Merge tag 'mmc-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc

[mirror_ubuntu-hirsute-kernel.git] / security / keys / process_keys.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Manage a process's keyrings
 *
 * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/keyctl.h>
#include <linux/fs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/security.h>
#include <linux/user_namespace.h>
#include <linux/uaccess.h>
#include <linux/init_task.h>
#include <keys/request_key_auth-type.h>
#include "internal.h"

/* Session keyring create vs join semaphore */
static DEFINE_MUTEX(key_session_mutex);

/* The root user's tracking struct */
struct key_user root_key_user = {
        .usage          = REFCOUNT_INIT(3),
        .cons_lock      = __MUTEX_INITIALIZER(root_key_user.cons_lock),
        .lock           = __SPIN_LOCK_UNLOCKED(root_key_user.lock),
        .nkeys          = ATOMIC_INIT(2),
        .nikeys         = ATOMIC_INIT(2),
        .uid            = GLOBAL_ROOT_UID,
};

/*
 * Get or create a user register keyring.
 */
static struct key *get_user_register(struct user_namespace *user_ns)
{
        struct key *reg_keyring = READ_ONCE(user_ns->user_keyring_register);

        if (reg_keyring)
                return reg_keyring;

        down_write(&user_ns->keyring_sem);

        /* Make sure there's a register keyring.  It gets owned by the
         * user_namespace's owner.
         */
        reg_keyring = user_ns->user_keyring_register;
        if (!reg_keyring) {
                reg_keyring = keyring_alloc(".user_reg",
                                            user_ns->owner, INVALID_GID,
                                            &init_cred,
                                            KEY_POS_WRITE | KEY_POS_SEARCH |
                                            KEY_USR_VIEW | KEY_USR_READ,
                                            0,
                                            NULL, NULL);
                if (!IS_ERR(reg_keyring))
                        smp_store_release(&user_ns->user_keyring_register,
                                          reg_keyring);
        }

        up_write(&user_ns->keyring_sem);

        /* We don't return a ref since the keyring is pinned by the user_ns */
        return reg_keyring;
}

/*
 * Look up the user and user session keyrings for the current process's UID,
 * creating them if they don't exist.
 */
int look_up_user_keyrings(struct key **_user_keyring,
                          struct key **_user_session_keyring)
{
        const struct cred *cred = current_cred();
        struct user_namespace *user_ns = current_user_ns();
        struct key *reg_keyring, *uid_keyring, *session_keyring;
        key_perm_t user_keyring_perm;
        key_ref_t uid_keyring_r, session_keyring_r;
        uid_t uid = from_kuid(user_ns, cred->user->uid);
        char buf[20];
        int ret;

        user_keyring_perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL;

        kenter("%u", uid);

        reg_keyring = get_user_register(user_ns);
        if (IS_ERR(reg_keyring))
                return PTR_ERR(reg_keyring);

        down_write(&user_ns->keyring_sem);
        ret = 0;

        /* Get the user keyring.  Note that there may be one in existence
         * already as it may have been pinned by a session, but the user_struct
         * pointing to it may have been destroyed by setuid.
         */
        snprintf(buf, sizeof(buf), "_uid.%u", uid);
        uid_keyring_r = keyring_search(make_key_ref(reg_keyring, true),
                                       &key_type_keyring, buf, false);
        kdebug("_uid %p", uid_keyring_r);
        if (uid_keyring_r == ERR_PTR(-EAGAIN)) {
                uid_keyring = keyring_alloc(buf, cred->user->uid, INVALID_GID,
                                            cred, user_keyring_perm,
                                            KEY_ALLOC_UID_KEYRING |
                                            KEY_ALLOC_IN_QUOTA,
                                            NULL, reg_keyring);
                if (IS_ERR(uid_keyring)) {
                        ret = PTR_ERR(uid_keyring);
                        goto error;
                }
        } else if (IS_ERR(uid_keyring_r)) {
                ret = PTR_ERR(uid_keyring_r);
                goto error;
        } else {
                uid_keyring = key_ref_to_ptr(uid_keyring_r);
        }

        /* Get a default session keyring (which might also exist already) */
        snprintf(buf, sizeof(buf), "_uid_ses.%u", uid);
        session_keyring_r = keyring_search(make_key_ref(reg_keyring, true),
                                           &key_type_keyring, buf, false);
        kdebug("_uid_ses %p", session_keyring_r);
        if (session_keyring_r == ERR_PTR(-EAGAIN)) {
                session_keyring = keyring_alloc(buf, cred->user->uid, INVALID_GID,
                                                cred, user_keyring_perm,
                                                KEY_ALLOC_UID_KEYRING |
                                                KEY_ALLOC_IN_QUOTA,
                                                NULL, NULL);
                if (IS_ERR(session_keyring)) {
                        ret = PTR_ERR(session_keyring);
                        goto error_release;
                }

