modules/session/mod_session_crypto.c

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "mod_session.h"
#include "apu_version.h"
#include "apr_base64.h"                /* for apr_base64_decode et al */
#include "apr_lib.h"
#include "apr_strings.h"
#include "http_log.h"
#include "http_core.h"

#if APU_MAJOR_VERSION == 1 && APU_MINOR_VERSION < 4

#error session_crypto_module requires APU v1.4.0 or later

#elif APU_HAVE_CRYPTO == 0

#error Crypto support must be enabled in APR

#else

#include "apr_crypto.h"                /* for apr_*_crypt et al */

#define CRYPTO_KEY "session_crypto_context"

module AP_MODULE_DECLARE_DATA session_crypto_module;

/**
 * Structure to carry the per-dir session config.
 */
typedef struct {
    apr_array_header_t *passphrases;
    int passphrases_set;
    const char *cipher;
    int cipher_set;
} session_crypto_dir_conf;

/**
 * Structure to carry the server wide session config.
 */
typedef struct {
    const char *library;
    const char *params;
    int library_set;
} session_crypto_conf;

/**
 * Initialise the encryption as per the current config.
 *
 * Returns APR_SUCCESS if successful.
 */
static apr_status_t crypt_init(request_rec *r,
        const apr_crypto_t *f, apr_crypto_block_key_type_e **cipher,
        session_crypto_dir_conf * dconf)
{
    apr_status_t res;
    apr_hash_t *ciphers;

    res = apr_crypto_get_block_key_types(&ciphers, f);
    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01823)
                "no ciphers returned by APR. "
                "session encryption not possible");
        return res;
    }

    *cipher = apr_hash_get(ciphers, dconf->cipher, APR_HASH_KEY_STRING);
    if (!(*cipher)) {
        apr_hash_index_t *hi;
        const void *key;
        apr_ssize_t klen;
        int sum = 0;
        int offset = 0;
        char *options = NULL;

        for (hi = apr_hash_first(r->pool, ciphers); hi; hi = apr_hash_next(hi)) {
            apr_hash_this(hi, NULL, &klen, NULL);
            sum += klen + 2;
        }
        for (hi = apr_hash_first(r->pool, ciphers); hi; hi = apr_hash_next(hi)) {
            apr_hash_this(hi, &key, &klen, NULL);
            if (!options) {
                options = apr_palloc(r->pool, sum + 1);
            }
            else {
                options[offset++] = ',';
                options[offset++] = ' ';
            }
            strncpy(options + offset, key, klen);
            offset += klen;
        }
        options[offset] = 0;

        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01824)
                "cipher '%s' not recognised by crypto driver. "
                "session encryption not possible, options: %s", dconf->cipher, options);

        return APR_EGENERAL;
    }

    return APR_SUCCESS;
}

/**
 * Encrypt the string given as per the current config.
 *
 * Returns APR_SUCCESS if successful.
 */
static apr_status_t encrypt_string(request_rec * r, const apr_crypto_t *f,
        session_crypto_dir_conf *dconf, const char *in, char **out)
{
    apr_status_t res;
    apr_crypto_key_t *key = NULL;
    apr_size_t ivSize = 0;
    apr_crypto_block_t *block = NULL;
    unsigned char *encrypt = NULL;
    unsigned char *combined = NULL;
    apr_size_t encryptlen, tlen;
    char *base64;
    apr_size_t blockSize = 0;
    const unsigned char *iv = NULL;
    apr_uuid_t salt;
    apr_crypto_block_key_type_e *cipher;
    const char *passphrase;

    /* by default, return an empty string */
    *out = "";

    /* don't attempt to encrypt an empty string, trying to do so causes a segfault */
    if (!in || !*in) {
        return APR_SUCCESS;
    }

    /* use a uuid as a salt value, and prepend it to our result */
    apr_uuid_get(&salt);
    res = crypt_init(r, f, &cipher, dconf);
    if (res != APR_SUCCESS) {
        return res;
    }

