esp-idf/components/mbedtls/port/dynamic/esp_mbedtls_dynamic_impl.c

/*
 * SPDX-FileCopyrightText: 2020-2022 Espressif Systems (Shanghai) CO LTD
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <string.h>
#include "esp_mbedtls_dynamic_impl.h"

#define COUNTER_SIZE (8)
#define CACHE_IV_SIZE (16)
#define CACHE_BUFFER_SIZE (CACHE_IV_SIZE + COUNTER_SIZE)

#define TX_IDLE_BUFFER_SIZE (MBEDTLS_SSL_HEADER_LEN + CACHE_BUFFER_SIZE)

static const char *TAG = "Dynamic Impl";

static void esp_mbedtls_set_buf_state(unsigned char *buf, esp_mbedtls_ssl_buf_states state)
{
    struct esp_mbedtls_ssl_buf *temp = __containerof(buf, struct esp_mbedtls_ssl_buf, buf[0]);
    temp->state = state;
}

static esp_mbedtls_ssl_buf_states esp_mbedtls_get_buf_state(unsigned char *buf)
{
    struct esp_mbedtls_ssl_buf *temp = __containerof(buf, struct esp_mbedtls_ssl_buf, buf[0]);
    return temp->state;
}

void esp_mbedtls_free_buf(unsigned char *buf)
{
    struct esp_mbedtls_ssl_buf *temp = __containerof(buf, struct esp_mbedtls_ssl_buf, buf[0]);
    ESP_LOGV(TAG, "free buffer @ %p", temp);
    mbedtls_free(temp);
}

static void esp_mbedtls_init_ssl_buf(struct esp_mbedtls_ssl_buf *buf, unsigned int len)
{
    if (buf) {
        buf->state = ESP_MBEDTLS_SSL_BUF_CACHED;
        buf->len = len;
    }
}

static void esp_mbedtls_parse_record_header(mbedtls_ssl_context *ssl)
{
    ssl->MBEDTLS_PRIVATE(in_msgtype) =  ssl->MBEDTLS_PRIVATE(in_hdr)[0];
    ssl->MBEDTLS_PRIVATE(in_msglen) = (ssl->MBEDTLS_PRIVATE(in_len)[0] << 8) | ssl->MBEDTLS_PRIVATE(in_len)[1];
}

static int tx_buffer_len(mbedtls_ssl_context *ssl, int len)
{
    (void)ssl;

    if (!len) {
        return MBEDTLS_SSL_OUT_BUFFER_LEN;
    } else {
        return len + MBEDTLS_SSL_HEADER_LEN
                   + MBEDTLS_MAX_IV_LENGTH
                   + MBEDTLS_SSL_MAC_ADD
                   + MBEDTLS_SSL_PADDING_ADD
                   + MBEDTLS_SSL_MAX_CID_EXPANSION;
    }
}

static void init_tx_buffer(mbedtls_ssl_context *ssl, unsigned char *buf)
{
    /**
     * In mbedtls, ssl->MBEDTLS_PRIVATE(out_msg) = ssl->MBEDTLS_PRIVATE(out_buf) + offset;
     */
    if (!buf) {
        int out_msg_off = (int)ssl->MBEDTLS_PRIVATE(out_msg) - (int)ssl->MBEDTLS_PRIVATE(out_buf);

        if (!out_msg_off) {
            out_msg_off = MBEDTLS_SSL_HEADER_LEN;
        }

        ssl->MBEDTLS_PRIVATE(out_buf) = NULL;
        ssl->MBEDTLS_PRIVATE(out_ctr) = NULL;
        ssl->MBEDTLS_PRIVATE(out_hdr) = NULL;
        ssl->MBEDTLS_PRIVATE(out_len) = NULL;
        ssl->MBEDTLS_PRIVATE(out_iv)  = NULL;
        ssl->MBEDTLS_PRIVATE(out_msg) = (unsigned char *)out_msg_off;
    } else {
        int out_msg_off = (int)ssl->MBEDTLS_PRIVATE(out_msg);

        ssl->MBEDTLS_PRIVATE(out_buf) = buf;
        ssl->MBEDTLS_PRIVATE(out_ctr) = ssl->MBEDTLS_PRIVATE(out_buf);
        ssl->MBEDTLS_PRIVATE(out_hdr) = ssl->MBEDTLS_PRIVATE(out_buf) +  8;
        ssl->MBEDTLS_PRIVATE(out_len) = ssl->MBEDTLS_PRIVATE(out_buf) + 11;
        ssl->MBEDTLS_PRIVATE(out_iv)  = ssl->MBEDTLS_PRIVATE(out_buf) + MBEDTLS_SSL_HEADER_LEN;
        ssl->MBEDTLS_PRIVATE(out_msg) = ssl->MBEDTLS_PRIVATE(out_buf) + out_msg_off;