                /* We install a link from the user session keyring to
                 * the user keyring.
                 */
                ret = key_link(session_keyring, uid_keyring);
                if (ret < 0)
                        goto error_release_session;

                /* And only then link the user-session keyring to the
                 * register.
                 */
                ret = key_link(reg_keyring, session_keyring);
                if (ret < 0)
                        goto error_release_session;
        } else if (IS_ERR(session_keyring_r)) {
                ret = PTR_ERR(session_keyring_r);
                goto error_release;
        } else {
                session_keyring = key_ref_to_ptr(session_keyring_r);
        }

        up_write(&user_ns->keyring_sem);

        if (_user_session_keyring)
                *_user_session_keyring = session_keyring;
        else
                key_put(session_keyring);
        if (_user_keyring)
                *_user_keyring = uid_keyring;
        else
                key_put(uid_keyring);
        kleave(" = 0");
        return 0;

error_release_session:
        key_put(session_keyring);
error_release:
        key_put(uid_keyring);
error:
        up_write(&user_ns->keyring_sem);
        kleave(" = %d", ret);
        return ret;
}

/*
 * Get the user session keyring if it exists, but don't create it if it
 * doesn't.
 */
struct key *get_user_session_keyring_rcu(const struct cred *cred)
{
        struct key *reg_keyring = READ_ONCE(cred->user_ns->user_keyring_register);
        key_ref_t session_keyring_r;
        char buf[20];

        struct keyring_search_context ctx = {
                .index_key.type         = &key_type_keyring,
                .index_key.description  = buf,
                .cred                   = cred,
                .match_data.cmp         = key_default_cmp,
                .match_data.raw_data    = buf,
                .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
                .flags                  = KEYRING_SEARCH_DO_STATE_CHECK,
        };

        if (!reg_keyring)
                return NULL;

        ctx.index_key.desc_len = snprintf(buf, sizeof(buf), "_uid_ses.%u",
                                          from_kuid(cred->user_ns,
                                                    cred->user->uid));

        session_keyring_r = keyring_search_rcu(make_key_ref(reg_keyring, true),
                                               &ctx);
        if (IS_ERR(session_keyring_r))
                return NULL;
        return key_ref_to_ptr(session_keyring_r);
}

/*
 * Install a thread keyring to the given credentials struct if it didn't have
 * one already.  This is allowed to overrun the quota.
 *
 * Return: 0 if a thread keyring is now present; -errno on failure.
 */
int install_thread_keyring_to_cred(struct cred *new)
{
        struct key *keyring;

        if (new->thread_keyring)
                return 0;

        keyring = keyring_alloc("_tid", new->uid, new->gid, new,
                                KEY_POS_ALL | KEY_USR_VIEW,
                                KEY_ALLOC_QUOTA_OVERRUN,
                                NULL, NULL);
        if (IS_ERR(keyring))
                return PTR_ERR(keyring);

        new->thread_keyring = keyring;
        return 0;
}

/*
 * Install a thread keyring to the current task if it didn't have one already.
 *
 * Return: 0 if a thread keyring is now present; -errno on failure.
 */
static int install_thread_keyring(void)
{
        struct cred *new;
        int ret;

        new = prepare_creds();
        if (!new)
                return -ENOMEM;

        ret = install_thread_keyring_to_cred(new);
        if (ret < 0) {
                abort_creds(new);
                return ret;
        }

        return commit_creds(new);
}

/*
 * Install a process keyring to the given credentials struct if it didn't have
 * one already.  This is allowed to overrun the quota.
 *
 * Return: 0 if a process keyring is now present; -errno on failure.
 */
int install_process_keyring_to_cred(struct cred *new)
{
        struct key *keyring;

        if (new->process_keyring)
                return 0;

        keyring = keyring_alloc("_pid", new->uid, new->gid, new,
                                KEY_POS_ALL | KEY_USR_VIEW,
                                KEY_ALLOC_QUOTA_OVERRUN,
                                NULL, NULL);
        if (IS_ERR(keyring))
                return PTR_ERR(keyring);