    /* encrypt using the first passphrase in the list */
    passphrase = APR_ARRAY_IDX(dconf->passphrases, 0, char *);
    res = apr_crypto_passphrase(&key, &ivSize, passphrase,
            strlen(passphrase),
            (unsigned char *) (&salt), sizeof(apr_uuid_t),
            *cipher, APR_MODE_CBC, 1, 4096, f, r->pool);
    if (APR_STATUS_IS_ENOKEY(res)) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01825)
                "the passphrase '%s' was empty", passphrase);
    }
    if (APR_STATUS_IS_EPADDING(res)) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01826)
                "padding is not supported for cipher");
    }
    if (APR_STATUS_IS_EKEYTYPE(res)) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01827)
                "the key type is not known");
    }
    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01828)
                "encryption could not be configured.");
        return res;
    }

    res = apr_crypto_block_encrypt_init(&block, &iv, key, &blockSize, r->pool);
    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01829)
                "apr_crypto_block_encrypt_init failed");
        return res;
    }

    /* encrypt the given string */
    res = apr_crypto_block_encrypt(&encrypt, &encryptlen, (unsigned char *)in,
            strlen(in), block);
    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01830)
                "apr_crypto_block_encrypt failed");
        return res;
    }
    res = apr_crypto_block_encrypt_finish(encrypt + encryptlen, &tlen, block);
    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01831)
                "apr_crypto_block_encrypt_finish failed");
        return res;
    }
    encryptlen += tlen;

    /* prepend the salt and the iv to the result */
    combined = apr_palloc(r->pool, ivSize + encryptlen + sizeof(apr_uuid_t));
    memcpy(combined, &salt, sizeof(apr_uuid_t));
    memcpy(combined + sizeof(apr_uuid_t), iv, ivSize);
    memcpy(combined + sizeof(apr_uuid_t) + ivSize, encrypt, encryptlen);

    /* base64 encode the result */
    base64 = apr_palloc(r->pool, apr_base64_encode_len(ivSize + encryptlen +
                    sizeof(apr_uuid_t) + 1)
            * sizeof(char));
    apr_base64_encode(base64, (const char *) combined,
            ivSize + encryptlen + sizeof(apr_uuid_t));
    *out = base64;

    return res;

}

/**
 * Decrypt the string given as per the current config.
 *
 * Returns APR_SUCCESS if successful.
 */
static apr_status_t decrypt_string(request_rec * r, const apr_crypto_t *f,
        session_crypto_dir_conf *dconf, const char *in, char **out)
{
    apr_status_t res;
    apr_crypto_key_t *key = NULL;
    apr_size_t ivSize = 0;
    apr_crypto_block_t *block = NULL;
    unsigned char *decrypted = NULL;
    apr_size_t decryptedlen, tlen;
    apr_size_t decodedlen;
    char *decoded;
    apr_size_t blockSize = 0;
    apr_crypto_block_key_type_e *cipher;
    int i = 0;

    /* strip base64 from the string */
    decoded = apr_palloc(r->pool, apr_base64_decode_len(in));
    decodedlen = apr_base64_decode(decoded, in);
    decoded[decodedlen] = '\0';

    res = crypt_init(r, f, &cipher, dconf);
    if (res != APR_SUCCESS) {
        return res;
    }

    /* try each passphrase in turn */
    for (; i < dconf->passphrases->nelts; i++) {
        const char *passphrase = APR_ARRAY_IDX(dconf->passphrases, i, char *);
        apr_size_t len = decodedlen;
        char *slider = decoded;

        /* encrypt using the first passphrase in the list */
        res = apr_crypto_passphrase(&key, &ivSize, passphrase,
                strlen(passphrase),
                (unsigned char *)decoded, sizeof(apr_uuid_t),
                *cipher, APR_MODE_CBC, 1, 4096, f, r->pool);
        if (APR_STATUS_IS_ENOKEY(res)) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01832)
                    "the passphrase '%s' was empty", passphrase);
            continue;
        }
        else if (APR_STATUS_IS_EPADDING(res)) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01833)
                    "padding is not supported for cipher");
            continue;
        }
        else if (APR_STATUS_IS_EKEYTYPE(res)) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01834)
                    "the key type is not known");
            continue;
        }
        else if (APR_SUCCESS != res) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01835)
                    "encryption could not be configured.");
            continue;
        }