        ESP_LOGV(TAG, "out msg offset is %d", out_msg_off);
    }

    ssl->MBEDTLS_PRIVATE(out_msgtype) = 0;
    ssl->MBEDTLS_PRIVATE(out_msglen) = 0;
    ssl->MBEDTLS_PRIVATE(out_left) = 0;
}

static void init_rx_buffer(mbedtls_ssl_context *ssl, unsigned char *buf)
{
    /**
     * In mbedtls, ssl->MBEDTLS_PRIVATE(in_msg) = ssl->MBEDTLS_PRIVATE(in_buf) + offset;
     */
    if (!buf) {
        int in_msg_off = (int)ssl->MBEDTLS_PRIVATE(in_msg) - (int)ssl->MBEDTLS_PRIVATE(in_buf);

        if (!in_msg_off) {
            in_msg_off = MBEDTLS_SSL_HEADER_LEN;
        }

        ssl->MBEDTLS_PRIVATE(in_buf) = NULL;
        ssl->MBEDTLS_PRIVATE(in_ctr) = NULL;
        ssl->MBEDTLS_PRIVATE(in_hdr) = NULL;
        ssl->MBEDTLS_PRIVATE(in_len) = NULL;
        ssl->MBEDTLS_PRIVATE(in_iv)  = NULL;
        ssl->MBEDTLS_PRIVATE(in_msg) = (unsigned char *)in_msg_off;
    } else {
        int in_msg_off = (int)ssl->MBEDTLS_PRIVATE(in_msg);

        ssl->MBEDTLS_PRIVATE(in_buf) = buf;
        ssl->MBEDTLS_PRIVATE(in_ctr) = ssl->MBEDTLS_PRIVATE(in_buf);
        ssl->MBEDTLS_PRIVATE(in_hdr) = ssl->MBEDTLS_PRIVATE(in_buf) +  8;
        ssl->MBEDTLS_PRIVATE(in_len) = ssl->MBEDTLS_PRIVATE(in_buf) + 11;
        ssl->MBEDTLS_PRIVATE(in_iv)  = ssl->MBEDTLS_PRIVATE(in_buf) + MBEDTLS_SSL_HEADER_LEN;
        ssl->MBEDTLS_PRIVATE(in_msg) = ssl->MBEDTLS_PRIVATE(in_buf) + in_msg_off;

        ESP_LOGV(TAG, "in msg offset is %d", in_msg_off);
    }

    ssl->MBEDTLS_PRIVATE(in_msgtype) = 0;
    ssl->MBEDTLS_PRIVATE(in_msglen) = 0;
    ssl->MBEDTLS_PRIVATE(in_left) = 0;
}

static int esp_mbedtls_alloc_tx_buf(mbedtls_ssl_context *ssl, int len)
{
    struct esp_mbedtls_ssl_buf *esp_buf;

    if (ssl->MBEDTLS_PRIVATE(out_buf)) {
        esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(out_buf));
        ssl->MBEDTLS_PRIVATE(out_buf) = NULL;
    }

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + len);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%d bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + len);
        return MBEDTLS_ERR_SSL_ALLOC_FAILED;
    }

    ESP_LOGV(TAG, "add out buffer %d bytes @ %p", len, esp_buf->buf);

    esp_mbedtls_init_ssl_buf(esp_buf, len);
    /**
     * Mark the out_msg offset from ssl->MBEDTLS_PRIVATE(out_buf).
     *
     * In mbedtls, ssl->MBEDTLS_PRIVATE(out_msg) = ssl->MBEDTLS_PRIVATE(out_buf) + offset;
     */
    ssl->MBEDTLS_PRIVATE(out_msg) = (unsigned char *)MBEDTLS_SSL_HEADER_LEN;

    init_tx_buffer(ssl, esp_buf->buf);

    return 0;
}

int esp_mbedtls_setup_tx_buffer(mbedtls_ssl_context *ssl)
{
    CHECK_OK(esp_mbedtls_alloc_tx_buf(ssl, TX_IDLE_BUFFER_SIZE));

    /* mark the out buffer has no data cached */
    esp_mbedtls_set_buf_state(ssl->MBEDTLS_PRIVATE(out_buf), ESP_MBEDTLS_SSL_BUF_NO_CACHED);

    return 0;
}

void esp_mbedtls_setup_rx_buffer(mbedtls_ssl_context *ssl)
{
    ssl->MBEDTLS_PRIVATE(in_msg) = ssl->MBEDTLS_PRIVATE(in_buf) = NULL;
    init_rx_buffer(ssl, NULL);
}

int esp_mbedtls_reset_add_tx_buffer(mbedtls_ssl_context *ssl)
{
    return esp_mbedtls_alloc_tx_buf(ssl, MBEDTLS_SSL_OUT_BUFFER_LEN);
}

int esp_mbedtls_reset_free_tx_buffer(mbedtls_ssl_context *ssl)
{
    esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(out_buf));
    init_tx_buffer(ssl, NULL);

