request_key.c

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/* Request a key from userspace
 *
 * Copyright (C) 2004-2007 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/kmod.h>
#include <linux/err.h>
#include <linux/keyctl.h>
#include <linux/slab.h>
#include "internal.h"

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

/*
 * wait_on_bit() sleep function for uninterruptible waiting
 */
static int key_wait_bit(void *flags)
{
    schedule();
    return 0;
}

/*
 * wait_on_bit() sleep function for interruptible waiting
 */
static int key_wait_bit_intr(void *flags)
{
    schedule();
    return signal_pending(current) ? -ERESTARTSYS : 0;
}

void complete_request_key(struct key_construction *cons, int error)
{
    kenter("{%d,%d},%d", cons->key->serial, cons->authkey->serial, error);

    if (error < 0)
        key_negate_and_link(cons->key, key_negative_timeout, NULL,
                    cons->authkey);
    else
        key_revoke(cons->authkey);

    key_put(cons->key);
    key_put(cons->authkey);
    kfree(cons);
}
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(char *path, char **argv, char **envp,
                    struct key *session_keyring, int wait)
{
    return call_usermodehelper_fns(path, argv, envp, wait,
                       umh_keys_init, umh_keys_cleanup,
                       key_get(session_keyring));
}

/*
 * 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_construction *cons,
                 const char *op,
                 void *aux)
{
    const struct cred *cred = current_cred();
    key_serial_t prkey, sskey;
    struct key *key = cons->key, *authkey = cons->authkey, *keyring,
        *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, op);

    ret = install_user_keyrings();
    if (ret < 0)
        goto error_alloc;

    /* 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_ALLOC_QUOTA_OVERRUN, 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->tgcred->process_keyring)
        prkey = cred->tgcred->process_keyring->serial;
    sprintf(keyring_str[1], "%d", prkey);

    rcu_read_lock();
    session = rcu_dereference(cred->tgcred->session_keyring);
    if (!session)
        session = cred->user->session_keyring;
    sskey = session->serial;
    rcu_read_unlock();

    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++] = "/sbin/request-key";
    argv[i++] = (char *) 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(argv[0], 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:
    complete_request_key(cons, 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)
{
    struct key_construction *cons;
    request_key_actor_t actor;
    struct key *authkey;
    int ret;

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

    cons = kmalloc(sizeof(*cons), GFP_KERNEL);
    if (!cons)
        return -ENOMEM;

    /* allocate an authorisation key */
    authkey = request_key_auth_new(key, callout_info, callout_len,
                       dest_keyring);
    if (IS_ERR(authkey)) {
        kfree(cons);
        ret = PTR_ERR(authkey);
        authkey = NULL;
    } else {
        cons->authkey = key_get(authkey);
        cons->key = key_get(key);

        /* make the call */
        actor = call_sbin_request_key;
        if (key->type->request_key)
            actor = key->type->request_key;

        ret = actor(cons, "create", aux);

        /* check that the actor called complete_request_key() prior to
         * returning an error */
        WARN_ON(ret < 0 &&
            !test_bit(KEY_FLAG_REVOKED, &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 void 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;

    kenter("%p", dest_keyring);

    /* find the appropriate keyring */
    if (dest_keyring) {
        /* the caller supplied one */
        key_get(dest_keyring);
    } else {
        /* 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 = authkey->payload.data;
                if (!test_bit(KEY_FLAG_REVOKED,
                          &authkey->flags))
                    dest_keyring =
                        key_get(rka->dest_keyring);
                up_read(&authkey->sem);
                if (dest_keyring)
                    break;
            }

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

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

        case KEY_REQKEY_DEFL_SESSION_KEYRING:
            rcu_read_lock();
            dest_keyring = key_get(
                rcu_dereference(cred->tgcred->session_keyring));
            rcu_read_unlock();

            if (dest_keyring)
                break;

        case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
            dest_keyring =
                key_get(cred->user->session_keyring);
            break;

        case KEY_REQKEY_DEFL_USER_KEYRING:
            dest_keyring = key_get(cred->user->uid_keyring);
            break;

        case KEY_REQKEY_DEFL_GROUP_KEYRING:
        default:
            BUG();
        }
    }

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

/*
 * 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 key_type *type,
                   const char *description,
                   struct key *dest_keyring,
                   unsigned long flags,
                   struct key_user *user,
                   struct key **_key)
{
    const struct cred *cred = current_cred();
    unsigned long prealloc;
    struct key *key;
    key_ref_t key_ref;
    int ret;

