library/x509write_csr.c

/*
 *  X.509 Certificate Signing Request writing
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed 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.
 */
/*
 * References:
 * - CSRs: PKCS#10 v1.7 aka RFC 2986
 * - attributes: PKCS#9 v2.0 aka RFC 2985
 */

#include "common.h"

#if defined(MBEDTLS_X509_CSR_WRITE_C)

#include "mbedtls/x509.h"
#include "mbedtls/x509_csr.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/error.h"
#include "mbedtls/oid.h"
#include "mbedtls/platform_util.h"

#if defined(MBEDTLS_USE_PSA_CRYPTO)
#include "psa/crypto.h"
#include "mbedtls/psa_util.h"
#include "md_psa.h"
#endif /* MBEDTLS_USE_PSA_CRYPTO */

#include <string.h>
#include <stdlib.h>

#if defined(MBEDTLS_PEM_WRITE_C)
#include "mbedtls/pem.h"
#endif

#include "mbedtls/platform.h"

#define CHECK_OVERFLOW_ADD(a, b) \
    do                         \
    {                           \
        if (a > SIZE_MAX - (b)) \
        { \
            return MBEDTLS_ERR_X509_BAD_INPUT_DATA; \
        }                            \
        a += b; \
    } while (0)

void mbedtls_x509write_csr_init(mbedtls_x509write_csr *ctx)
{
    memset(ctx, 0, sizeof(mbedtls_x509write_csr));
}

void mbedtls_x509write_csr_free(mbedtls_x509write_csr *ctx)
{
    mbedtls_asn1_free_named_data_list(&ctx->subject);
    mbedtls_asn1_free_named_data_list(&ctx->extensions);

    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_x509write_csr));
}

void mbedtls_x509write_csr_set_md_alg(mbedtls_x509write_csr *ctx, mbedtls_md_type_t md_alg)
{
    ctx->md_alg = md_alg;
}

void mbedtls_x509write_csr_set_key(mbedtls_x509write_csr *ctx, mbedtls_pk_context *key)
{
    ctx->key = key;
}

int mbedtls_x509write_csr_set_subject_name(mbedtls_x509write_csr *ctx,
                                           const char *subject_name)
{
    return mbedtls_x509_string_to_names(&ctx->subject, subject_name);
}

int mbedtls_x509write_csr_set_extension(mbedtls_x509write_csr *ctx,
                                        const char *oid, size_t oid_len,
                                        int critical,
                                        const unsigned char *val, size_t val_len)
{
    return mbedtls_x509_set_extension(&ctx->extensions, oid, oid_len,
                                      critical, val, val_len);
}

int mbedtls_x509write_csr_set_subject_alternative_name(mbedtls_x509write_csr *ctx,
                                                       const mbedtls_x509_san_list *san_list)
{
    int ret = 0;
    const mbedtls_x509_san_list *cur;
    unsigned char *buf;
    unsigned char *p;
    size_t len;
    size_t buflen = 0;

    /* Determine the maximum size of the SubjectAltName list */
    for (cur = san_list; cur != NULL; cur = cur->next) {
        /* Calculate size of the required buffer */
        switch (cur->node.type) {
            case MBEDTLS_X509_SAN_DNS_NAME:
            case MBEDTLS_X509_SAN_UNIFORM_RESOURCE_IDENTIFIER:
            case MBEDTLS_X509_SAN_IP_ADDRESS:
            case MBEDTLS_X509_SAN_RFC822_NAME:
                /* length of value for each name entry,
                 * maximum 4 bytes for the length field,
                 * 1 byte for the tag/type.
                 */
                CHECK_OVERFLOW_ADD(buflen, cur->node.san.unstructured_name.len);
                CHECK_OVERFLOW_ADD(buflen, 4 + 1);
                break;
            case MBEDTLS_X509_SAN_DIRECTORY_NAME:
            {
                const mbedtls_asn1_named_data *chunk = &cur->node.san.directory_name;
                while (chunk != NULL) {
                    // Max 4 bytes for length, +1 for tag,
                    // additional 4 max for length, +1 for tag.
                    // See x509_write_name for more information.
                    CHECK_OVERFLOW_ADD(buflen, 4 + 1 + 4 + 1);
                    CHECK_OVERFLOW_ADD(buflen, chunk->oid.len);
                    CHECK_OVERFLOW_ADD(buflen, chunk->val.len);
                    chunk = chunk->next;
                }
                CHECK_OVERFLOW_ADD(buflen, 4 + 1);
                break;
            }
            default:
                /* Not supported - return. */
                return MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE;
        }
    }