    CHECK_OK(esp_mbedtls_setup_tx_buffer(ssl));

    return 0;
}

int esp_mbedtls_reset_add_rx_buffer(mbedtls_ssl_context *ssl)
{
    struct esp_mbedtls_ssl_buf *esp_buf;

    if (ssl->MBEDTLS_PRIVATE(in_buf)) {
        esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(in_buf));
        ssl->MBEDTLS_PRIVATE(in_buf) = NULL;
    }

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + MBEDTLS_SSL_IN_BUFFER_LEN);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%d bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + MBEDTLS_SSL_IN_BUFFER_LEN);
        return MBEDTLS_ERR_SSL_ALLOC_FAILED;
    }

    ESP_LOGV(TAG, "add in buffer %d bytes @ %p", MBEDTLS_SSL_IN_BUFFER_LEN, esp_buf->buf);

    esp_mbedtls_init_ssl_buf(esp_buf, MBEDTLS_SSL_IN_BUFFER_LEN);
    /**
     * Mark the in_msg offset from ssl->MBEDTLS_PRIVATE(in_buf).
     *
     * In mbedtls, ssl->MBEDTLS_PRIVATE(in_msg) = ssl->MBEDTLS_PRIVATE(in_buf) + offset;
     */
    ssl->MBEDTLS_PRIVATE(in_msg) = (unsigned char *)MBEDTLS_SSL_HEADER_LEN;

    init_rx_buffer(ssl, esp_buf->buf);

    return 0;
}

void esp_mbedtls_reset_free_rx_buffer(mbedtls_ssl_context *ssl)
{
    esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(in_buf));
    init_rx_buffer(ssl, NULL);
}

int esp_mbedtls_add_tx_buffer(mbedtls_ssl_context *ssl, size_t buffer_len)
{
    int ret = 0;
    int cached = 0;
    struct esp_mbedtls_ssl_buf *esp_buf;
    unsigned char cache_buf[CACHE_BUFFER_SIZE];

    ESP_LOGV(TAG, "--> add out");

    if (ssl->MBEDTLS_PRIVATE(out_buf)) {
        if (esp_mbedtls_get_buf_state(ssl->MBEDTLS_PRIVATE(out_buf)) == ESP_MBEDTLS_SSL_BUF_CACHED) {
            ESP_LOGV(TAG, "out buffer is not empty");
            ret = 0;
            goto exit;
        } else {
            memcpy(cache_buf, ssl->MBEDTLS_PRIVATE(out_buf), CACHE_BUFFER_SIZE);
            esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(out_buf));
            init_tx_buffer(ssl, NULL);
            cached = 1;
        }
    }

    buffer_len = tx_buffer_len(ssl, buffer_len);

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + buffer_len);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%zu bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + buffer_len);
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }

    ESP_LOGV(TAG, "add out buffer %zu bytes @ %p", buffer_len, esp_buf->buf);

    esp_mbedtls_init_ssl_buf(esp_buf, buffer_len);
    init_tx_buffer(ssl, esp_buf->buf);

    if (cached) {
        memcpy(ssl->MBEDTLS_PRIVATE(out_ctr), cache_buf, COUNTER_SIZE);
        memcpy(ssl->MBEDTLS_PRIVATE(out_iv), cache_buf + COUNTER_SIZE, CACHE_IV_SIZE);
    }

    ESP_LOGV(TAG, "ssl->MBEDTLS_PRIVATE(out_buf)=%p ssl->MBEDTLS_PRIVATE(out_msg)=%p", ssl->MBEDTLS_PRIVATE(out_buf), ssl->MBEDTLS_PRIVATE(out_msg));

exit:
    ESP_LOGV(TAG, "<-- add out");

    return ret;
}


int esp_mbedtls_free_tx_buffer(mbedtls_ssl_context *ssl)
{
    int ret = 0;
    unsigned char buf[CACHE_BUFFER_SIZE];
    struct esp_mbedtls_ssl_buf *esp_buf;

    ESP_LOGV(TAG, "--> free out");

    if (!ssl->MBEDTLS_PRIVATE(out_buf) || (ssl->MBEDTLS_PRIVATE(out_buf) && (esp_mbedtls_get_buf_state(ssl->MBEDTLS_PRIVATE(out_buf)) == ESP_MBEDTLS_SSL_BUF_NO_CACHED))) {
        ret = 0;
        goto exit;
    }

    memcpy(buf, ssl->MBEDTLS_PRIVATE(out_ctr), COUNTER_SIZE);
    memcpy(buf + COUNTER_SIZE, ssl->MBEDTLS_PRIVATE(out_iv), CACHE_IV_SIZE);

    esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(out_buf));
    init_tx_buffer(ssl, NULL);

