eng_dyn.c

/*
 * Copyright 2001-2022 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include "eng_local.h"
#include "internal/dso.h"
#include <openssl/crypto.h>

/*
 * Shared libraries implementing ENGINEs for use by the "dynamic" ENGINE
 * loader should implement the hook-up functions with the following
 * prototypes.
 */

/* Our ENGINE handlers */
static int dynamic_init(ENGINE *e);
static int dynamic_finish(ENGINE *e);
static int dynamic_ctrl(ENGINE *e, int cmd, long i, void *p,
                        void (*f) (void));
/* Predeclare our context type */
typedef struct st_dynamic_data_ctx dynamic_data_ctx;
/* The implementation for the important control command */
static int dynamic_load(ENGINE *e, dynamic_data_ctx *ctx);

#define DYNAMIC_CMD_SO_PATH             ENGINE_CMD_BASE
#define DYNAMIC_CMD_NO_VCHECK           (ENGINE_CMD_BASE + 1)
#define DYNAMIC_CMD_ID                  (ENGINE_CMD_BASE + 2)
#define DYNAMIC_CMD_LIST_ADD            (ENGINE_CMD_BASE + 3)
#define DYNAMIC_CMD_DIR_LOAD            (ENGINE_CMD_BASE + 4)
#define DYNAMIC_CMD_DIR_ADD             (ENGINE_CMD_BASE + 5)
#define DYNAMIC_CMD_LOAD                (ENGINE_CMD_BASE + 6)

/* The constants used when creating the ENGINE */
static const char *engine_dynamic_id = "dynamic";
static const char *engine_dynamic_name = "Dynamic engine loading support";
static const ENGINE_CMD_DEFN dynamic_cmd_defns[] = {
    {DYNAMIC_CMD_SO_PATH,
     "SO_PATH",
     "Specifies the path to the new ENGINE shared library",
     ENGINE_CMD_FLAG_STRING},
    {DYNAMIC_CMD_NO_VCHECK,
     "NO_VCHECK",
     "Specifies to continue even if version checking fails (boolean)",
     ENGINE_CMD_FLAG_NUMERIC},
    {DYNAMIC_CMD_ID,
     "ID",
     "Specifies an ENGINE id name for loading",
     ENGINE_CMD_FLAG_STRING},
    {DYNAMIC_CMD_LIST_ADD,
     "LIST_ADD",
     "Whether to add a loaded ENGINE to the internal list (0=no,1=yes,2=mandatory)",
     ENGINE_CMD_FLAG_NUMERIC},
    {DYNAMIC_CMD_DIR_LOAD,
     "DIR_LOAD",
     "Specifies whether to load from 'DIR_ADD' directories (0=no,1=yes,2=mandatory)",
     ENGINE_CMD_FLAG_NUMERIC},
    {DYNAMIC_CMD_DIR_ADD,
     "DIR_ADD",
     "Adds a directory from which ENGINEs can be loaded",
     ENGINE_CMD_FLAG_STRING},
    {DYNAMIC_CMD_LOAD,
     "LOAD",
     "Load up the ENGINE specified by other settings",
     ENGINE_CMD_FLAG_NO_INPUT},
    {0, NULL, NULL, 0}
};

/*
 * Loading code stores state inside the ENGINE structure via the "ex_data"
 * element. We load all our state into a single structure and use that as a
 * single context in the "ex_data" stack.
 */
struct st_dynamic_data_ctx {
    /* The DSO object we load that supplies the ENGINE code */
    DSO *dynamic_dso;
    /*
     * The function pointer to the version checking shared library function
     */
    dynamic_v_check_fn v_check;
    /*
     * The function pointer to the engine-binding shared library function
     */
    dynamic_bind_engine bind_engine;
    /* The default name/path for loading the shared library */
    char *DYNAMIC_LIBNAME;
    /* Whether to continue loading on a version check failure */
    int no_vcheck;
    /* If non-NULL, stipulates the 'id' of the ENGINE to be loaded */
    char *engine_id;
    /*
     * If non-zero, a successfully loaded ENGINE should be added to the
     * internal ENGINE list. If 2, the add must succeed or the entire load
     * should fail.
     */
    int list_add_value;
    /* The symbol name for the version checking function */
    const char *DYNAMIC_F1;
    /* The symbol name for the "initialise ENGINE structure" function */
    const char *DYNAMIC_F2;
    /*
     * Whether to never use 'dirs', use 'dirs' as a fallback, or only use
     * 'dirs' for loading. Default is to use 'dirs' as a fallback.
     */
    int dir_load;
    /* A stack of directories from which ENGINEs could be loaded */
    STACK_OF(OPENSSL_STRING) *dirs;
};

