
	}
	EXPORT_SYMBOL(complete_request_key);

	/*
	* Initialise a usermode helper that is going to have a specific session
	* keyring.
	*
	* This is called in context of freshly forked kthread before kernel_execve(),
	* so we can simply install the desired session_keyring at this point.
	*/
	static int umh_keys_init(struct subprocess_info info, struct cred cred)
	{
	struct key *keyring = info->data;

	return install_session_keyring_to_cred(cred, keyring);
	}

	/*
	* Clean up a usermode helper with session keyring.
	*/
	static void umh_keys_cleanup(struct subprocess_info *info)
	{
	struct key *keyring = info->data;
	key_put(keyring);
	}

	/*
	* Call a usermode helper with a specific session keyring.
	*/
	static int call_usermodehelper_keys(const char path, char argv, char *envp,
	struct key *session_keyring, int wait)
	{
	struct subprocess_info *info;

	info = call_usermodehelper_setup(path, argv, envp, GFP_KERNEL,
	umh_keys_init, umh_keys_cleanup,
	session_keyring);
	if (!info)
	return -ENOMEM;

	key_get(session_keyring);
	return call_usermodehelper_exec(info, wait);
	}

	/*
	* 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 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 = rka->target_key, keyring, session, user_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, rka->op);

	ret = look_up_user_keyrings(NULL, &user_session);
	if (ret < 0)
	goto error_us;

	/* allocate a new session keyring */
	sprintf(desc, "_req.%u", key->serial);

	cred = get_current_cred();
	keyring = keyring_alloc(desc, cred->fsuid, cred->fsgid, cred,
	KEY_POS_ALL \| KEY_USR_VIEW \| KEY_USR_READ,
	KEY_ALLOC_QUOTA_OVERRUN, NULL, NULL);
	put_cred(cred);
	if (IS_ERR(keyring)) {
	ret = PTR_ERR(keyring);
	goto error_alloc;
	}

	/* attach the auth key to the session keyring */
	ret = key_link(keyring, authkey);
	if (ret < 0)
	goto error_link;

	/* record the UID and GID */
	sprintf(uid_str, "%d", from_kuid(&init_user_ns, cred->fsuid));
	sprintf(gid_str, "%d", from_kgid(&init_user_ns, cred->fsgid));

	/* we say which key is under construction */
	sprintf(key_str, "%d", key->serial);

	/* we specify the process's default keyrings */
	sprintf(keyring_str[0], "%d",
	cred->thread_keyring ? cred->thread_keyring->serial : 0);

	prkey = 0;
	if (cred->process_keyring)
	prkey = cred->process_keyring->serial;
	sprintf(keyring_str[1], "%d", prkey);

	session = cred->session_keyring;
	if (!session)
	session = user_session;
	sskey = session->serial;

	sprintf(keyring_str[2], "%d", sskey);

	/* set up a minimal environment */
	i = 0;
	envp[i++] = "HOME=/";
	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
	envp[i] = NULL;

	/* set up the argument list */
	i = 0;
	argv[i++] = (char *)request_key;
	argv[i++] = (char *)rka->op;
	argv[i++] = key_str;
	argv[i++] = uid_str;
	argv[i++] = gid_str;
	argv[i++] = keyring_str[0];
	argv[i++] = keyring_str[1];
	argv[i++] = keyring_str[2];
	argv[i] = NULL;

	/* do it */
	ret = call_usermodehelper_keys(request_key, 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:
	key_put(user_session);
	error_us:
	complete_request_key(authkey, ret);
	kleave(" = %d", ret);
	return ret;
	}

	/*
	* Call out to userspace for key construction.
	*
	* Program failure is ignored in favour of key status.
	*/
	static int construct_key(struct key key, const void callout_info,
	size_t callout_len, void *aux,
	struct key *dest_keyring)
	{
	request_key_actor_t actor;
	struct key *authkey;
	int ret;

	kenter("%d,%p,%zu,%p", key->serial, callout_info, callout_len, aux);

	/* allocate an authorisation key */
	authkey = request_key_auth_new(key, "create", callout_info, callout_len,
	dest_keyring);
	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;

