openssl/crypto/ocsp/ocsp_vfy.c

/*
 * Copyright 2001-2021 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (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 <string.h>
#include <openssl/ocsp.h>
#include <openssl/err.h>
#include "internal/sizes.h"
#include "ocsp_local.h"

static int ocsp_find_signer(X509 **psigner, OCSP_BASICRESP *bs,
                            STACK_OF(X509) *certs, unsigned long flags);
static X509 *ocsp_find_signer_sk(STACK_OF(X509) *certs, OCSP_RESPID *id);
static int ocsp_check_issuer(OCSP_BASICRESP *bs, STACK_OF(X509) *chain);
static int ocsp_check_ids(STACK_OF(OCSP_SINGLERESP) *sresp,
                          OCSP_CERTID **ret);
static int ocsp_match_issuerid(X509 *cert, OCSP_CERTID *cid,
                               STACK_OF(OCSP_SINGLERESP) *sresp);
static int ocsp_check_delegated(X509 *x);
static int ocsp_req_find_signer(X509 **psigner, OCSP_REQUEST *req,
                                const X509_NAME *nm, STACK_OF(X509) *certs,
                                unsigned long flags);

/* Returns 1 on success, 0 on failure, or -1 on fatal error */
static int ocsp_verify_signer(X509 *signer, int response,
                              X509_STORE *st, unsigned long flags,
                              STACK_OF(X509) *untrusted, STACK_OF(X509) **chain)
{
    X509_STORE_CTX *ctx = X509_STORE_CTX_new();
    X509_VERIFY_PARAM *vp;
    int ret = -1;

    if (ctx == NULL) {
        ERR_raise(ERR_LIB_OCSP, ERR_R_MALLOC_FAILURE);
        goto end;
    }
    if (!X509_STORE_CTX_init(ctx, st, signer, untrusted)) {
        ERR_raise(ERR_LIB_OCSP, ERR_R_X509_LIB);
        goto end;
    }
    if ((vp = X509_STORE_CTX_get0_param(ctx)) == NULL)
        goto end;
    if ((flags & OCSP_PARTIAL_CHAIN) != 0)
        X509_VERIFY_PARAM_set_flags(vp, X509_V_FLAG_PARTIAL_CHAIN);
    if (response
            && X509_get_ext_by_NID(signer, NID_id_pkix_OCSP_noCheck, -1) >= 0)
        /*
         * Locally disable revocation status checking for OCSP responder cert.
         * Done here for CRLs; TODO should be done also for OCSP-based checks.
         */
        X509_VERIFY_PARAM_clear_flags(vp, X509_V_FLAG_CRL_CHECK);
    X509_STORE_CTX_set_purpose(ctx, X509_PURPOSE_OCSP_HELPER);
    X509_STORE_CTX_set_trust(ctx, X509_TRUST_OCSP_REQUEST);
    /* TODO: why is X509_TRUST_OCSP_REQUEST set? Seems to get ignored. */

    ret = X509_verify_cert(ctx);
    if (ret <= 0) {
        ret = X509_STORE_CTX_get_error(ctx);
        ERR_raise_data(ERR_LIB_OCSP, OCSP_R_CERTIFICATE_VERIFY_ERROR,
                       "Verify error: %s", X509_verify_cert_error_string(ret));
        goto end;
    }
    if (chain != NULL)
        *chain = X509_STORE_CTX_get1_chain(ctx);

 end:
    X509_STORE_CTX_free(ctx);
    return ret;
}

static int ocsp_verify(OCSP_REQUEST *req, OCSP_BASICRESP *bs,
                       X509 *signer, unsigned long flags)
{
    EVP_PKEY *skey;
    int ret = 1;

    if ((flags & OCSP_NOSIGS) == 0) {
        if ((skey = X509_get0_pubkey(signer)) == NULL) {
            ERR_raise(ERR_LIB_OCSP, OCSP_R_NO_SIGNER_KEY);
            return -1;
        }
        if (req != NULL)
            ret = OCSP_REQUEST_verify(req, skey, signer->libctx, signer->propq);
        else
            ret = OCSP_BASICRESP_verify(bs, skey, signer->libctx, signer->propq);
        if (ret <= 0)
            ERR_raise(ERR_LIB_OCSP, OCSP_R_SIGNATURE_FAILURE);
    }
    return ret;
}