    /* Add the extra length field and tag */
    CHECK_OVERFLOW_ADD(buflen, 4 + 1);

    /* Allocate buffer */
    buf = mbedtls_calloc(1, buflen);
    if (buf == NULL) {
        return MBEDTLS_ERR_ASN1_ALLOC_FAILED;
    }
    p = buf + buflen;

    /* Write ASN.1-based structure */
    cur = san_list;
    len = 0;
    while (cur != NULL) {
        size_t single_san_len = 0;
        switch (cur->node.type) {
            case MBEDTLS_X509_SAN_DNS_NAME:
            case MBEDTLS_X509_SAN_RFC822_NAME:
            case MBEDTLS_X509_SAN_UNIFORM_RESOURCE_IDENTIFIER:
            case MBEDTLS_X509_SAN_IP_ADDRESS:
            {
                const unsigned char *unstructured_name =
                    (const unsigned char *) cur->node.san.unstructured_name.p;
                size_t unstructured_name_len = cur->node.san.unstructured_name.len;

                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len,
                                             mbedtls_asn1_write_raw_buffer(
                                                 &p, buf,
                                                 unstructured_name, unstructured_name_len));
                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len, mbedtls_asn1_write_len(
                                                 &p, buf, unstructured_name_len));
                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len,
                                             mbedtls_asn1_write_tag(
                                                 &p, buf,
                                                 MBEDTLS_ASN1_CONTEXT_SPECIFIC | cur->node.type));
            }
            break;
            case MBEDTLS_X509_SAN_DIRECTORY_NAME:
                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len,
                                             mbedtls_x509_write_names(&p, buf,
                                                                      (mbedtls_asn1_named_data *) &
                                                                      cur->node
                                                                      .san.directory_name));
                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len,
                                             mbedtls_asn1_write_len(&p, buf, single_san_len));
                MBEDTLS_ASN1_CHK_CLEANUP_ADD(single_san_len,
                                             mbedtls_asn1_write_tag(&p, buf,
                                                                    MBEDTLS_ASN1_CONTEXT_SPECIFIC |
                                                                    MBEDTLS_ASN1_CONSTRUCTED |
                                                                    MBEDTLS_X509_SAN_DIRECTORY_NAME));
                break;
            default:
                /* Error out on an unsupported SAN */
                ret = MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE;
                goto cleanup;
        }
        cur = cur->next;
        /* check for overflow */
        if (len > SIZE_MAX - single_san_len) {
            ret = MBEDTLS_ERR_X509_BAD_INPUT_DATA;
            goto cleanup;
        }
        len += single_san_len;
    }

    MBEDTLS_ASN1_CHK_CLEANUP_ADD(len, mbedtls_asn1_write_len(&p, buf, len));
    MBEDTLS_ASN1_CHK_CLEANUP_ADD(len,
                                 mbedtls_asn1_write_tag(&p, buf,
                                                        MBEDTLS_ASN1_CONSTRUCTED |
                                                        MBEDTLS_ASN1_SEQUENCE));

    ret = mbedtls_x509write_csr_set_extension(
        ctx,
        MBEDTLS_OID_SUBJECT_ALT_NAME,
        MBEDTLS_OID_SIZE(MBEDTLS_OID_SUBJECT_ALT_NAME),
        0,
        buf + buflen - len,
        len);