/*
 * This is the "ex_data" index we obtain and reserve for use with our context
 * structure.
 */
static int dynamic_ex_data_idx = -1;

static void int_free_str(char *s)
{
    OPENSSL_free(s);
}

/*
 * Because our ex_data element may or may not get allocated depending on
 * whether a "first-use" occurs before the ENGINE is freed, we have a memory
 * leak problem to solve. We can't declare a "new" handler for the ex_data as
 * we don't want a dynamic_data_ctx in *all* ENGINE structures of all types
 * (this is a bug in the design of CRYPTO_EX_DATA). As such, we just declare
 * a "free" handler and that will get called if an ENGINE is being destroyed
 * and there was an ex_data element corresponding to our context type.
 */
static void dynamic_data_ctx_free_func(void *parent, void *ptr,
                                       CRYPTO_EX_DATA *ad, int idx, long argl,
                                       void *argp)
{
    if (ptr) {
        dynamic_data_ctx *ctx = (dynamic_data_ctx *)ptr;
        DSO_free(ctx->dynamic_dso);
        OPENSSL_free(ctx->DYNAMIC_LIBNAME);
        OPENSSL_free(ctx->engine_id);
        sk_OPENSSL_STRING_pop_free(ctx->dirs, int_free_str);
        OPENSSL_free(ctx);
    }
}

/*
 * Construct the per-ENGINE context. We create it blindly and then use a lock
 * to check for a race - if so, all but one of the threads "racing" will have
 * wasted their time. The alternative involves creating everything inside the
 * lock which is far worse.
 */
static int dynamic_set_data_ctx(ENGINE *e, dynamic_data_ctx **ctx)
{
    dynamic_data_ctx *c = OPENSSL_zalloc(sizeof(*c));
    int ret = 1;

    if (c == NULL) {
        ENGINEerr(ENGINE_F_DYNAMIC_SET_DATA_CTX, ERR_R_MALLOC_FAILURE);
        return 0;
    }
    c->dirs = sk_OPENSSL_STRING_new_null();
    if (c->dirs == NULL) {
        ENGINEerr(ENGINE_F_DYNAMIC_SET_DATA_CTX, ERR_R_MALLOC_FAILURE);
        OPENSSL_free(c);
        return 0;
    }
    c->DYNAMIC_F1 = "v_check";
    c->DYNAMIC_F2 = "bind_engine";
    c->dir_load = 1;
    CRYPTO_THREAD_write_lock(global_engine_lock);
    if ((*ctx = (dynamic_data_ctx *)ENGINE_get_ex_data(e,
                                                       dynamic_ex_data_idx))
        == NULL) {
        /* Good, we're the first */
        ret = ENGINE_set_ex_data(e, dynamic_ex_data_idx, c);
        if (ret) {
            *ctx = c;
            c = NULL;
        }
    }
    CRYPTO_THREAD_unlock(global_engine_lock);
    /*
     * If we lost the race to set the context, c is non-NULL and *ctx is the
     * context of the thread that won.
     */
    if (c)
        sk_OPENSSL_STRING_free(c->dirs);
    OPENSSL_free(c);
    return ret;
}