	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_INVALIDATED, &authkey->flags));

	key_put(authkey);
	kleave(" = %d", ret);
	return ret;
	}

	/*
	* Get the appropriate destination keyring for the request.
	*
	* The keyring selected is returned with an extra reference upon it which the
	* caller must release.
	*/
	static int construct_get_dest_keyring(struct key **_dest_keyring)
	{
	struct request_key_auth *rka;
	const struct cred *cred = current_cred();
	struct key dest_keyring = _dest_keyring, *authkey;
	int ret;

	kenter("%p", dest_keyring);

	/* find the appropriate keyring */
	if (dest_keyring) {
	/* the caller supplied one */
	key_get(dest_keyring);
	} else {
	bool do_perm_check = true;

	/* use a default keyring; falling through the cases until we
	* find one that we actually have */
	switch (cred->jit_keyring) {
	case KEY_REQKEY_DEFL_DEFAULT:
	case KEY_REQKEY_DEFL_REQUESTOR_KEYRING:
	if (cred->request_key_auth) {
	authkey = cred->request_key_auth;
	down_read(&authkey->sem);
	rka = get_request_key_auth(authkey);
	if (!test_bit(KEY_FLAG_REVOKED,
	&authkey->flags))
	dest_keyring =
	key_get(rka->dest_keyring);
	up_read(&authkey->sem);
	if (dest_keyring) {
	do_perm_check = false;
	break;
	}
	}

	fallthrough;
	case KEY_REQKEY_DEFL_THREAD_KEYRING:
	dest_keyring = key_get(cred->thread_keyring);
	if (dest_keyring)
	break;

	fallthrough;
	case KEY_REQKEY_DEFL_PROCESS_KEYRING:
	dest_keyring = key_get(cred->process_keyring);
	if (dest_keyring)
	break;

	fallthrough;
	case KEY_REQKEY_DEFL_SESSION_KEYRING:
	dest_keyring = key_get(cred->session_keyring);

	if (dest_keyring)
	break;

	fallthrough;
	case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
	ret = look_up_user_keyrings(NULL, &dest_keyring);
	if (ret < 0)
	return ret;
	break;

	case KEY_REQKEY_DEFL_USER_KEYRING:
	ret = look_up_user_keyrings(&dest_keyring, NULL);
	if (ret < 0)
	return ret;
	break;

	case KEY_REQKEY_DEFL_GROUP_KEYRING:
	default:
	BUG();
	}

	/*
	* Require Write permission on the keyring. This is essential
	* because the default keyring may be the session keyring, and
	* joining a keyring only requires Search permission.
	*
	* However, this check is skipped for the "requestor keyring" so
	* that /sbin/request-key can itself use request_key() to add
	* keys to the original requestor's destination keyring.
	*/
	if (dest_keyring && do_perm_check) {
	ret = key_permission(make_key_ref(dest_keyring, 1),
	KEY_NEED_WRITE);
	if (ret) {
	key_put(dest_keyring);
	return ret;
	}
	}
	}

	*_dest_keyring = dest_keyring;
	kleave(" [dk %d]", key_serial(dest_keyring));
	return 0;
	}

	/*
	* Allocate a new key in under-construction state and attempt to link it in to
	* the requested keyring.
	*
	* May return a key that's already under construction instead if there was a
	* race between two thread calling request_key().
	*/
	static int construct_alloc_key(struct keyring_search_context *ctx,
	struct key *dest_keyring,
	unsigned long flags,
	struct key_user *user,
	struct key **_key)
	{
	struct assoc_array_edit *edit = NULL;
	struct key *key;
	key_perm_t perm;
	key_ref_t key_ref;
	int ret;

	kenter("%s,%s,,,",
	ctx->index_key.type->name, ctx->index_key.description);