/* Verify a basic response message */
int OCSP_basic_verify(OCSP_BASICRESP *bs, STACK_OF(X509) *certs,
                      X509_STORE *st, unsigned long flags)
{
    X509 *signer, *x;
    STACK_OF(X509) *chain = NULL;
    STACK_OF(X509) *untrusted = NULL;
    int ret = ocsp_find_signer(&signer, bs, certs, flags);

    if (ret == 0) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_SIGNER_CERTIFICATE_NOT_FOUND);
        goto end;
    }
    if ((ret == 2) && (flags & OCSP_TRUSTOTHER) != 0)
        flags |= OCSP_NOVERIFY;

    if ((ret = ocsp_verify(NULL, bs, signer, flags)) <= 0)
        goto end;
    if ((flags & OCSP_NOVERIFY) == 0) {
        ret = -1;
        if ((flags & OCSP_NOCHAIN) == 0) {
            if ((untrusted = sk_X509_dup(bs->certs)) == NULL)
                goto end;
            if (!X509_add_certs(untrusted, certs, X509_ADD_FLAG_DEFAULT))
                goto end;
        }
        ret = ocsp_verify_signer(signer, 1, st, flags, untrusted, &chain);
        if (ret <= 0)
            goto end;
        if ((flags & OCSP_NOCHECKS) != 0) {
            ret = 1;
            goto end;
        }
        /*
         * At this point we have a valid certificate chain need to verify it
         * against the OCSP issuer criteria.
         */
        ret = ocsp_check_issuer(bs, chain);

        /* If fatal error or valid match then finish */
        if (ret != 0)
            goto end;

        /*
         * Easy case: explicitly trusted. Get root CA and check for explicit
         * trust
         */
        if ((flags & OCSP_NOEXPLICIT) != 0)
            goto end;

        x = sk_X509_value(chain, sk_X509_num(chain) - 1);
        if (X509_check_trust(x, NID_OCSP_sign, 0) != X509_TRUST_TRUSTED) {
            ERR_raise(ERR_LIB_OCSP, OCSP_R_ROOT_CA_NOT_TRUSTED);
            ret = 0;
            goto end;
        }
        ret = 1;
    }

 end:
    sk_X509_pop_free(chain, X509_free);
    sk_X509_free(untrusted);
    return ret;
}

int OCSP_resp_get0_signer(OCSP_BASICRESP *bs, X509 **signer,
                          STACK_OF(X509) *extra_certs)
{
    return ocsp_find_signer(signer, bs, extra_certs, 0) > 0;
}

static int ocsp_find_signer(X509 **psigner, OCSP_BASICRESP *bs,
                            STACK_OF(X509) *certs, unsigned long flags)
{
    X509 *signer;
    OCSP_RESPID *rid = &bs->tbsResponseData.responderId;

    if ((signer = ocsp_find_signer_sk(certs, rid)) != NULL) {
        *psigner = signer;
        return 2;
    }
    if ((flags & OCSP_NOINTERN) == 0 &&
        (signer = ocsp_find_signer_sk(bs->certs, rid))) {
        *psigner = signer;
        return 1;
    }
    /* Maybe lookup from store if by subject name */

    *psigner = NULL;
    return 0;
}

static X509 *ocsp_find_signer_sk(STACK_OF(X509) *certs, OCSP_RESPID *id)
{
    int i, r;
    unsigned char tmphash[SHA_DIGEST_LENGTH], *keyhash;
    EVP_MD *md;
    X509 *x;

    /* Easy if lookup by name */
    if (id->type == V_OCSP_RESPID_NAME)
        return X509_find_by_subject(certs, id->value.byName);

