KEYS: Make the session and process keyrings per-thread

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

/* Manage a process's keyrings
 *
 * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.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 <asm/uaccess.h>
#include "internal.h"

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

/* User keyring creation semaphore */
static DEFINE_MUTEX(key_user_keyring_mutex);

/* The root user's tracking struct */
struct key_user root_key_user = {
        .usage          = ATOMIC_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            = 0,
        .user_ns        = &init_user_ns,
};

/*
 * Install the user and user session keyrings for the current process's UID.
 */
int install_user_keyrings(void)
{
        struct user_struct *user;
        const struct cred *cred;
        struct key *uid_keyring, *session_keyring;
        char buf[20];
        int ret;

        cred = current_cred();
        user = cred->user;

        kenter("%p{%u}", user, user->uid);

        if (user->uid_keyring) {
                kleave(" = 0 [exist]");
                return 0;
        }

        mutex_lock(&key_user_keyring_mutex);
        ret = 0;

        if (!user->uid_keyring) {
                /* get the UID-specific keyring
                 * - 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 */
                sprintf(buf, "_uid.%u", user->uid);

                uid_keyring = find_keyring_by_name(buf, true);
                if (IS_ERR(uid_keyring)) {
                        uid_keyring = keyring_alloc(buf, user->uid, (gid_t) -1,
                                                    cred, KEY_ALLOC_IN_QUOTA,
                                                    NULL);
                        if (IS_ERR(uid_keyring)) {
                                ret = PTR_ERR(uid_keyring);
                                goto error;
                        }
                }

                /* get a default session keyring (which might also exist
                 * already) */
                sprintf(buf, "_uid_ses.%u", user->uid);

                session_keyring = find_keyring_by_name(buf, true);
                if (IS_ERR(session_keyring)) {
                        session_keyring =
                                keyring_alloc(buf, user->uid, (gid_t) -1,
                                              cred, KEY_ALLOC_IN_QUOTA, 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_both;
                }

                /* install the keyrings */
                user->uid_keyring = uid_keyring;
                user->session_keyring = session_keyring;
        }

        mutex_unlock(&key_user_keyring_mutex);
        kleave(" = 0");
        return 0;

error_release_both:
        key_put(session_keyring);
error_release:
        key_put(uid_keyring);
error:
        mutex_unlock(&key_user_keyring_mutex);
        kleave(" = %d", ret);
        return ret;
}

/*
 * Install a fresh thread keyring directly to new credentials.  This keyring is
 * allowed to overrun the quota.
 */
int install_thread_keyring_to_cred(struct cred *new)
{
        struct key *keyring;

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

        new->thread_keyring = keyring;
        return 0;
}

/*
 * Install a fresh thread keyring, discarding the old one.
 */
static int install_thread_keyring(void)
{
        struct cred *new;
        int ret;

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

        BUG_ON(new->thread_keyring);

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

        return commit_creds(new);
}

/*
 * Install a process keyring directly to a credentials struct.
 *
 * Returns -EEXIST if there was already a process keyring, 0 if one installed,
 * and other value on any other error
 */
int install_process_keyring_to_cred(struct cred *new)
{
        struct key *keyring;

        if (new->process_keyring)
                return -EEXIST;

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

        new->process_keyring = keyring;
        return 0;
}

/*
 * Make sure a process keyring is installed for the current process.  The
 * existing process keyring is not replaced.
 *
 * Returns 0 if there is a process keyring by the end of this function, some
 * error otherwise.
 */
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 != -EEXIST ? ret : 0;
        }

        return commit_creds(new);
}

/*
 * Install a session keyring directly to a credentials struct.
 */
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, flags, NULL);
                if (IS_ERR(keyring))
                        return PTR_ERR(keyring);
        } else {
                atomic_inc(&keyring->usage);
        }

        /* install the keyring */
        old = cred->session_keyring;
        rcu_assign_pointer(cred->session_keyring, keyring);

        if (old)
                key_put(old);

        return 0;
}

/*
 * Install a session keyring, discarding the old one.  If a keyring is not
 * supplied, an empty one is invented.
 */
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 task_struct *tsk)
{
        /* update the ownership of the thread keyring */
        BUG_ON(!tsk->cred);
        if (tsk->cred->thread_keyring) {
                down_write(&tsk->cred->thread_keyring->sem);
                tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
                up_write(&tsk->cred->thread_keyring->sem);
        }
}

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

/*
 * Search the process keyrings attached to the supplied cred for the first
 * matching key.
 *
 * 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_my_process_keyrings(struct key_type *type,
                                     const void *description,
                                     key_match_func_t match,
                                     bool no_state_check,
                                     const struct cred *cred)
{
        key_ref_t key_ref, ret, err;

        /* 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_aux(
                        make_key_ref(cred->thread_keyring, 1),
                        cred, type, description, match, no_state_check);
                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_aux(
                        make_key_ref(cred->process_keyring, 1),
                        cred, type, description, match, no_state_check);
                if (!IS_ERR(key_ref))
                        goto found;

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

        /* search the session keyring */
        if (cred->session_keyring) {
                rcu_read_lock();
                key_ref = keyring_search_aux(
                        make_key_ref(rcu_dereference(cred->session_keyring), 1),
                        cred, type, description, match, no_state_check);
                rcu_read_unlock();