        new->process_keyring = keyring;
        return 0;
}

/*
 * Install a process keyring to the current task if it didn't have one already.
 *
 * Return: 0 if a process keyring is now present; -errno on failure.
 */
static int install_process_keyring(void)
{
        struct cred *new;
        int ret;

        new = prepare_creds();
        if (!new)
                return -ENOMEM;

        ret = install_process_keyring_to_cred(new);
        if (ret < 0) {
                abort_creds(new);
                return ret;
        }

        return commit_creds(new);
}

/*
 * Install the given keyring as the session keyring of the given credentials
 * struct, replacing the existing one if any.  If the given keyring is NULL,
 * then install a new anonymous session keyring.
 * @cred can not be in use by any task yet.
 *
 * Return: 0 on success; -errno on failure.
 */
int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
{
        unsigned long flags;
        struct key *old;

        might_sleep();

        /* create an empty session keyring */
        if (!keyring) {
                flags = KEY_ALLOC_QUOTA_OVERRUN;
                if (cred->session_keyring)
                        flags = KEY_ALLOC_IN_QUOTA;

                keyring = keyring_alloc("_ses", cred->uid, cred->gid, cred,
                                        KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
                                        flags, NULL, NULL);
                if (IS_ERR(keyring))
                        return PTR_ERR(keyring);
        } else {
                __key_get(keyring);
        }

        /* install the keyring */
        old = cred->session_keyring;
        cred->session_keyring = keyring;

        if (old)
                key_put(old);

        return 0;
}

/*
 * Install the given keyring as the session keyring of the current task,
 * replacing the existing one if any.  If the given keyring is NULL, then
 * install a new anonymous session keyring.
 *
 * Return: 0 on success; -errno on failure.
 */
static int install_session_keyring(struct key *keyring)
{
        struct cred *new;
        int ret;

        new = prepare_creds();
        if (!new)
                return -ENOMEM;

        ret = install_session_keyring_to_cred(new, keyring);
        if (ret < 0) {
                abort_creds(new);
                return ret;
        }

        return commit_creds(new);
}

/*
 * Handle the fsuid changing.
 */
void key_fsuid_changed(struct cred *new_cred)
{
        /* update the ownership of the thread keyring */
        if (new_cred->thread_keyring) {
                down_write(&new_cred->thread_keyring->sem);
                new_cred->thread_keyring->uid = new_cred->fsuid;
                up_write(&new_cred->thread_keyring->sem);
        }
}

/*
 * Handle the fsgid changing.
 */
void key_fsgid_changed(struct cred *new_cred)
{
        /* update the ownership of the thread keyring */
        if (new_cred->thread_keyring) {
                down_write(&new_cred->thread_keyring->sem);
                new_cred->thread_keyring->gid = new_cred->fsgid;
                up_write(&new_cred->thread_keyring->sem);
        }
}

/*
 * Search the process keyrings attached to the supplied cred for the first
 * matching key under RCU conditions (the caller must be holding the RCU read
 * lock).
 *
 * The search criteria are the type and the match function.  The description is
 * given to the match function as a parameter, but doesn't otherwise influence
 * the search.  Typically the match function will compare the description
 * parameter to the key's description.
 *
 * This can only search keyrings that grant Search permission to the supplied
 * credentials.  Keyrings linked to searched keyrings will also be searched if
 * they grant Search permission too.  Keys can only be found if they grant
 * Search permission to the credentials.
 *
 * Returns a pointer to the key with the key usage count incremented if
 * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
 * matched negative keys.
 *
 * In the case of a successful return, the possession attribute is set on the
 * returned key reference.
 */
key_ref_t search_cred_keyrings_rcu(struct keyring_search_context *ctx)
{
        struct key *user_session;
        key_ref_t key_ref, ret, err;
        const struct cred *cred = ctx->cred;

        /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
         * searchable, but we failed to find a key or we found a negative key;
         * otherwise we want to return a sample error (probably -EACCES) if
         * none of the keyrings were searchable
         *
         * in terms of priority: success > -ENOKEY > -EAGAIN > other error
         */
        key_ref = NULL;
        ret = NULL;
        err = ERR_PTR(-EAGAIN);

        /* search the thread keyring first */
        if (cred->thread_keyring) {
                key_ref = keyring_search_rcu(
                        make_key_ref(cred->thread_keyring, 1), ctx);
                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                case -ENOKEY: /* negative key */
                        ret = key_ref;
                        break;
                default:
                        err = key_ref;
                        break;
                }
        }

