Commit message: Check that multi-strings/CHOICE types don't use implicit tagging

It never makes sense for multi-string or CHOICE types to use implicit
tagging since the content would be ambiguous. It is an error in the
template if this ever happens. If we detect it we should stop parsing.

Thanks to David Benjamin from Google for reporting this issue.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
CVE: CVE-2020-1971
CWE: CWE-476
Vulnerability description: The X.509 GeneralName type is a generic type for representing different types of names. One of those name types is known as EDIPartyName. OpenSSL provides a function GENERAL_NAME_cmp which compares different instances of a GENERAL_NAME to see if they are equal or not. This function behaves incorrectly when both GENERAL_NAMEs contain an EDIPARTYNAME. A NULL pointer dereference and a crash may occur leading to a possible denial of service attack. OpenSSL itself uses the GENERAL_NAME_cmp function for two purposes: 1) Comparing CRL distribution point names between an available CRL and a CRL distribution point embedded in an X509 certificate 2) When verifying that a timestamp response token signer matches the timestamp authority name (exposed via the API functions TS_RESP_verify_response and TS_RESP_verify_token) If an attacker can control both items being compared then that attacker could trigger a crash. For example if the attacker can trick a client or server into checking a malicious certificate against a malicious CRL then this may occur. Note that some applications automatically download CRLs based on a URL embedded in a certificate. This checking happens prior to the signatures on the certificate and CRL being verified. OpenSSL's s_server, s_client and verify tools have support for the "-crl_download" option which implements automatic CRL downloading and this attack has been demonstrated to work against those tools. Note that an unrelated bug means that affected versions of OpenSSL cannot parse or construct correct encodings of EDIPARTYNAME. However it is possible to construct a malformed EDIPARTYNAME that OpenSSL's parser will accept and hence trigger this attack. All OpenSSL 1.1.1 and 1.0.2 versions are affected by this issue. Other OpenSSL releases are out of support and have not been checked. Fixed in OpenSSL 1.1.1i (Affected 1.1.1-1.1.1h). Fixed in OpenSSL 1.0.2x (Affected 1.0.2-1.0.2w).

Project: openssl

static int asn1_item_embed_d2i(ASN1_VALUE **pval, const unsigned char **in,
                               long len, const ASN1_ITEM *it,
                               int tag, int aclass, char opt, ASN1_TLC *ctx,
                               int depth)
{
    const ASN1_TEMPLATE *tt, *errtt = NULL;
    const ASN1_EXTERN_FUNCS *ef;
    const ASN1_AUX *aux = it->funcs;
    ASN1_aux_cb *asn1_cb;
    const unsigned char *p = NULL, *q;
    unsigned char oclass;
    char seq_eoc, seq_nolen, cst, isopt;
    long tmplen;
    int i;
    int otag;
    int ret = 0;
    ASN1_VALUE **pchptr;

    if (pval == NULL)
        return 0;
    if (aux && aux->asn1_cb)
        asn1_cb = aux->asn1_cb;
    else
        asn1_cb = 0;

    if (++depth > ASN1_MAX_CONSTRUCTED_NEST) {
        ERR_raise(ERR_LIB_ASN1, ASN1_R_NESTED_TOO_DEEP);
        goto err;
    }

    switch (it->itype) {
    case ASN1_ITYPE_PRIMITIVE:
        if (it->templates) {
            /*
             * tagging or OPTIONAL is currently illegal on an item template
             * because the flags can't get passed down. In practice this
             * isn't a problem: we include the relevant flags from the item
             * template in the template itself.
             */
            if ((tag != -1) || opt) {
                ERR_raise(ERR_LIB_ASN1,
                          ASN1_R_ILLEGAL_OPTIONS_ON_ITEM_TEMPLATE);
                goto err;
            }
            return asn1_template_ex_d2i(pval, in, len,
                                        it->templates, opt, ctx, depth);
        }
        return asn1_d2i_ex_primitive(pval, in, len, it,
                                     tag, aclass, opt, ctx);

    case ASN1_ITYPE_MSTRING:
        p = *in;
        /* Just read in tag and class */
        ret = asn1_check_tlen(NULL, &otag, &oclass, NULL, NULL,
                              &p, len, -1, 0, 1, ctx);
        if (!ret) {
            ERR_raise(ERR_LIB_ASN1, ERR_R_NESTED_ASN1_ERROR);
            goto err;
        }