    /* If we exceeded the allocated buffer it means that maximum size of the SubjectAltName list
     * was incorrectly calculated and memory is corrupted. */
    if (p < buf) {
        ret = MBEDTLS_ERR_ASN1_LENGTH_MISMATCH;
    }

cleanup:
    mbedtls_free(buf);
    return ret;
}

int mbedtls_x509write_csr_set_key_usage(mbedtls_x509write_csr *ctx, unsigned char key_usage)
{
    unsigned char buf[4] = { 0 };
    unsigned char *c;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    c = buf + 4;

    ret = mbedtls_asn1_write_named_bitstring(&c, buf, &key_usage, 8);
    if (ret < 3 || ret > 4) {
        return ret;
    }

    ret = mbedtls_x509write_csr_set_extension(ctx, MBEDTLS_OID_KEY_USAGE,
                                              MBEDTLS_OID_SIZE(MBEDTLS_OID_KEY_USAGE),
                                              0, c, (size_t) ret);
    if (ret != 0) {
        return ret;
    }

    return 0;
}

int mbedtls_x509write_csr_set_ns_cert_type(mbedtls_x509write_csr *ctx,
                                           unsigned char ns_cert_type)
{
    unsigned char buf[4] = { 0 };
    unsigned char *c;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    c = buf + 4;

    ret = mbedtls_asn1_write_named_bitstring(&c, buf, &ns_cert_type, 8);
    if (ret < 3 || ret > 4) {
        return ret;
    }

    ret = mbedtls_x509write_csr_set_extension(ctx, MBEDTLS_OID_NS_CERT_TYPE,
                                              MBEDTLS_OID_SIZE(MBEDTLS_OID_NS_CERT_TYPE),
                                              0, c, (size_t) ret);
    if (ret != 0) {
        return ret;
    }

    return 0;
}

static int x509write_csr_der_internal(mbedtls_x509write_csr *ctx,
                                      unsigned char *buf,
                                      size_t size,
                                      unsigned char *sig, size_t sig_size,
                                      int (*f_rng)(void *, unsigned char *, size_t),
                                      void *p_rng)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const char *sig_oid;
    size_t sig_oid_len = 0;
    unsigned char *c, *c2;
    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
    size_t pub_len = 0, sig_and_oid_len = 0, sig_len;
    size_t len = 0;
    mbedtls_pk_type_t pk_alg;
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    size_t hash_len;
    psa_algorithm_t hash_alg = mbedtls_md_psa_alg_from_type(ctx->md_alg);
#endif /* MBEDTLS_USE_PSA_CRYPTO */

    /* Write the CSR backwards starting from the end of buf */
    c = buf + size;

    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_x509_write_extensions(&c, buf,
                                                            ctx->extensions));

    if (len) {
        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
        MBEDTLS_ASN1_CHK_ADD(len,
                             mbedtls_asn1_write_tag(
                                 &c, buf,
                                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));

        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
        MBEDTLS_ASN1_CHK_ADD(len,
                             mbedtls_asn1_write_tag(
                                 &c, buf,
                                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET));

        MBEDTLS_ASN1_CHK_ADD(len,
                             mbedtls_asn1_write_oid(
                                 &c, buf, MBEDTLS_OID_PKCS9_CSR_EXT_REQ,
                                 MBEDTLS_OID_SIZE(MBEDTLS_OID_PKCS9_CSR_EXT_REQ)));

        MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
        MBEDTLS_ASN1_CHK_ADD(len,
                             mbedtls_asn1_write_tag(
                                 &c, buf,
                                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));
    }

    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
    MBEDTLS_ASN1_CHK_ADD(len,
                         mbedtls_asn1_write_tag(
                             &c, buf,
                             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC));

    MBEDTLS_ASN1_CHK_ADD(pub_len, mbedtls_pk_write_pubkey_der(ctx->key,
                                                              buf, c - buf));
    c -= pub_len;
    len += pub_len;

    /*
     *  Subject  ::=  Name
     */
    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_x509_write_names(&c, buf,
                                                       ctx->subject));

    /*
     *  Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
     */
    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_int(&c, buf, 0));

    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c, buf, len));
    MBEDTLS_ASN1_CHK_ADD(len,
                         mbedtls_asn1_write_tag(
                             &c, buf,
                             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));