    /* Lookup by key hash */

    /* If key hash isn't SHA1 length then forget it */
    if (id->value.byKey->length != SHA_DIGEST_LENGTH)
        return NULL;
    keyhash = id->value.byKey->data;
    /* Calculate hash of each key and compare */
    for (i = 0; i < sk_X509_num(certs); i++) {
        if ((x = sk_X509_value(certs, i)) != NULL) {
            if ((md = EVP_MD_fetch(x->libctx, SN_sha1, x->propq)) == NULL)
                break;
            r = X509_pubkey_digest(x, md, tmphash, NULL);
            EVP_MD_free(md);
            if (!r)
                break;
            if (memcmp(keyhash, tmphash, SHA_DIGEST_LENGTH) == 0)
                return x;
        }
    }
    return NULL;
}

static int ocsp_check_issuer(OCSP_BASICRESP *bs, STACK_OF(X509) *chain)
{
    STACK_OF(OCSP_SINGLERESP) *sresp = bs->tbsResponseData.responses;
    X509 *signer, *sca;
    OCSP_CERTID *caid = NULL;
    int ret;

    if (sk_X509_num(chain) <= 0) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_NO_CERTIFICATES_IN_CHAIN);
        return -1;
    }

    /* See if the issuer IDs match. */
    ret = ocsp_check_ids(sresp, &caid);

    /* If ID mismatch or other error then return */
    if (ret <= 0)
        return ret;

    signer = sk_X509_value(chain, 0);
    /* Check to see if OCSP responder CA matches request CA */
    if (sk_X509_num(chain) > 1) {
        sca = sk_X509_value(chain, 1);
        ret = ocsp_match_issuerid(sca, caid, sresp);
        if (ret < 0)
            return ret;
        if (ret != 0) {
            /* We have a match, if extensions OK then success */
            if (ocsp_check_delegated(signer))
                return 1;
            return 0;
        }
    }

    /* Otherwise check if OCSP request signed directly by request CA */
    return ocsp_match_issuerid(signer, caid, sresp);
}

/*
 * Check the issuer certificate IDs for equality. If there is a mismatch with
 * the same algorithm then there's no point trying to match any certificates
 * against the issuer. If the issuer IDs all match then we just need to check
 * equality against one of them.
 */

static int ocsp_check_ids(STACK_OF(OCSP_SINGLERESP) *sresp, OCSP_CERTID **ret)
{
    OCSP_CERTID *tmpid, *cid;
    int i, idcount;

    idcount = sk_OCSP_SINGLERESP_num(sresp);
    if (idcount <= 0) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_RESPONSE_CONTAINS_NO_REVOCATION_DATA);
        return -1;
    }

    cid = sk_OCSP_SINGLERESP_value(sresp, 0)->certId;

    *ret = NULL;
    for (i = 1; i < idcount; i++) {
        tmpid = sk_OCSP_SINGLERESP_value(sresp, i)->certId;
        /* Check to see if IDs match */
        if (OCSP_id_issuer_cmp(cid, tmpid)) {
            /* If algorithm mismatch let caller deal with it */
            if (OBJ_cmp(tmpid->hashAlgorithm.algorithm,
                        cid->hashAlgorithm.algorithm))
                return 2;
            /* Else mismatch */
            return 0;
        }
    }

    /* All IDs match: only need to check one ID */
    *ret = cid;
    return 1;
}

/*
 * Match the certificate issuer ID.
 * Returns -1 on fatal error, 0 if there is no match and 1 if there is a match.
 */
static int ocsp_match_issuerid(X509 *cert, OCSP_CERTID *cid,
                               STACK_OF(OCSP_SINGLERESP) *sresp)
{
    int ret = -1;
    EVP_MD *dgst = NULL;

    /* If only one ID to match then do it */
    if (cid != NULL) {
        char name[OSSL_MAX_NAME_SIZE];
        const X509_NAME *iname;
        int mdlen;
        unsigned char md[EVP_MAX_MD_SIZE];

        OBJ_obj2txt(name, sizeof(name), cid->hashAlgorithm.algorithm, 0);