/*
 * This function retrieves the context structure from an ENGINE's "ex_data",
 * or if it doesn't exist yet, sets it up.
 */
static dynamic_data_ctx *dynamic_get_data_ctx(ENGINE *e)
{
    dynamic_data_ctx *ctx;
    if (dynamic_ex_data_idx < 0) {
        /*
         * Create and register the ENGINE ex_data, and associate our "free"
         * function with it to ensure any allocated contexts get freed when
         * an ENGINE goes underground.
         */
        int new_idx = ENGINE_get_ex_new_index(0, NULL, NULL, NULL,
                                              dynamic_data_ctx_free_func);
        if (new_idx == -1) {
            ENGINEerr(ENGINE_F_DYNAMIC_GET_DATA_CTX, ENGINE_R_NO_INDEX);
            return NULL;
        }
        CRYPTO_THREAD_write_lock(global_engine_lock);
        /* Avoid a race by checking again inside this lock */
        if (dynamic_ex_data_idx < 0) {
            /* Good, someone didn't beat us to it */
            dynamic_ex_data_idx = new_idx;
            new_idx = -1;
        }
        CRYPTO_THREAD_unlock(global_engine_lock);
        /*
         * In theory we could "give back" the index here if (new_idx>-1), but
         * it's not possible and wouldn't gain us much if it were.
         */
    }
    ctx = (dynamic_data_ctx *)ENGINE_get_ex_data(e, dynamic_ex_data_idx);
    /* Check if the context needs to be created */
    if ((ctx == NULL) && !dynamic_set_data_ctx(e, &ctx))
        /* "set_data" will set errors if necessary */
        return NULL;
    return ctx;
}

static ENGINE *engine_dynamic(void)
{
    ENGINE *ret = ENGINE_new();
    if (ret == NULL)
        return NULL;
    if (!ENGINE_set_id(ret, engine_dynamic_id) ||
        !ENGINE_set_name(ret, engine_dynamic_name) ||
        !ENGINE_set_init_function(ret, dynamic_init) ||
        !ENGINE_set_finish_function(ret, dynamic_finish) ||
        !ENGINE_set_ctrl_function(ret, dynamic_ctrl) ||
        !ENGINE_set_flags(ret, ENGINE_FLAGS_BY_ID_COPY) ||
        !ENGINE_set_cmd_defns(ret, dynamic_cmd_defns)) {
        ENGINE_free(ret);
        return NULL;
    }
    return ret;
}

void engine_load_dynamic_int(void)
{
    ENGINE *toadd = engine_dynamic();
    if (!toadd)
        return;
    ENGINE_add(toadd);
    /*
     * If the "add" worked, it gets a structural reference. So either way, we
     * release our just-created reference.
     */
    ENGINE_free(toadd);
    /*
     * If the "add" didn't work, it was probably a conflict because it was
     * already added (eg. someone calling ENGINE_load_blah then calling
     * ENGINE_load_builtin_engines() perhaps).
     */
    ERR_clear_error();
}

static int dynamic_init(ENGINE *e)
{
    /*
     * We always return failure - the "dynamic" engine itself can't be used
     * for anything.
     */
    return 0;
}

static int dynamic_finish(ENGINE *e)
{
    /*
     * This should never be called on account of "dynamic_init" always
     * failing.
     */
    return 0;
}

static int dynamic_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f) (void))
{
    dynamic_data_ctx *ctx = dynamic_get_data_ctx(e);
    int initialised;