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

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

    key = key_alloc(type, description, cred->fsuid, cred->fsgid, cred,
            KEY_POS_ALL, flags);
    if (IS_ERR(key))
        goto alloc_failed;

    set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);

    if (dest_keyring) {
        ret = __key_link_begin(dest_keyring, type, description,
                       &prealloc);
        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);

    key_ref = search_process_keyrings(type, description, type->match, cred);
    if (!IS_ERR(key_ref))
        goto key_already_present;

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

    mutex_unlock(&key_construction_mutex);
    if (dest_keyring)
        __key_link_end(dest_keyring, type, prealloc);
    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, &prealloc);
        __key_link_end(dest_keyring, type, prealloc);
        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:
    mutex_unlock(&user->cons_lock);
    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 key_type *type,
                      const char *description,
                      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("");

    user = key_user_lookup(current_fsuid());
    if (!user)
        return ERR_PTR(-ENOMEM);

    construct_get_dest_keyring(&dest_keyring);

    ret = construct_alloc_key(type, description, 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 couldnt_alloc_key;
    }

    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);
couldnt_alloc_key:
    key_put(dest_keyring);
    kleave(" = %d", ret);
    return ERR_PTR(ret);
}

struct key *request_key_and_link(struct key_type *type,
                 const char *description,
                 const void *callout_info,
                 size_t callout_len,
                 void *aux,
                 struct key *dest_keyring,
                 unsigned long flags)
{
    const struct cred *cred = current_cred();
    struct key *key;
    key_ref_t key_ref;
    int ret;

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

    /* search all the process keyrings for a key */
    key_ref = search_process_keyrings(type, description, type->match, cred);

    if (!IS_ERR(key_ref)) {
        key = key_ref_to_ptr(key_ref);
        if (dest_keyring) {
            construct_get_dest_keyring(&dest_keyring);
            ret = key_link(dest_keyring, key);
            key_put(dest_keyring);
            if (ret < 0) {
                key_put(key);
                key = ERR_PTR(ret);
                goto error;
            }
        }
    } 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;

        key = construct_key_and_link(type, description, callout_info,
                         callout_len, aux, dest_keyring,
                         flags);
    }

error:
    kleave(" = %p", key);
    return key;
}

int wait_for_key_construction(struct key *key, bool intr)
{
    int ret;

    ret = wait_on_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT,
              intr ? key_wait_bit_intr : key_wait_bit,
              intr ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
    if (ret < 0)
        return ret;
    if (test_bit(KEY_FLAG_NEGATIVE, &key->flags))
        return key->type_data.reject_error;
    return key_validate(key);
}
EXPORT_SYMBOL(wait_for_key_construction);

struct key *request_key(struct key_type *type,
            const char *description,
            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, 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);

struct key *request_key_with_auxdata(struct key_type *type,
                     const char *description,
                     const void *callout_info,
                     size_t callout_len,
                     void *aux)
{
    struct key *key;
    int ret;

    key = request_key_and_link(type, description, 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_async - Request a key (allow async construction)
 * @type: Type of key.
 * @description: The searchable description of the key.
 * @callout_info: The data to pass to the instantiation upcall (or NULL).
 * @callout_len: The length of callout_info.
 *
 * 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 and
 * no auxiliary data can be passed.
 *
 * The caller should call wait_for_key_construction() to wait for the
 * completion of the returned key if it is still undergoing construction.
 */
struct key *request_key_async(struct key_type *type,
                  const char *description,
                  const void *callout_info,
                  size_t callout_len)
{
    return request_key_and_link(type, description, callout_info,
                    callout_len, NULL, NULL,
                    KEY_ALLOC_IN_QUOTA);
}
EXPORT_SYMBOL(request_key_async);

/*
 * request a key with auxiliary data for the upcaller (allow async construction)
 * @type: Type of key.
 * @description: The searchable description of the key.
 * @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.
 *
 * The caller should call wait_for_key_construction() to wait for the
 * completion of the returned key if it is still undergoing construction.
 */
struct key *request_key_async_with_auxdata(struct key_type *type,
                       const char *description,
                       const void *callout_info,
                       size_t callout_len,
                       void *aux)
{
    return request_key_and_link(type, description, callout_info,
                    callout_len, aux, NULL, KEY_ALLOC_IN_QUOTA);
}
EXPORT_SYMBOL(request_key_async_with_auxdata);