	*_key = NULL;
	mutex_lock(&user->cons_lock);

	perm = KEY_POS_VIEW \| KEY_POS_SEARCH \| KEY_POS_LINK \| KEY_POS_SETATTR;
	perm \|= KEY_USR_VIEW;
	if (ctx->index_key.type->read)
	perm \|= KEY_POS_READ;
	if (ctx->index_key.type == &key_type_keyring \|\|
	ctx->index_key.type->update)
	perm \|= KEY_POS_WRITE;

	key = key_alloc(ctx->index_key.type, ctx->index_key.description,
	ctx->cred->fsuid, ctx->cred->fsgid, ctx->cred,
	perm, flags, NULL);
	if (IS_ERR(key))
	goto alloc_failed;

	set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);

	if (dest_keyring) {
	ret = __key_link_lock(dest_keyring, &ctx->index_key);
	if (ret < 0)
	goto link_lock_failed;
	ret = __key_link_begin(dest_keyring, &ctx->index_key, &edit);
	if (ret < 0)
	goto link_prealloc_failed;
	}

	/* 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);

	rcu_read_lock();
	key_ref = search_process_keyrings_rcu(ctx);
	rcu_read_unlock();
	if (!IS_ERR(key_ref))
	goto key_already_present;

	if (dest_keyring)
	__key_link(dest_keyring, key, &edit);

	mutex_unlock(&key_construction_mutex);
	if (dest_keyring)
	__key_link_end(dest_keyring, &ctx->index_key, edit);
	mutex_unlock(&user->cons_lock);
	*_key = key;
	kleave(" = 0 [%d]", key_serial(key));
	return 0;

	/* the key is now present - we tell the caller that we found it by
	* returning -EINPROGRESS */
	key_already_present:
	key_put(key);
	mutex_unlock(&key_construction_mutex);
	key = key_ref_to_ptr(key_ref);
	if (dest_keyring) {
	ret = __key_link_check_live_key(dest_keyring, key);
	if (ret == 0)
	__key_link(dest_keyring, key, &edit);
	__key_link_end(dest_keyring, &ctx->index_key, edit);
	if (ret < 0)
	goto link_check_failed;
	}
	mutex_unlock(&user->cons_lock);
	*_key = key;
	kleave(" = -EINPROGRESS [%d]", key_serial(key));
	return -EINPROGRESS;

	link_check_failed:
	mutex_unlock(&user->cons_lock);
	key_put(key);
	kleave(" = %d [linkcheck]", ret);
	return ret;

	link_prealloc_failed:
	__key_link_end(dest_keyring, &ctx->index_key, edit);
	link_lock_failed:
	mutex_unlock(&user->cons_lock);
	key_put(key);
	kleave(" = %d [prelink]", ret);
	return ret;

	alloc_failed:
	mutex_unlock(&user->cons_lock);
	kleave(" = %ld", PTR_ERR(key));
	return PTR_ERR(key);
	}

	/*
	* Commence key construction.
	*/
	static struct key construct_key_and_link(struct keyring_search_context ctx,
	const char *callout_info,
	size_t callout_len,
	void *aux,
	struct key *dest_keyring,
	unsigned long flags)
	{
	struct key_user *user;
	struct key *key;
	int ret;

	kenter("");

	if (ctx->index_key.type == &key_type_keyring)
	return ERR_PTR(-EPERM);

	ret = construct_get_dest_keyring(&dest_keyring);
	if (ret)
	goto error;

	user = key_user_lookup(current_fsuid());
	if (!user) {
	ret = -ENOMEM;
	goto error_put_dest_keyring;
	}

	ret = construct_alloc_key(ctx, dest_keyring, flags, user, &key);
	key_user_put(user);

	if (ret == 0) {
	ret = construct_key(key, callout_info, callout_len, aux,
	dest_keyring);
	if (ret < 0) {
	kdebug("cons failed");
	goto construction_failed;
	}
	} else if (ret == -EINPROGRESS) {
	ret = 0;
	} else {
	goto error_put_dest_keyring;
	}

	key_put(dest_keyring);
	kleave(" = key %d", key_serial(key));
	return key;

	construction_failed:
	key_negate_and_link(key, key_negative_timeout, NULL, NULL);
	key_put(key);
	error_put_dest_keyring:
	key_put(dest_keyring);
	error:
	kleave(" = %d", ret);
	return ERR_PTR(ret);
	}