        /* sanity check - decoded too short? */
        if (decodedlen < (sizeof(apr_uuid_t) + ivSize)) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r, APLOGNO(01836)
                    "too short to decrypt, skipping");
            res = APR_ECRYPT;
            continue;
        }

        /* bypass the salt at the start of the decoded block */
        slider += sizeof(apr_uuid_t);
        len -= sizeof(apr_uuid_t);

        res = apr_crypto_block_decrypt_init(&block, &blockSize, (unsigned char *)slider, key,
                r->pool);
        if (APR_SUCCESS != res) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01837)
                    "apr_crypto_block_decrypt_init failed");
            continue;
        }

        /* bypass the iv at the start of the decoded block */
        slider += ivSize;
        len -= ivSize;

        /* decrypt the given string */
        res = apr_crypto_block_decrypt(&decrypted, &decryptedlen,
                (unsigned char *)slider, len, block);
        if (res) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01838)
                    "apr_crypto_block_decrypt failed");
            continue;
        }
        *out = (char *) decrypted;

        res = apr_crypto_block_decrypt_finish(decrypted + decryptedlen, &tlen, block);
        if (APR_SUCCESS != res) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01839)
                    "apr_crypto_block_decrypt_finish failed");
            continue;
        }
        decryptedlen += tlen;
        decrypted[decryptedlen] = 0;

        break;
    }

    if (APR_SUCCESS != res) {
        ap_log_rerror(APLOG_MARK, APLOG_INFO, res, r, APLOGNO(01840)
                "decryption failed");
    }

    return res;

}

/**
 * Crypto encoding for the session.
 *
 * @param r The request pointer.
 * @param z A pointer to where the session will be written.
 */
static apr_status_t session_crypto_encode(request_rec * r, session_rec * z)
{

    char *encoded = NULL;
    apr_status_t res;
    const apr_crypto_t *f = NULL;
    session_crypto_dir_conf *dconf = ap_get_module_config(r->per_dir_config,
            &session_crypto_module);

    if (dconf->passphrases_set && z->encoded && *z->encoded) {
        apr_pool_userdata_get((void **)&f, CRYPTO_KEY, r->server->process->pconf);
        res = encrypt_string(r, f, dconf, z->encoded, &encoded);
        if (res != OK) {
            ap_log_rerror(APLOG_MARK, APLOG_DEBUG, res, r, APLOGNO(01841)
                    "encrypt session failed");
            return res;
        }
        z->encoded = encoded;
    }

    return OK;

}

/**
 * Crypto decoding for the session.
 *
 * @param r The request pointer.
 * @param z A pointer to where the session will be written.
 */
static apr_status_t session_crypto_decode(request_rec * r,
        session_rec * z)
{

    char *encoded = NULL;
    apr_status_t res;
    const apr_crypto_t *f = NULL;
    session_crypto_dir_conf *dconf = ap_get_module_config(r->per_dir_config,
            &session_crypto_module);

    if ((dconf->passphrases_set) && z->encoded && *z->encoded) {
        apr_pool_userdata_get((void **)&f, CRYPTO_KEY,
                r->server->process->pconf);
        res = decrypt_string(r, f, dconf, z->encoded, &encoded);
        if (res != APR_SUCCESS) {
            ap_log_rerror(APLOG_MARK, APLOG_ERR, res, r, APLOGNO(01842)
                    "decrypt session failed, wrong passphrase?");
            return res;
        }
        z->encoded = encoded;
    }

    return OK;