        /* search the process keyring second */
        if (cred->process_keyring) {
                key_ref = keyring_search_rcu(
                        make_key_ref(cred->process_keyring, 1), ctx);
                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                        if (ret)
                                break;
                        fallthrough;
                case -ENOKEY: /* negative key */
                        ret = key_ref;
                        break;
                default:
                        err = key_ref;
                        break;
                }
        }

        /* search the session keyring */
        if (cred->session_keyring) {
                key_ref = keyring_search_rcu(
                        make_key_ref(cred->session_keyring, 1), ctx);

                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                        if (ret)
                                break;
                        fallthrough;
                case -ENOKEY: /* negative key */
                        ret = key_ref;
                        break;
                default:
                        err = key_ref;
                        break;
                }
        }
        /* or search the user-session keyring */
        else if ((user_session = get_user_session_keyring_rcu(cred))) {
                key_ref = keyring_search_rcu(make_key_ref(user_session, 1),
                                             ctx);
                key_put(user_session);

                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                        if (ret)
                                break;
                        fallthrough;
                case -ENOKEY: /* negative key */
                        ret = key_ref;
                        break;
                default:
                        err = key_ref;
                        break;
                }
        }

        /* no key - decide on the error we're going to go for */
        key_ref = ret ? ret : err;

found:
        return key_ref;
}

/*
 * Search the process keyrings attached to the supplied cred for the first
 * matching key in the manner of search_my_process_keyrings(), but also search
 * the keys attached to the assumed authorisation key using its credentials if
 * one is available.
 *
 * The caller must be holding the RCU read lock.
 *
 * Return same as search_cred_keyrings_rcu().
 */
key_ref_t search_process_keyrings_rcu(struct keyring_search_context *ctx)
{
        struct request_key_auth *rka;
        key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;

        key_ref = search_cred_keyrings_rcu(ctx);
        if (!IS_ERR(key_ref))
                goto found;
        err = key_ref;

        /* if this process has an instantiation authorisation key, then we also
         * search the keyrings of the process mentioned there
         * - we don't permit access to request_key auth keys via this method
         */
        if (ctx->cred->request_key_auth &&
            ctx->cred == current_cred() &&
            ctx->index_key.type != &key_type_request_key_auth
            ) {
                const struct cred *cred = ctx->cred;

                if (key_validate(cred->request_key_auth) == 0) {
                        rka = ctx->cred->request_key_auth->payload.data[0];

                        //// was search_process_keyrings() [ie. recursive]
                        ctx->cred = rka->cred;
                        key_ref = search_cred_keyrings_rcu(ctx);
                        ctx->cred = cred;

                        if (!IS_ERR(key_ref))
                                goto found;
                        ret = key_ref;
                }
        }

        /* no key - decide on the error we're going to go for */
        if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
                key_ref = ERR_PTR(-ENOKEY);
        else if (err == ERR_PTR(-EACCES))
                key_ref = ret;
        else
                key_ref = err;

found:
        return key_ref;
}
/*
 * See if the key we're looking at is the target key.
 */
bool lookup_user_key_possessed(const struct key *key,
                               const struct key_match_data *match_data)
{
        return key == match_data->raw_data;
}

/*
 * Look up a key ID given us by userspace with a given permissions mask to get
 * the key it refers to.
 *
 * Flags can be passed to request that special keyrings be created if referred
 * to directly, to permit partially constructed keys to be found and to skip
 * validity and permission checks on the found key.
 *
 * Returns a pointer to the key with an incremented usage count if successful;
 * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
 * to a key or the best found key was a negative key; -EKEYREVOKED or
 * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
 * found key doesn't grant the requested permit or the LSM denied access to it;
 * or -ENOMEM if a special keyring couldn't be created.
 *
 * In the case of a successful return, the possession attribute is set on the
 * returned key reference.
 */
key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
                          enum key_need_perm need_perm)
{
        struct keyring_search_context ctx = {
                .match_data.cmp         = lookup_user_key_possessed,
                .match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
                .flags                  = (KEYRING_SEARCH_NO_STATE_CHECK |
                                           KEYRING_SEARCH_RECURSE),
        };
        struct request_key_auth *rka;
        struct key *key, *user_session;
        key_ref_t key_ref, skey_ref;
        int ret;

try_again:
        ctx.cred = get_current_cred();
        key_ref = ERR_PTR(-ENOKEY);

        switch (id) {
        case KEY_SPEC_THREAD_KEYRING:
                if (!ctx.cred->thread_keyring) {
                        if (!(lflags & KEY_LOOKUP_CREATE))
                                goto error;