        (void)ERR_set_mark();
        dgst = EVP_MD_fetch(NULL, name, NULL);
        if (dgst == NULL)
            dgst = (EVP_MD *)EVP_get_digestbyname(name);

        if (dgst == NULL) {
            (void)ERR_clear_last_mark();
            ERR_raise(ERR_LIB_OCSP, OCSP_R_UNKNOWN_MESSAGE_DIGEST);
            goto end;
        }
        (void)ERR_pop_to_mark();

        mdlen = EVP_MD_size(dgst);
        if (mdlen < 0) {
            ERR_raise(ERR_LIB_OCSP, OCSP_R_DIGEST_SIZE_ERR);
            goto end;
        }
        if (cid->issuerNameHash.length != mdlen ||
            cid->issuerKeyHash.length != mdlen) {
            ret = 0;
            goto end;
        }
        iname = X509_get_subject_name(cert);
        if (!X509_NAME_digest(iname, dgst, md, NULL))
            goto end;
        if (memcmp(md, cid->issuerNameHash.data, mdlen) != 0) {
            ret = 0;
            goto end;
        }
        if (!X509_pubkey_digest(cert, dgst, md, NULL)) {
            ERR_raise(ERR_LIB_OCSP, OCSP_R_DIGEST_ERR);
            goto end;
        }
        ret = memcmp(md, cid->issuerKeyHash.data, mdlen) == 0;
        goto end;
    } else {
        /* We have to match the whole lot */
        int i;
        OCSP_CERTID *tmpid;

        for (i = 0; i < sk_OCSP_SINGLERESP_num(sresp); i++) {
            tmpid = sk_OCSP_SINGLERESP_value(sresp, i)->certId;
            ret = ocsp_match_issuerid(cert, tmpid, NULL);
            if (ret <= 0)
                return ret;
        }
    }
    return 1;
end:
    EVP_MD_free(dgst);
    return ret;
}

static int ocsp_check_delegated(X509 *x)
{
    if ((X509_get_extension_flags(x) & EXFLAG_XKUSAGE)
        && (X509_get_extended_key_usage(x) & XKU_OCSP_SIGN))
        return 1;
    ERR_raise(ERR_LIB_OCSP, OCSP_R_MISSING_OCSPSIGNING_USAGE);
    return 0;
}

/*
 * Verify an OCSP request. This is much easier than OCSP response verify.
 * Just find the signer's certificate and verify it against a given trust value.
 * Returns 1 on success, 0 on failure and on fatal error.
 */
int OCSP_request_verify(OCSP_REQUEST *req, STACK_OF(X509) *certs,
                        X509_STORE *store, unsigned long flags)
{
    X509 *signer;
    const X509_NAME *nm;
    GENERAL_NAME *gen;
    int ret;

    if (!req->optionalSignature) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_REQUEST_NOT_SIGNED);
        return 0;
    }
    gen = req->tbsRequest.requestorName;
    if (!gen || gen->type != GEN_DIRNAME) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_UNSUPPORTED_REQUESTORNAME_TYPE);
        return 0; /* not returning -1 here for backward compatibility*/
    }
    nm = gen->d.directoryName;
    ret = ocsp_req_find_signer(&signer, req, nm, certs, flags);
    if (ret <= 0) {
        ERR_raise(ERR_LIB_OCSP, OCSP_R_SIGNER_CERTIFICATE_NOT_FOUND);
        return 0; /* not returning -1 here for backward compatibility*/
    }
    if ((ret == 2) && (flags & OCSP_TRUSTOTHER) != 0)
        flags |= OCSP_NOVERIFY;

    if ((ret = ocsp_verify(req, NULL, signer, flags)) <= 0)
        return 0; /* not returning 'ret' here for backward compatibility*/
    if ((flags & OCSP_NOVERIFY) != 0)
        return 1;
    return ocsp_verify_signer(signer, 0, store, flags,
                              (flags & OCSP_NOCHAIN) != 0 ?
                              NULL : req->optionalSignature->certs, NULL) > 0;
    /* using '> 0' here to avoid breaking backward compatibility returning -1 */
}

static int ocsp_req_find_signer(X509 **psigner, OCSP_REQUEST *req,
                                const X509_NAME *nm, STACK_OF(X509) *certs,
                                unsigned long flags)
{
    X509 *signer;

    if ((flags & OCSP_NOINTERN) == 0) {
        signer = X509_find_by_subject(req->optionalSignature->certs, nm);
        if (signer != NULL) {
            *psigner = signer;
            return 1;
        }
    }

    if ((signer = X509_find_by_subject(certs, nm)) != NULL) {
        *psigner = signer;
        return 2;
    }
    return 0;
}