        /* Must be UNIVERSAL class */
        if (oclass != V_ASN1_UNIVERSAL) {
            /* If OPTIONAL, assume this is OK */
            if (opt)
                return -1;
            ERR_raise(ERR_LIB_ASN1, ASN1_R_MSTRING_NOT_UNIVERSAL);
            goto err;
        }
        /* Check tag matches bit map */
        if (!(ASN1_tag2bit(otag) & it->utype)) {
            /* If OPTIONAL, assume this is OK */
            if (opt)
                return -1;
            ERR_raise(ERR_LIB_ASN1, ASN1_R_MSTRING_WRONG_TAG);
            goto err;
        }
        return asn1_d2i_ex_primitive(pval, in, len, it, otag, 0, 0, ctx);

    case ASN1_ITYPE_EXTERN:
        /* Use new style d2i */
        ef = it->funcs;
        return ef->asn1_ex_d2i(pval, in, len, it, tag, aclass, opt, ctx);

    case ASN1_ITYPE_CHOICE:
        if (asn1_cb && !asn1_cb(ASN1_OP_D2I_PRE, pval, it, NULL))
            goto auxerr;
        if (*pval) {
            /* Free up and zero CHOICE value if initialised */
            i = asn1_get_choice_selector(pval, it);
            if ((i >= 0) && (i < it->tcount)) {
                tt = it->templates + i;
                pchptr = asn1_get_field_ptr(pval, tt);
                asn1_template_free(pchptr, tt);
                asn1_set_choice_selector(pval, -1, it);
            }
        } else if (!ASN1_item_ex_new(pval, it)) {
            ERR_raise(ERR_LIB_ASN1, ERR_R_NESTED_ASN1_ERROR);
            goto err;
        }
        /* CHOICE type, try each possibility in turn */
        p = *in;
        for (i = 0, tt = it->templates; i < it->tcount; i++, tt++) {
            pchptr = asn1_get_field_ptr(pval, tt);
            /*
             * We mark field as OPTIONAL so its absence can be recognised.
             */
            ret = asn1_template_ex_d2i(pchptr, &p, len, tt, 1, ctx, depth);
            /* If field not present, try the next one */
            if (ret == -1)
                continue;
            /* If positive return, read OK, break loop */
            if (ret > 0)
                break;
            /*
             * Must be an ASN1 parsing error.
             * Free up any partial choice value
             */
            asn1_template_free(pchptr, tt);
            errtt = tt;
            ERR_raise(ERR_LIB_ASN1, ERR_R_NESTED_ASN1_ERROR);
            goto err;
        }

        /* Did we fall off the end without reading anything? */
        if (i == it->tcount) {
            /* If OPTIONAL, this is OK */
            if (opt) {
                /* Free and zero it */
                ASN1_item_ex_free(pval, it);
                return -1;
            }
            ERR_raise(ERR_LIB_ASN1, ASN1_R_NO_MATCHING_CHOICE_TYPE);
            goto err;
        }

        asn1_set_choice_selector(pval, i, it);

        if (asn1_cb && !asn1_cb(ASN1_OP_D2I_POST, pval, it, NULL))
            goto auxerr;
        *in = p;
        return 1;

    case ASN1_ITYPE_NDEF_SEQUENCE:
    case ASN1_ITYPE_SEQUENCE:
        p = *in;
        tmplen = len;

        /* If no IMPLICIT tagging set to SEQUENCE, UNIVERSAL */
        if (tag == -1) {
            tag = V_ASN1_SEQUENCE;
            aclass = V_ASN1_UNIVERSAL;
        }
        /* Get SEQUENCE length and update len, p */
        ret = asn1_check_tlen(&len, NULL, NULL, &seq_eoc, &cst,
                              &p, len, tag, aclass, opt, ctx);
        if (!ret) {
            ERR_raise(ERR_LIB_ASN1, ERR_R_NESTED_ASN1_ERROR);
            goto err;
        } else if (ret == -1)
            return -1;
        if (aux && (aux->flags & ASN1_AFLG_BROKEN)) {
            len = tmplen - (p - *in);
            seq_nolen = 1;
        }
        /* If indefinite we don't do a length check */
        else
            seq_nolen = seq_eoc;
        if (!cst) {
            ERR_raise(ERR_LIB_ASN1, ASN1_R_SEQUENCE_NOT_CONSTRUCTED);
            goto err;
        }

        if (*pval == NULL && !ASN1_item_ex_new(pval, it)) {
            ERR_raise(ERR_LIB_ASN1, ERR_R_NESTED_ASN1_ERROR);
            goto err;
        }

        if (asn1_cb && !asn1_cb(ASN1_OP_D2I_PRE, pval, it, NULL))
            goto auxerr;