    if (!ctx) {
        ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_NOT_LOADED);
        return 0;
    }
    initialised = ((ctx->dynamic_dso == NULL) ? 0 : 1);
    /* All our control commands require the ENGINE to be uninitialised */
    if (initialised) {
        ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_ALREADY_LOADED);
        return 0;
    }
    switch (cmd) {
    case DYNAMIC_CMD_SO_PATH:
        /* a NULL 'p' or a string of zero-length is the same thing */
        if (p && (strlen((const char *)p) < 1))
            p = NULL;
        OPENSSL_free(ctx->DYNAMIC_LIBNAME);
        if (p)
            ctx->DYNAMIC_LIBNAME = OPENSSL_strdup(p);
        else
            ctx->DYNAMIC_LIBNAME = NULL;
        return (ctx->DYNAMIC_LIBNAME ? 1 : 0);
    case DYNAMIC_CMD_NO_VCHECK:
        ctx->no_vcheck = ((i == 0) ? 0 : 1);
        return 1;
    case DYNAMIC_CMD_ID:
        /* a NULL 'p' or a string of zero-length is the same thing */
        if (p && (strlen((const char *)p) < 1))
            p = NULL;
        OPENSSL_free(ctx->engine_id);
        if (p)
            ctx->engine_id = OPENSSL_strdup(p);
        else
            ctx->engine_id = NULL;
        return (ctx->engine_id ? 1 : 0);
    case DYNAMIC_CMD_LIST_ADD:
        if ((i < 0) || (i > 2)) {
            ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_INVALID_ARGUMENT);
            return 0;
        }
        ctx->list_add_value = (int)i;
        return 1;
    case DYNAMIC_CMD_LOAD:
        return dynamic_load(e, ctx);
    case DYNAMIC_CMD_DIR_LOAD:
        if ((i < 0) || (i > 2)) {
            ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_INVALID_ARGUMENT);
            return 0;
        }
        ctx->dir_load = (int)i;
        return 1;
    case DYNAMIC_CMD_DIR_ADD:
        /* a NULL 'p' or a string of zero-length is the same thing */
        if (!p || (strlen((const char *)p) < 1)) {
            ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_INVALID_ARGUMENT);
            return 0;
        }
        {
            char *tmp_str = OPENSSL_strdup(p);
            if (tmp_str == NULL) {
                ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ERR_R_MALLOC_FAILURE);
                return 0;
            }
            if (!sk_OPENSSL_STRING_push(ctx->dirs, tmp_str)) {
                OPENSSL_free(tmp_str);
                ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ERR_R_MALLOC_FAILURE);
                return 0;
            }
        }
        return 1;
    default:
        break;
    }
    ENGINEerr(ENGINE_F_DYNAMIC_CTRL, ENGINE_R_CTRL_COMMAND_NOT_IMPLEMENTED);
    return 0;
}

static int int_load(dynamic_data_ctx *ctx)
{
    int num, loop;
    /* Unless told not to, try a direct load */
    if ((ctx->dir_load != 2) && (DSO_load(ctx->dynamic_dso,
                                          ctx->DYNAMIC_LIBNAME, NULL,
                                          0)) != NULL)
        return 1;
    /* If we're not allowed to use 'dirs' or we have none, fail */
    if (!ctx->dir_load || (num = sk_OPENSSL_STRING_num(ctx->dirs)) < 1)
        return 0;
    for (loop = 0; loop < num; loop++) {
        const char *s = sk_OPENSSL_STRING_value(ctx->dirs, loop);
        char *merge = DSO_merge(ctx->dynamic_dso, ctx->DYNAMIC_LIBNAME, s);
        if (!merge)
            return 0;
        if (DSO_load(ctx->dynamic_dso, merge, NULL, 0)) {
            /* Found what we're looking for */
            OPENSSL_free(merge);
            return 1;
        }
        OPENSSL_free(merge);
    }
    return 0;
}

static int dynamic_load(ENGINE *e, dynamic_data_ctx *ctx)
{
    ENGINE cpy;
    dynamic_fns fns;