                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                        if (ret)
                                break;
                case -ENOKEY: /* negative key */
                        ret = key_ref;
                        break;
                default:
                        err = key_ref;
                        break;
                }
        }
        /* or search the user-session keyring */
        else if (cred->user->session_keyring) {
                key_ref = keyring_search_aux(
                        make_key_ref(cred->user->session_keyring, 1),
                        cred, type, description, match, no_state_check);
                if (!IS_ERR(key_ref))
                        goto found;

                switch (PTR_ERR(key_ref)) {
                case -EAGAIN: /* no key */
                        if (ret)
                                break;
                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.
 *
 * Return same as search_my_process_keyrings().
 */
key_ref_t search_process_keyrings(struct key_type *type,
                                  const void *description,
                                  key_match_func_t match,
                                  const struct cred *cred)
{
        struct request_key_auth *rka;
        key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;

        might_sleep();

        key_ref = search_my_process_keyrings(type, description, match,
                                             false, cred);
        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 (cred->request_key_auth &&
            cred == current_cred() &&
            type != &key_type_request_key_auth
            ) {
                /* defend against the auth key being revoked */
                down_read(&cred->request_key_auth->sem);

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

                        key_ref = search_process_keyrings(type, description,
                                                          match, rka->cred);

                        up_read(&cred->request_key_auth->sem);

                        if (!IS_ERR(key_ref))
                                goto found;

                        ret = key_ref;
                } else {
                        up_read(&cred->request_key_auth->sem);
                }
        }

        /* 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.
 */
int lookup_user_key_possessed(const struct key *key, const void *target)
{
        return key == target;
}

/*
 * 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,
                          key_perm_t perm)
{
        struct request_key_auth *rka;
        const struct cred *cred;
        struct key *key;
        key_ref_t key_ref, skey_ref;
        int ret;

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

        switch (id) {
        case KEY_SPEC_THREAD_KEYRING:
                if (!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 = cred->thread_keyring;
                atomic_inc(&key->usage);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_PROCESS_KEYRING:
                if (!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 = cred->process_keyring;
                atomic_inc(&key->usage);
                key_ref = make_key_ref(key, 1);
                break;

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

                        if (ret < 0)
                                goto error;
                        goto reget_creds;
                } else if (cred->session_keyring ==
                           cred->user->session_keyring &&
                           lflags & KEY_LOOKUP_CREATE) {
                        ret = join_session_keyring(NULL);
                        if (ret < 0)
                                goto error;
                        goto reget_creds;
                }

                rcu_read_lock();
                key = rcu_dereference(cred->session_keyring);
                atomic_inc(&key->usage);
                rcu_read_unlock();
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_USER_KEYRING:
                if (!cred->user->uid_keyring) {
                        ret = install_user_keyrings();
                        if (ret < 0)
                                goto error;
                }

                key = cred->user->uid_keyring;
                atomic_inc(&key->usage);
                key_ref = make_key_ref(key, 1);
                break;

        case KEY_SPEC_USER_SESSION_KEYRING:
                if (!cred->user->session_keyring) {
                        ret = install_user_keyrings();
                        if (ret < 0)
                                goto error;
                }

                key = cred->user->session_keyring;
                atomic_inc(&key->usage);
                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 = cred->request_key_auth;
                if (!key)
                        goto error;

                atomic_inc(&key->usage);
                key_ref = make_key_ref(key, 1);
                break;

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

                down_read(&cred->request_key_auth->sem);
                if (test_bit(KEY_FLAG_REVOKED,
                             &cred->request_key_auth->flags)) {
                        key_ref = ERR_PTR(-EKEYREVOKED);
                        key = NULL;
                } else {
                        rka = cred->request_key_auth->payload.data;
                        key = rka->dest_keyring;
                        atomic_inc(&key->usage);
                }
                up_read(&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 */
                skey_ref = search_process_keyrings(key->type, key,
                                                   lookup_user_key_possessed,
                                                   cred);

                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 (lflags & KEY_LOOKUP_FOR_UNLINK) {
                ret = 0;
                goto error;
        }

        if (!(lflags & KEY_LOOKUP_PARTIAL)) {
                ret = wait_for_key_construction(key, true);
                switch (ret) {
                case -ERESTARTSYS:
                        goto invalid_key;
                default:
                        if (perm)
                                goto invalid_key;
                case 0:
                        break;
                }
        } else if (perm) {
                ret = key_validate(key);
                if (ret < 0)
                        goto invalid_key;
        }

        ret = -EIO;
        if (!(lflags & KEY_LOOKUP_PARTIAL) &&
            !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
                goto invalid_key;

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

        key->last_used_at = current_kernel_time().tv_sec;

error:
        put_cred(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(cred);
        goto try_again;
}

/*
 * 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_ALLOC_IN_QUOTA, 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 error2;
        }

        /* we've got a keyring - now to install it */
        ret = install_session_keyring_to_cred(new, keyring);
        if (ret < 0)
                goto error2;

        commit_creds(new);
        mutex_unlock(&key_session_mutex);

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

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(new->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_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);
}