        /* Free up and zero any ADB found */
        for (i = 0, tt = it->templates; i < it->tcount; i++, tt++) {
            if (tt->flags & ASN1_TFLG_ADB_MASK) {
                const ASN1_TEMPLATE *seqtt;
                ASN1_VALUE **pseqval;
                seqtt = asn1_do_adb(*pval, tt, 0);
                if (seqtt == NULL)
                    continue;
                pseqval = asn1_get_field_ptr(pval, seqtt);
                asn1_template_free(pseqval, seqtt);
            }
        }

        /* Get each field entry */
        for (i = 0, tt = it->templates; i < it->tcount; i++, tt++) {
            const ASN1_TEMPLATE *seqtt;
            ASN1_VALUE **pseqval;
            seqtt = asn1_do_adb(*pval, tt, 1);
            if (seqtt == NULL)
                goto err;
            pseqval = asn1_get_field_ptr(pval, seqtt);
            /* Have we ran out of data? */
            if (!len)
                break;
            q = p;
            if (asn1_check_eoc(&p, len)) {
                if (!seq_eoc) {
                    ERR_raise(ERR_LIB_ASN1, ASN1_R_UNEXPECTED_EOC);
                    goto err;
                }
                len -= p - q;
                seq_eoc = 0;
                break;
            }
            /*
             * This determines the OPTIONAL flag value. The field cannot be
             * omitted if it is the last of a SEQUENCE and there is still
             * data to be read. This isn't strictly necessary but it
             * increases efficiency in some cases.
             */
            if (i == (it->tcount - 1))
                isopt = 0;
            else
                isopt = (char)(seqtt->flags & ASN1_TFLG_OPTIONAL);
            /*
             * attempt to read in field, allowing each to be OPTIONAL
             */

            ret = asn1_template_ex_d2i(pseqval, &p, len, seqtt, isopt, ctx,
                                       depth);
            if (!ret) {
                errtt = seqtt;
                goto err;
            } else if (ret == -1) {
                /*
                 * OPTIONAL component absent. Free and zero the field.
                 */
                asn1_template_free(pseqval, seqtt);
                continue;
            }
            /* Update length */
            len -= p - q;
        }

        /* Check for EOC if expecting one */
        if (seq_eoc && !asn1_check_eoc(&p, len)) {
            ERR_raise(ERR_LIB_ASN1, ASN1_R_MISSING_EOC);
            goto err;
        }
        /* Check all data read */
        if (!seq_nolen && len) {
            ERR_raise(ERR_LIB_ASN1, ASN1_R_SEQUENCE_LENGTH_MISMATCH);
            goto err;
        }

        /*
         * If we get here we've got no more data in the SEQUENCE, however we
         * may not have read all fields so check all remaining are OPTIONAL
         * and clear any that are.
         */
        for (; i < it->tcount; tt++, i++) {
            const ASN1_TEMPLATE *seqtt;
            seqtt = asn1_do_adb(*pval, tt, 1);
            if (seqtt == NULL)
                goto err;
            if (seqtt->flags & ASN1_TFLG_OPTIONAL) {
                ASN1_VALUE **pseqval;
                pseqval = asn1_get_field_ptr(pval, seqtt);
                asn1_template_free(pseqval, seqtt);
            } else {
                errtt = seqtt;
                ERR_raise(ERR_LIB_ASN1, ASN1_R_FIELD_MISSING);
                goto err;
            }
        }
        /* Save encoding */
        if (!asn1_enc_save(pval, *in, p - *in, it))
            goto auxerr;
        if (asn1_cb && !asn1_cb(ASN1_OP_D2I_POST, pval, it, NULL))
            goto auxerr;
        *in = p;
        return 1;

    default:
        return 0;
    }
 auxerr:
    ERR_raise(ERR_LIB_ASN1, ASN1_R_AUX_ERROR);
 err:
    if (errtt)
        ERR_add_error_data(4, "Field=", errtt->field_name,
                           ", Type=", it->sname);
    else
        ERR_add_error_data(2, "Type=", it->sname);
    return 0;
}