    if (ctx->dynamic_dso == NULL)
        ctx->dynamic_dso = DSO_new();
    if (ctx->dynamic_dso == NULL)
        return 0;
    if (!ctx->DYNAMIC_LIBNAME) {
        if (!ctx->engine_id)
            return 0;
        DSO_ctrl(ctx->dynamic_dso, DSO_CTRL_SET_FLAGS,
                 DSO_FLAG_NAME_TRANSLATION_EXT_ONLY, NULL);
        ctx->DYNAMIC_LIBNAME =
            DSO_convert_filename(ctx->dynamic_dso, ctx->engine_id);
    }
    if (!int_load(ctx)) {
        ENGINEerr(ENGINE_F_DYNAMIC_LOAD, ENGINE_R_DSO_NOT_FOUND);
        DSO_free(ctx->dynamic_dso);
        ctx->dynamic_dso = NULL;
        return 0;
    }
    /* We have to find a bind function otherwise it'll always end badly */
    if (!
        (ctx->bind_engine =
         (dynamic_bind_engine) DSO_bind_func(ctx->dynamic_dso,
                                             ctx->DYNAMIC_F2))) {
        ctx->bind_engine = NULL;
        DSO_free(ctx->dynamic_dso);
        ctx->dynamic_dso = NULL;
        ENGINEerr(ENGINE_F_DYNAMIC_LOAD, ENGINE_R_DSO_FAILURE);
        return 0;
    }
    /* Do we perform version checking? */
    if (!ctx->no_vcheck) {
        unsigned long vcheck_res = 0;
        /*
         * Now we try to find a version checking function and decide how to
         * cope with failure if/when it fails.
         */
        ctx->v_check =
            (dynamic_v_check_fn) DSO_bind_func(ctx->dynamic_dso,
                                               ctx->DYNAMIC_F1);
        if (ctx->v_check)
            vcheck_res = ctx->v_check(OSSL_DYNAMIC_VERSION);
        /*
         * We fail if the version checker veto'd the load *or* if it is
         * deferring to us (by returning its version) and we think it is too
         * old.
         * Unfortunately the version checker does not distinguish between
         * engines built for openssl 1.1.x and openssl 3.x, but loading
         * an engine that is built for openssl 3.x will cause a fatal
         * error.  Detect such engines, since EVP_PKEY_get_base_id is exported
         * as a function in openssl 3.x, while it is named EVP_PKEY_base_id
         * in openssl 1.1.x.  Therefore we take the presence of that symbol
         * as an indication that the engine will be incompatible.
         */
        if (vcheck_res < OSSL_DYNAMIC_OLDEST
                || DSO_bind_func(ctx->dynamic_dso,
                                 "EVP_PKEY_get_base_id") != NULL) {
            /* Fail */
            ctx->bind_engine = NULL;
            ctx->v_check = NULL;
            DSO_free(ctx->dynamic_dso);
            ctx->dynamic_dso = NULL;
            ENGINEerr(ENGINE_F_DYNAMIC_LOAD,
                      ENGINE_R_VERSION_INCOMPATIBILITY);
            return 0;
        }
    }
    /*
     * First binary copy the ENGINE structure so that we can roll back if the
     * hand-over fails
     */
    memcpy(&cpy, e, sizeof(ENGINE));
    /*
     * Provide the ERR, "ex_data", memory, and locking callbacks so the
     * loaded library uses our state rather than its own. FIXME: As noted in
     * engine.h, much of this would be simplified if each area of code
     * provided its own "summary" structure of all related callbacks. It
     * would also increase opaqueness.
     */
    fns.static_state = ENGINE_get_static_state();
    CRYPTO_get_mem_functions(&fns.mem_fns.malloc_fn, &fns.mem_fns.realloc_fn,
                             &fns.mem_fns.free_fn);
    /*
     * Now that we've loaded the dynamic engine, make sure no "dynamic"
     * ENGINE elements will show through.
     */
    engine_set_all_null(e);

    /* Try to bind the ENGINE onto our own ENGINE structure */
    if (!engine_add_dynamic_id(e, (ENGINE_DYNAMIC_ID)ctx->bind_engine, 1)
            || !ctx->bind_engine(e, ctx->engine_id, &fns)) {
        engine_remove_dynamic_id(e, 1);
        ctx->bind_engine = NULL;
        ctx->v_check = NULL;
        DSO_free(ctx->dynamic_dso);
        ctx->dynamic_dso = NULL;
        ENGINEerr(ENGINE_F_DYNAMIC_LOAD, ENGINE_R_INIT_FAILED);
        /* Copy the original ENGINE structure back */
        memcpy(e, &cpy, sizeof(ENGINE));
        return 0;
    }
    /* Do we try to add this ENGINE to the internal list too? */
    if (ctx->list_add_value > 0) {
        if (!ENGINE_add(e)) {
            /* Do we tolerate this or fail? */
            if (ctx->list_add_value > 1) {
                /*
                 * Fail - NB: By this time, it's too late to rollback, and
                 * trying to do so allows the bind_engine() code to have
                 * created leaks. We just have to fail where we are, after
                 * the ENGINE has changed.
                 */
                ENGINEerr(ENGINE_F_DYNAMIC_LOAD,
                          ENGINE_R_CONFLICTING_ENGINE_ID);
                return 0;
            }
            /* Tolerate */
            ERR_clear_error();
        }
    }
    return 1;
}