                        ret = install_thread_keyring();
                        if (ret < 0) {
                                key_ref = ERR_PTR(ret);
                                goto error;
                        }
                        goto reget_creds;
                }

                key = ctx.cred->thread_keyring;
                __key_get(key);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_PROCESS_KEYRING:
                if (!ctx.cred->process_keyring) {
                        if (!(lflags & KEY_LOOKUP_CREATE))
                                goto error;

                        ret = install_process_keyring();
                        if (ret < 0) {
                                key_ref = ERR_PTR(ret);
                                goto error;
                        }
                        goto reget_creds;
                }

                key = ctx.cred->process_keyring;
                __key_get(key);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_SESSION_KEYRING:
                if (!ctx.cred->session_keyring) {
                        /* always install a session keyring upon access if one
                         * doesn't exist yet */
                        ret = look_up_user_keyrings(NULL, &user_session);
                        if (ret < 0)
                                goto error;
                        if (lflags & KEY_LOOKUP_CREATE)
                                ret = join_session_keyring(NULL);
                        else
                                ret = install_session_keyring(user_session);

                        key_put(user_session);
                        if (ret < 0)
                                goto error;
                        goto reget_creds;
                } else if (test_bit(KEY_FLAG_UID_KEYRING,
                                    &ctx.cred->session_keyring->flags) &&
                           lflags & KEY_LOOKUP_CREATE) {
                        ret = join_session_keyring(NULL);
                        if (ret < 0)
                                goto error;
                        goto reget_creds;
                }

                key = ctx.cred->session_keyring;
                __key_get(key);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_USER_KEYRING:
                ret = look_up_user_keyrings(&key, NULL);
                if (ret < 0)
                        goto error;
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_USER_SESSION_KEYRING:
                ret = look_up_user_keyrings(NULL, &key);
                if (ret < 0)
                        goto error;
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_GROUP_KEYRING:
                /* group keyrings are not yet supported */
                key_ref = ERR_PTR(-EINVAL);
                goto error;

        case KEY_SPEC_REQKEY_AUTH_KEY:
                key = ctx.cred->request_key_auth;
                if (!key)
                        goto error;

                __key_get(key);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_REQUESTOR_KEYRING:
                if (!ctx.cred->request_key_auth)
                        goto error;

                down_read(&ctx.cred->request_key_auth->sem);
                if (test_bit(KEY_FLAG_REVOKED,
                             &ctx.cred->request_key_auth->flags)) {
                        key_ref = ERR_PTR(-EKEYREVOKED);
                        key = NULL;
                } else {
                        rka = ctx.cred->request_key_auth->payload.data[0];
                        key = rka->dest_keyring;
                        __key_get(key);
                }
                up_read(&ctx.cred->request_key_auth->sem);
                if (!key)
                        goto error;
                key_ref = make_key_ref(key, 1);
                break;

        default:
                key_ref = ERR_PTR(-EINVAL);
                if (id < 1)
                        goto error;

                key = key_lookup(id);
                if (IS_ERR(key)) {
                        key_ref = ERR_CAST(key);
                        goto error;
                }

                key_ref = make_key_ref(key, 0);

                /* check to see if we possess the key */
                ctx.index_key                   = key->index_key;
                ctx.match_data.raw_data         = key;
                kdebug("check possessed");
                rcu_read_lock();
                skey_ref = search_process_keyrings_rcu(&ctx);
                rcu_read_unlock();
                kdebug("possessed=%p", skey_ref);

                if (!IS_ERR(skey_ref)) {
                        key_put(key);
                        key_ref = skey_ref;
                }

                break;
        }

        /* unlink does not use the nominated key in any way, so can skip all
         * the permission checks as it is only concerned with the keyring */
        if (need_perm != KEY_NEED_UNLINK) {
                if (!(lflags & KEY_LOOKUP_PARTIAL)) {
                        ret = wait_for_key_construction(key, true);
                        switch (ret) {
                        case -ERESTARTSYS:
                                goto invalid_key;
                        default:
                                if (need_perm != KEY_AUTHTOKEN_OVERRIDE &&
                                    need_perm != KEY_DEFER_PERM_CHECK)
                                        goto invalid_key;
                        case 0:
                                break;
                        }
                } else if (need_perm != KEY_DEFER_PERM_CHECK) {
                        ret = key_validate(key);
                        if (ret < 0)
                                goto invalid_key;
                }

                ret = -EIO;
                if (!(lflags & KEY_LOOKUP_PARTIAL) &&
                    key_read_state(key) == KEY_IS_UNINSTANTIATED)
                        goto invalid_key;
        }

