request_key_auth.c

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/* Request key authorisation token key definition.
 *
 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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.txt
 */

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include "internal.h"

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),
    .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,
};

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

    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;
    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;

    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;

    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;
        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);
    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, atomic_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);
}

/*
 * See if an authorisation key is associated with a particular key.
 */
static int key_get_instantiation_authkey_match(const struct key *key,
                           const void *_id)
{
    struct request_key_auth *rka = key->payload.data;
    key_serial_t id = (key_serial_t)(unsigned long) _id;

    return rka->target_key->serial == id;
}

/*
 * 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)
{
    const struct cred *cred = current_cred();
    struct key *authkey;
    key_ref_t authkey_ref;

    authkey_ref = search_process_keyrings(
        &key_type_request_key_auth,
        (void *) (unsigned long) target_id,
        key_get_instantiation_authkey_match,
        cred);

    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;
}