	/**
	* request_key_and_link - Request a key and cache it in a keyring.
	* @type: The type of key we want.
	* @description: The searchable description of the key.
	* @domain_tag: The domain in which the key operates.
	* @callout_info: The data to pass to the instantiation upcall (or NULL).
	* @callout_len: The length of callout_info.
	* @aux: Auxiliary data for the upcall.
	* @dest_keyring: Where to cache the key.
	* @flags: Flags to key_alloc().
	*
	* A key matching the specified criteria (type, description, domain_tag) is
	* searched for in the process's keyrings and returned with its usage count
	* incremented if found. Otherwise, if callout_info is not NULL, a key will be
	* allocated and some service (probably in userspace) will be asked to
	* instantiate it.
	*
	* If successfully found or created, the key will be linked to the destination
	* keyring if one is provided.
	*
	* Returns a pointer to the key if successful; -EACCES, -ENOKEY, -EKEYREVOKED
	* or -EKEYEXPIRED if an inaccessible, negative, revoked or expired key was
	* found; -ENOKEY if no key was found and no @callout_info was given; -EDQUOT
	* if insufficient key quota was available to create a new key; or -ENOMEM if
	* insufficient memory was available.
	*
	* If the returned key was created, then it may still be under construction,
	* and wait_for_key_construction() should be used to wait for that to complete.
	*/
	struct key request_key_and_link(struct key_type type,
	const char *description,
	struct key_tag *domain_tag,
	const void *callout_info,
	size_t callout_len,
	void *aux,
	struct key *dest_keyring,
	unsigned long flags)
	{
	struct keyring_search_context ctx = {
	.index_key.type = type,
	.index_key.domain_tag = domain_tag,
	.index_key.description = description,
	.index_key.desc_len = strlen(description),
	.cred = current_cred(),
	.match_data.cmp = key_default_cmp,
	.match_data.raw_data = description,
	.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
	.flags = (KEYRING_SEARCH_DO_STATE_CHECK \|
	KEYRING_SEARCH_SKIP_EXPIRED \|
	KEYRING_SEARCH_RECURSE),
	};
	struct key *key;
	key_ref_t key_ref;
	int ret;

	kenter("%s,%s,%p,%zu,%p,%p,%lx",
	ctx.index_key.type->name, ctx.index_key.description,
	callout_info, callout_len, aux, dest_keyring, flags);

	if (type->match_preparse) {
	ret = type->match_preparse(&ctx.match_data);
	if (ret < 0) {
	key = ERR_PTR(ret);
	goto error;
	}
	}

	key = check_cached_key(&ctx);
	if (key)
	goto error_free;

	/* search all the process keyrings for a key */
	rcu_read_lock();
	key_ref = search_process_keyrings_rcu(&ctx);
	rcu_read_unlock();

	if (!IS_ERR(key_ref)) {
	if (dest_keyring) {
	ret = key_task_permission(key_ref, current_cred(),
	KEY_NEED_LINK);
	if (ret < 0) {
	key_ref_put(key_ref);
	key = ERR_PTR(ret);
	goto error_free;
	}
	}

	key = key_ref_to_ptr(key_ref);
	if (dest_keyring) {
	ret = key_link(dest_keyring, key);
	if (ret < 0) {
	key_put(key);
	key = ERR_PTR(ret);
	goto error_free;
	}
	}

	/* Only cache the key on immediate success */
	cache_requested_key(key);
	} else if (PTR_ERR(key_ref) != -EAGAIN) {
	key = ERR_CAST(key_ref);
	} 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_free;

	key = construct_key_and_link(&ctx, callout_info, callout_len,
	aux, dest_keyring, flags);
	}

	error_free:
	if (type->match_free)
	type->match_free(&ctx.match_data);
	error:
	kleave(" = %p", key);
	return key;
	}

	/**
	* wait_for_key_construction - Wait for construction of a key to complete
	* @key: The key being waited for.
	* @intr: Whether to wait interruptibly.
	*
	* Wait for a key to finish being constructed.
	*
	* Returns 0 if successful; -ERESTARTSYS if the wait was interrupted; -ENOKEY
	* if the key was negated; or -EKEYREVOKED or -EKEYEXPIRED if the key was
	* revoked or expired.
	*/
	int wait_for_key_construction(struct key *key, bool intr)
	{
	int ret;

	ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
	intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
	if (ret)
	return -ERESTARTSYS;
	ret = key_read_state(key);
	if (ret < 0)
	return ret;
	return key_validate(key);
	}
	EXPORT_SYMBOL(wait_for_key_construction);

	/**
	* request_key_tag - Request a key and wait for construction
	* @type: Type of key.
	* @description: The searchable description of the key.
	* @domain_tag: The domain in which the key operates.
	* @callout_info: The data to pass to the instantiation upcall (or NULL).
	*
	* As for request_key_and_link() except that it does not add the returned key
	* to a keyring if found, new keys are always allocated in the user's quota,
	* the callout_info must be a NUL-terminated string and no auxiliary data can
	* be passed.
	*
	* Furthermore, it then works as wait_for_key_construction() to wait for the
	* completion of keys undergoing construction with a non-interruptible wait.
	*/
	struct key request_key_tag(struct key_type type,
	const char *description,
	struct key_tag *domain_tag,
	const char *callout_info)
	{
	struct key *key;
	size_t callout_len = 0;
	int ret;

	if (callout_info)
	callout_len = strlen(callout_info);
	key = request_key_and_link(type, description, domain_tag,
	callout_info, callout_len,
	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_tag);

	/**
	* request_key_with_auxdata - Request a key with auxiliary data for the upcaller
	* @type: The type of key we want.
	* @description: The searchable description of the key.
	* @domain_tag: The domain in which the key operates.
	* @callout_info: The data to pass to the instantiation upcall (or NULL).
	* @callout_len: The length of callout_info.
	* @aux: Auxiliary data for the upcall.
	*
	* As for request_key_and_link() except that it does not add the returned key
	* to a keyring if found and new keys are always allocated in the user's quota.
	*
	* Furthermore, it then works as wait_for_key_construction() to wait for the
	* completion of keys undergoing construction with a non-interruptible wait.
	*/
	struct key request_key_with_auxdata(struct key_type type,
	const char *description,
	struct key_tag *domain_tag,
	const void *callout_info,
	size_t callout_len,
	void *aux)
	{
	struct key *key;
	int ret;

	key = request_key_and_link(type, description, domain_tag,
	callout_info, callout_len,
	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);

	/**
	* request_key_rcu - Request key from RCU-read-locked context
	* @type: The type of key we want.
	* @description: The name of the key we want.
	* @domain_tag: The domain in which the key operates.
	*
	* Request a key from a context that we may not sleep in (such as RCU-mode
	* pathwalk). Keys under construction are ignored.
	*
	* Return a pointer to the found key if successful, -ENOKEY if we couldn't find
	* a key or some other error if the key found was unsuitable or inaccessible.
	*/
	struct key request_key_rcu(struct key_type type,
	const char *description,
	struct key_tag *domain_tag)
	{
	struct keyring_search_context ctx = {
	.index_key.type = type,
	.index_key.domain_tag = domain_tag,
	.index_key.description = description,
	.index_key.desc_len = strlen(description),
	.cred = current_cred(),
	.match_data.cmp = key_default_cmp,
	.match_data.raw_data = description,
	.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
	.flags = (KEYRING_SEARCH_DO_STATE_CHECK \|
	KEYRING_SEARCH_SKIP_EXPIRED),
	};
	struct key *key;
	key_ref_t key_ref;

	kenter("%s,%s", type->name, description);

	key = check_cached_key(&ctx);
	if (key)
	return key;

	/* search all the process keyrings for a key */
	key_ref = search_process_keyrings_rcu(&ctx);
	if (IS_ERR(key_ref)) {
	key = ERR_CAST(key_ref);
	if (PTR_ERR(key_ref) == -EAGAIN)
	key = ERR_PTR(-ENOKEY);
	} else {
	key = key_ref_to_ptr(key_ref);
	cache_requested_key(key);
	}

	kleave(" = %p", key);
	return key;
	}
	EXPORT_SYMBOL(request_key_rcu);