        /* check the permissions */
        ret = key_task_permission(key_ref, ctx.cred, need_perm);
        if (ret < 0)
                goto invalid_key;

        key->last_used_at = ktime_get_real_seconds();

error:
        put_cred(ctx.cred);
        return key_ref;

invalid_key:
        key_ref_put(key_ref);
        key_ref = ERR_PTR(ret);
        goto error;

        /* if we attempted to install a keyring, then it may have caused new
         * creds to be installed */
reget_creds:
        put_cred(ctx.cred);
        goto try_again;
}
EXPORT_SYMBOL(lookup_user_key);

/*
 * Join the named keyring as the session keyring if possible else attempt to
 * create a new one of that name and join that.
 *
 * If the name is NULL, an empty anonymous keyring will be installed as the
 * session keyring.
 *
 * Named session keyrings are joined with a semaphore held to prevent the
 * keyrings from going away whilst the attempt is made to going them and also
 * to prevent a race in creating compatible session keyrings.
 */
long join_session_keyring(const char *name)
{
        const struct cred *old;
        struct cred *new;
        struct key *keyring;
        long ret, serial;

        new = prepare_creds();
        if (!new)
                return -ENOMEM;
        old = current_cred();

        /* if no name is provided, install an anonymous keyring */
        if (!name) {
                ret = install_session_keyring_to_cred(new, NULL);
                if (ret < 0)
                        goto error;

                serial = new->session_keyring->serial;
                ret = commit_creds(new);
                if (ret == 0)
                        ret = serial;
                goto okay;
        }

        /* allow the user to join or create a named keyring */
        mutex_lock(&key_session_mutex);

        /* look for an existing keyring of this name */
        keyring = find_keyring_by_name(name, false);
        if (PTR_ERR(keyring) == -ENOKEY) {
                /* not found - try and create a new one */
                keyring = keyring_alloc(
                        name, old->uid, old->gid, old,
                        KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ | KEY_USR_LINK,
                        KEY_ALLOC_IN_QUOTA, NULL, NULL);
                if (IS_ERR(keyring)) {
                        ret = PTR_ERR(keyring);
                        goto error2;
                }
        } else if (IS_ERR(keyring)) {
                ret = PTR_ERR(keyring);
                goto error2;
        } else if (keyring == new->session_keyring) {
                ret = 0;
                goto error3;
        }

        /* we've got a keyring - now to install it */
        ret = install_session_keyring_to_cred(new, keyring);
        if (ret < 0)
                goto error3;

        commit_creds(new);
        mutex_unlock(&key_session_mutex);

        ret = keyring->serial;
        key_put(keyring);
okay:
        return ret;

error3:
        key_put(keyring);
error2:
        mutex_unlock(&key_session_mutex);
error:
        abort_creds(new);
        return ret;
}

/*
 * Replace a process's session keyring on behalf of one of its children when
 * the target  process is about to resume userspace execution.
 */
void key_change_session_keyring(struct callback_head *twork)
{
        const struct cred *old = current_cred();
        struct cred *new = container_of(twork, struct cred, rcu);

        if (unlikely(current->flags & PF_EXITING)) {
                put_cred(new);
                return;
        }

        new->  uid      = old->  uid;
        new-> euid      = old-> euid;
        new-> suid      = old-> suid;
        new->fsuid      = old->fsuid;
        new->  gid      = old->  gid;
        new-> egid      = old-> egid;
        new-> sgid      = old-> sgid;
        new->fsgid      = old->fsgid;
        new->user       = get_uid(old->user);
        new->user_ns    = get_user_ns(old->user_ns);
        new->group_info = get_group_info(old->group_info);

        new->securebits = old->securebits;
        new->cap_inheritable    = old->cap_inheritable;
        new->cap_permitted      = old->cap_permitted;
        new->cap_effective      = old->cap_effective;
        new->cap_ambient        = old->cap_ambient;
        new->cap_bset           = old->cap_bset;

        new->jit_keyring        = old->jit_keyring;
        new->thread_keyring     = key_get(old->thread_keyring);
        new->process_keyring    = key_get(old->process_keyring);

        security_transfer_creds(new, old);

        commit_creds(new);
}

/*
 * Make sure that root's user and user-session keyrings exist.
 */
static int __init init_root_keyring(void)
{
        return look_up_user_keyrings(NULL, NULL);
}

late_initcall(init_root_keyring);