}

/**
 * Initialise the SSL in the post_config hook.
 */
static int session_crypto_init(apr_pool_t *p, apr_pool_t *plog,
        apr_pool_t *ptemp, server_rec *s)
{
    const apr_crypto_driver_t *driver = NULL;
    apr_crypto_t *f = NULL;

    session_crypto_conf *conf = ap_get_module_config(s->module_config,
            &session_crypto_module);

    /* session_crypto_init() will be called twice. Don't bother
     * going through all of the initialization on the first call
     * because it will just be thrown away.*/
    if (ap_state_query(AP_SQ_MAIN_STATE) == AP_SQ_MS_CREATE_PRE_CONFIG) {
        return OK;
    }

    if (conf->library) {

        const apu_err_t *err = NULL;
        apr_status_t rv;

        rv = apr_crypto_init(p);
        if (APR_SUCCESS != rv) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, APLOGNO(01843)
                    "APR crypto could not be initialised");
            return rv;
        }

        rv = apr_crypto_get_driver(&driver, conf->library, conf->params, &err, p);
        if (APR_EREINIT == rv) {
            ap_log_error(APLOG_MARK, APLOG_WARNING, rv, s, APLOGNO(01844)
                    "warning: crypto for '%s' was already initialised, "
                    "using existing configuration", conf->library);
            rv = APR_SUCCESS;
        }
        if (APR_SUCCESS != rv && err) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, APLOGNO(01845)
                    "The crypto library '%s' could not be loaded: %s (%s: %d)", conf->library, err->msg, err->reason, err->rc);
            return rv;
        }
        if (APR_ENOTIMPL == rv) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, APLOGNO(01846)
                    "The crypto library '%s' could not be found",
                    conf->library);
            return rv;
        }
        if (APR_SUCCESS != rv || !driver) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, APLOGNO(01847)
                    "The crypto library '%s' could not be loaded",
                    conf->library);
            return rv;
        }

        rv = apr_crypto_make(&f, driver, conf->params, p);
        if (APR_SUCCESS != rv) {
            ap_log_error(APLOG_MARK, APLOG_ERR, rv, s, APLOGNO(01848)
                    "The crypto library '%s' could not be initialised",
                    conf->library);
            return rv;
        }

        ap_log_error(APLOG_MARK, APLOG_INFO, rv, s, APLOGNO(01849)
                "The crypto library '%s' was loaded successfully",
                conf->library);

        apr_pool_userdata_set((const void *)f, CRYPTO_KEY,
                apr_pool_cleanup_null, s->process->pconf);

    }

    return OK;
}

static void *create_session_crypto_config(apr_pool_t * p, server_rec *s)
{
    session_crypto_conf *new =
    (session_crypto_conf *) apr_pcalloc(p, sizeof(session_crypto_conf));

    /* if no library has been configured, set the recommended library
     * as a sensible default.
     */
#ifdef APU_CRYPTO_RECOMMENDED_DRIVER
    new->library = APU_CRYPTO_RECOMMENDED_DRIVER;
#endif

    return (void *) new;
}

static void *create_session_crypto_dir_config(apr_pool_t * p, char *dummy)
{
    session_crypto_dir_conf *new =
    (session_crypto_dir_conf *) apr_pcalloc(p, sizeof(session_crypto_dir_conf));

    new->passphrases = apr_array_make(p, 10, sizeof(char *));

    /* default cipher AES256-SHA */
    new->cipher = "aes256";

    return (void *) new;
}

static void *merge_session_crypto_dir_config(apr_pool_t * p, void *basev, void *addv)
{
    session_crypto_dir_conf *new = (session_crypto_dir_conf *) apr_pcalloc(p, sizeof(session_crypto_dir_conf));
    session_crypto_dir_conf *add = (session_crypto_dir_conf *) addv;
    session_crypto_dir_conf *base = (session_crypto_dir_conf *) basev;

    new->passphrases = (add->passphrases_set == 0) ? base->passphrases : add->passphrases;
    new->passphrases_set = add->passphrases_set || base->passphrases_set;
    new->cipher = (add->cipher_set == 0) ? base->cipher : add->cipher;
    new->cipher_set = add->cipher_set || base->cipher_set;