    /*
     * Sign the written CSR data into the sig buffer
     * Note: hash errors can happen only after an internal error
     */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if (psa_hash_compute(hash_alg,
                         c,
                         len,
                         hash,
                         sizeof(hash),
                         &hash_len) != PSA_SUCCESS) {
        return MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED;
    }
#else /* MBEDTLS_USE_PSA_CRYPTO */
    ret = mbedtls_md(mbedtls_md_info_from_type(ctx->md_alg), c, len, hash);
    if (ret != 0) {
        return ret;
    }
#endif
    if ((ret = mbedtls_pk_sign(ctx->key, ctx->md_alg, hash, 0,
                               sig, sig_size, &sig_len,
                               f_rng, p_rng)) != 0) {
        return ret;
    }

    if (mbedtls_pk_can_do(ctx->key, MBEDTLS_PK_RSA)) {
        pk_alg = MBEDTLS_PK_RSA;
    } else if (mbedtls_pk_can_do(ctx->key, MBEDTLS_PK_ECDSA)) {
        pk_alg = MBEDTLS_PK_ECDSA;
    } else {
        return MBEDTLS_ERR_X509_INVALID_ALG;
    }

    if ((ret = mbedtls_oid_get_oid_by_sig_alg(pk_alg, ctx->md_alg,
                                              &sig_oid, &sig_oid_len)) != 0) {
        return ret;
    }

    /*
     * Move the written CSR data to the start of buf to create space for
     * writing the signature into buf.
     */
    memmove(buf, c, len);

    /*
     * Write sig and its OID into buf backwards from the end of buf.
     * Note: mbedtls_x509_write_sig will check for c2 - ( buf + len ) < sig_len
     * and return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL if needed.
     */
    c2 = buf + size;
    MBEDTLS_ASN1_CHK_ADD(sig_and_oid_len,
                         mbedtls_x509_write_sig(&c2, buf + len, sig_oid, sig_oid_len,
                                                sig, sig_len));

    /*
     * Compact the space between the CSR data and signature by moving the
     * CSR data to the start of the signature.
     */
    c2 -= len;
    memmove(c2, buf, len);

    /* ASN encode the total size and tag the CSR data with it. */
    len += sig_and_oid_len;
    MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(&c2, buf, len));
    MBEDTLS_ASN1_CHK_ADD(len,
                         mbedtls_asn1_write_tag(
                             &c2, buf,
                             MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE));

    /* Zero the unused bytes at the start of buf */
    memset(buf, 0, c2 - buf);

    return (int) len;
}

int mbedtls_x509write_csr_der(mbedtls_x509write_csr *ctx, unsigned char *buf,
                              size_t size,
                              int (*f_rng)(void *, unsigned char *, size_t),
                              void *p_rng)
{
    int ret;
    unsigned char *sig;

    if ((sig = mbedtls_calloc(1, MBEDTLS_PK_SIGNATURE_MAX_SIZE)) == NULL) {
        return MBEDTLS_ERR_X509_ALLOC_FAILED;
    }

    ret = x509write_csr_der_internal(ctx, buf, size,
                                     sig, MBEDTLS_PK_SIGNATURE_MAX_SIZE,
                                     f_rng, p_rng);

    mbedtls_free(sig);

    return ret;
}

#define PEM_BEGIN_CSR           "-----BEGIN CERTIFICATE REQUEST-----\n"
#define PEM_END_CSR             "-----END CERTIFICATE REQUEST-----\n"

#if defined(MBEDTLS_PEM_WRITE_C)
int mbedtls_x509write_csr_pem(mbedtls_x509write_csr *ctx, unsigned char *buf, size_t size,
                              int (*f_rng)(void *, unsigned char *, size_t),
                              void *p_rng)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t olen = 0;

    if ((ret = mbedtls_x509write_csr_der(ctx, buf, size,
                                         f_rng, p_rng)) < 0) {
        return ret;
    }

    if ((ret = mbedtls_pem_write_buffer(PEM_BEGIN_CSR, PEM_END_CSR,
                                        buf + size - ret,
                                        ret, buf, size, &olen)) != 0) {
        return ret;
    }

    return 0;
}
#endif /* MBEDTLS_PEM_WRITE_C */

#endif /* MBEDTLS_X509_CSR_WRITE_C */