/* Request key authorisation token key definition.
 *
 * Copyright (C) 2005 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.
 *
 * See Documentation/security/keys/request-key.rst
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include "internal.h"
#include <keys/user-type.h>

static int request_key_auth_preparse(struct key_preparsed_payload *);
static void request_key_auth_free_preparse(struct key_preparsed_payload *);
static int request_key_auth_instantiate(struct key *,
                                        struct key_preparsed_payload *);
static void request_key_auth_describe(const struct key *, struct seq_file *);
static void request_key_auth_revoke(struct key *);
static void request_key_auth_destroy(struct key *);
static long request_key_auth_read(const struct key *, char __user *, size_t);

/*
 * The request-key authorisation key type definition.
 */
struct key_type key_type_request_key_auth = {
        .name           = ".request_key_auth",
        .def_datalen    = sizeof(struct request_key_auth),
        .preparse       = request_key_auth_preparse,
        .free_preparse  = request_key_auth_free_preparse,
        .instantiate    = request_key_auth_instantiate,
        .describe       = request_key_auth_describe,
        .revoke         = request_key_auth_revoke,
        .destroy        = request_key_auth_destroy,
        .read           = request_key_auth_read,
};

static int request_key_auth_preparse(struct key_preparsed_payload *prep)
{
        return 0;
}

static void request_key_auth_free_preparse(struct key_preparsed_payload *prep)
{
}

/*
 * Instantiate a request-key authorisation key.
 */
static int request_key_auth_instantiate(struct key *key,
                                        struct key_preparsed_payload *prep)
{
        key->payload.data[0] = (struct request_key_auth *)prep->data;
        return 0;
}

/*
 * Describe an authorisation token.
 */
static void request_key_auth_describe(const struct key *key,
                                      struct seq_file *m)
{
        struct request_key_auth *rka = key->payload.data[0];

        seq_puts(m, "key:");
        seq_puts(m, key->description);
        if (key_is_instantiated(key))
                seq_printf(m, " pid:%d ci:%zu", rka->pid, rka->callout_len);
}

/*
 * Read the callout_info data (retrieves the callout information).
 * - the key's semaphore is read-locked
 */
static long request_key_auth_read(const struct key *key,
                                  char __user *buffer, size_t buflen)
{
        struct request_key_auth *rka = key->payload.data[0];
        size_t datalen;
        long ret;

        datalen = rka->callout_len;
        ret = datalen;

        /* we can return the data as is */
        if (buffer && buflen > 0) {
                if (buflen > datalen)
                        buflen = datalen;

                if (copy_to_user(buffer, rka->callout_info, buflen) != 0)
                        ret = -EFAULT;
        }

        return ret;
}

/*
 * Handle revocation of an authorisation token key.
 *
 * Called with the key sem write-locked.
 */
static void request_key_auth_revoke(struct key *key)
{
        struct request_key_auth *rka = key->payload.data[0];

        kenter("{%d}", key->serial);

        if (rka->cred) {
                put_cred(rka->cred);
                rka->cred = NULL;
        }
}

/*
 * Destroy an instantiation authorisation token key.
 */
static void request_key_auth_destroy(struct key *key)
{
        struct request_key_auth *rka = key->payload.data[0];

        kenter("{%d}", key->serial);

        if (rka->cred) {
                put_cred(rka->cred);
                rka->cred = NULL;
        }

        key_put(rka->target_key);
        key_put(rka->dest_keyring);
        kfree(rka->callout_info);
        kfree(rka);
}

/*
 * Create an authorisation token for /sbin/request-key or whoever to gain
 * access to the caller's security data.
 */
struct key *request_key_auth_new(struct key *target, const void *callout_info,
                                 size_t callout_len, struct key *dest_keyring)
{
        struct request_key_auth *rka, *irka;
        const struct cred *cred = current->cred;
        struct key *authkey = NULL;
        char desc[20];
        int ret;

        kenter("%d,", target->serial);

        /* allocate a auth record */
        rka = kmalloc(sizeof(*rka), GFP_KERNEL);
        if (!rka) {
                kleave(" = -ENOMEM");
                return ERR_PTR(-ENOMEM);
        }
        rka->callout_info = kmalloc(callout_len, GFP_KERNEL);
        if (!rka->callout_info) {
                kleave(" = -ENOMEM");
                kfree(rka);
                return ERR_PTR(-ENOMEM);
        }

        /* see if the calling process is already servicing the key request of
         * another process */
        if (cred->request_key_auth) {
                /* it is - use that instantiation context here too */
                down_read(&cred->request_key_auth->sem);

                /* if the auth key has been revoked, then the key we're
                 * servicing is already instantiated */
                if (test_bit(KEY_FLAG_REVOKED, &cred->request_key_auth->flags))
                        goto auth_key_revoked;

                irka = cred->request_key_auth->payload.data[0];
                rka->cred = get_cred(irka->cred);
                rka->pid = irka->pid;

                up_read(&cred->request_key_auth->sem);
        }
        else {
                /* it isn't - use this process as the context */
                rka->cred = get_cred(cred);
                rka->pid = current->pid;
        }

        rka->target_key = key_get(target);
        rka->dest_keyring = key_get(dest_keyring);
        memcpy(rka->callout_info, callout_info, callout_len);
        rka->callout_len = callout_len;

        /* allocate the auth key */
        sprintf(desc, "%x", target->serial);

        authkey = key_alloc(&key_type_request_key_auth, desc,
                            cred->fsuid, cred->fsgid, cred,
                            KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
                            KEY_USR_VIEW, KEY_ALLOC_NOT_IN_QUOTA, NULL);
        if (IS_ERR(authkey)) {
                ret = PTR_ERR(authkey);
                goto error_alloc;
        }

        /* construct the auth key */
        ret = key_instantiate_and_link(authkey, rka, 0, NULL, NULL);
        if (ret < 0)
                goto error_inst;

        kleave(" = {%d,%d}", authkey->serial, refcount_read(&authkey->usage));
        return authkey;

auth_key_revoked:
        up_read(&cred->request_key_auth->sem);
        kfree(rka->callout_info);
        kfree(rka);
        kleave("= -EKEYREVOKED");
        return ERR_PTR(-EKEYREVOKED);

error_inst:
        key_revoke(authkey);
        key_put(authkey);
error_alloc:
        key_put(rka->target_key);
        key_put(rka->dest_keyring);
        kfree(rka->callout_info);
        kfree(rka);
        kleave("= %d", ret);
        return ERR_PTR(ret);
}

/*
 * Search the current process's keyrings for the authorisation key for
 * instantiation of a key.
 */
struct key *key_get_instantiation_authkey(key_serial_t target_id)
{
        char description[16];
        struct keyring_search_context ctx = {
                .index_key.type         = &key_type_request_key_auth,
                .index_key.description  = 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,
        };
        struct key *authkey;
        key_ref_t authkey_ref;

        sprintf(description, "%x", target_id);

        authkey_ref = search_process_keyrings(&ctx);

        if (IS_ERR(authkey_ref)) {
                authkey = ERR_CAST(authkey_ref);
                if (authkey == ERR_PTR(-EAGAIN))
                        authkey = ERR_PTR(-ENOKEY);
                goto error;
        }

        authkey = key_ref_to_ptr(authkey_ref);
        if (test_bit(KEY_FLAG_REVOKED, &authkey->flags)) {
                key_put(authkey);
                authkey = ERR_PTR(-EKEYREVOKED);
        }

error:
        return authkey;
}