    return new;
}

static const char *set_crypto_driver(cmd_parms * cmd, void *config, const char *arg)
{
    session_crypto_conf *conf =
    (session_crypto_conf *)ap_get_module_config(cmd->server->module_config,
            &session_crypto_module);

    const char *err = ap_check_cmd_context(cmd, GLOBAL_ONLY);

    if (err != NULL) {
        return err;
    }

    conf->library = ap_getword_conf(cmd->pool, &arg);
    conf->params = arg;
    conf->library_set = 1;

    return NULL;
}

static const char *set_crypto_passphrase(cmd_parms * cmd, void *config, const char *arg)
{
    const char **passphrase;
    session_crypto_dir_conf *dconf = (session_crypto_dir_conf *) config;

    passphrase = apr_array_push(dconf->passphrases);
    *passphrase = arg;
    dconf->passphrases_set = 1;

    return NULL;
}

static const char *set_crypto_passphrase_file(cmd_parms *cmd, void *config,
                                  const char *filename)
{
    char buffer[MAX_STRING_LEN];
    char *arg;
    const char *args;
    ap_configfile_t *file;
    apr_status_t rv;

    filename = ap_server_root_relative(cmd->temp_pool, filename);
    rv = ap_pcfg_openfile(&file, cmd->temp_pool, filename);
    if (rv != APR_SUCCESS) {
        return apr_psprintf(cmd->pool, "%s: Could not open file %s: %pm",
                            cmd->cmd->name, filename, &rv);
    }

    while (!(ap_cfg_getline(buffer, sizeof(buffer), file))) {
        args = buffer;
        while (*(arg = ap_getword_conf(cmd->pool, &args)) != '\0') {
            if (*arg == '#' || *arg == 0) {
                break;
            }
            set_crypto_passphrase(cmd, config, arg);
        }
    }

    ap_cfg_closefile(file);

    return NULL;
}

static const char *set_crypto_cipher(cmd_parms * cmd, void *config, const char *cipher)
{
    session_crypto_dir_conf *dconf = (session_crypto_dir_conf *) config;

    dconf->cipher = cipher;
    dconf->cipher_set = 1;

    return NULL;
}

static const command_rec session_crypto_cmds[] =
{
    AP_INIT_ITERATE("SessionCryptoPassphrase", set_crypto_passphrase, NULL, RSRC_CONF|OR_AUTHCFG,
            "The passphrase(s) used to encrypt the session. First will be used for encryption, all phrases will be accepted for decryption"),
    AP_INIT_TAKE1("SessionCryptoPassphraseFile", set_crypto_passphrase_file, NULL, RSRC_CONF|ACCESS_CONF,
            "File containing passphrase(s) used to encrypt the session, one per line. First will be used for encryption, all phrases will be accepted for decryption"),
    AP_INIT_TAKE1("SessionCryptoCipher", set_crypto_cipher, NULL, RSRC_CONF|OR_AUTHCFG,
            "The underlying crypto cipher to use"),
    AP_INIT_RAW_ARGS("SessionCryptoDriver", set_crypto_driver, NULL, RSRC_CONF,
            "The underlying crypto library driver to use"),
    { NULL }
};

static void register_hooks(apr_pool_t * p)
{
    ap_hook_session_encode(session_crypto_encode, NULL, NULL, APR_HOOK_LAST);
    ap_hook_session_decode(session_crypto_decode, NULL, NULL, APR_HOOK_FIRST);
    ap_hook_post_config(session_crypto_init, NULL, NULL, APR_HOOK_LAST);
}

AP_DECLARE_MODULE(session_crypto) =
{
    STANDARD20_MODULE_STUFF,
    create_session_crypto_dir_config, /* dir config creater */
    merge_session_crypto_dir_config, /* dir merger --- default is to override */
    create_session_crypto_config, /* server config */
    NULL, /* merge server config */
    session_crypto_cmds, /* command apr_table_t */
    register_hooks /* register hooks */
};

#endif