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + TX_IDLE_BUFFER_SIZE);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%d bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + TX_IDLE_BUFFER_SIZE);
        return MBEDTLS_ERR_SSL_ALLOC_FAILED;
    }

    esp_mbedtls_init_ssl_buf(esp_buf, TX_IDLE_BUFFER_SIZE);
    memcpy(esp_buf->buf, buf, CACHE_BUFFER_SIZE);
    init_tx_buffer(ssl, esp_buf->buf);
    esp_mbedtls_set_buf_state(ssl->MBEDTLS_PRIVATE(out_buf), ESP_MBEDTLS_SSL_BUF_NO_CACHED);
exit:
    ESP_LOGV(TAG, "<-- free out");

    return ret;
}

int esp_mbedtls_add_rx_buffer(mbedtls_ssl_context *ssl)
{
    int cached = 0;
    int ret = 0;
    int buffer_len;
    struct esp_mbedtls_ssl_buf *esp_buf;
    unsigned char cache_buf[16];
    unsigned char msg_head[5];
    size_t in_msglen, in_left;

    ESP_LOGV(TAG, "--> add rx");

    if (ssl->MBEDTLS_PRIVATE(in_buf)) {
        if (esp_mbedtls_get_buf_state(ssl->MBEDTLS_PRIVATE(in_buf)) == ESP_MBEDTLS_SSL_BUF_CACHED) {
            ESP_LOGV(TAG, "in buffer is not empty");
            ret = 0;
            goto exit;
        } else {
            cached = 1;
        }
    }

    ssl->MBEDTLS_PRIVATE(in_hdr) = msg_head;
    ssl->MBEDTLS_PRIVATE(in_len) = msg_head + 3;

    if ((ret = mbedtls_ssl_fetch_input(ssl, mbedtls_ssl_in_hdr_len(ssl))) != 0) {
        if (ret == MBEDTLS_ERR_SSL_TIMEOUT) {
            ESP_LOGD(TAG, "mbedtls_ssl_fetch_input reads data times out");
        } else if (ret == MBEDTLS_ERR_SSL_WANT_READ) {
            ESP_LOGD(TAG, "mbedtls_ssl_fetch_input wants to read more data");
        } else {
            ESP_LOGE(TAG, "mbedtls_ssl_fetch_input error=%d", -ret);
        }

        goto exit;
    }

    esp_mbedtls_parse_record_header(ssl);

    in_left = ssl->MBEDTLS_PRIVATE(in_left);
    in_msglen = ssl->MBEDTLS_PRIVATE(in_msglen);
    buffer_len = tx_buffer_len(ssl, in_msglen);

    ESP_LOGV(TAG, "message length is %d RX buffer length should be %d left is %d",
                (int)in_msglen, (int)buffer_len, (int)ssl->MBEDTLS_PRIVATE(in_left));

    if (cached) {
        memcpy(cache_buf, ssl->MBEDTLS_PRIVATE(in_buf), 16);
        esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(in_buf));
        init_rx_buffer(ssl, NULL);
    }

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + buffer_len);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%d bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + buffer_len);
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }

    ESP_LOGV(TAG, "add in buffer %d bytes @ %p", buffer_len, esp_buf->buf);

    esp_mbedtls_init_ssl_buf(esp_buf, buffer_len);
    init_rx_buffer(ssl, esp_buf->buf);

    if (cached) {
        memcpy(ssl->MBEDTLS_PRIVATE(in_ctr), cache_buf, 8);
        memcpy(ssl->MBEDTLS_PRIVATE(in_iv), cache_buf + 8, 8);
    }

    memcpy(ssl->MBEDTLS_PRIVATE(in_hdr), msg_head, in_left);
    ssl->MBEDTLS_PRIVATE(in_left) = in_left;
    ssl->MBEDTLS_PRIVATE(in_msglen) = 0;

exit:
    ESP_LOGV(TAG, "<-- add rx");

    return ret;
}

int esp_mbedtls_free_rx_buffer(mbedtls_ssl_context *ssl)
{
    int ret = 0;
    unsigned char buf[16];
    struct esp_mbedtls_ssl_buf *esp_buf;

    ESP_LOGV(TAG, "--> free rx");

    /**
     * When have read multi messages once, can't free the input buffer directly.
     */
    if (!ssl->MBEDTLS_PRIVATE(in_buf) || (ssl->MBEDTLS_PRIVATE(in_hslen) && (ssl->MBEDTLS_PRIVATE(in_hslen) < ssl->MBEDTLS_PRIVATE(in_msglen))) ||
        (ssl->MBEDTLS_PRIVATE(in_buf) && (esp_mbedtls_get_buf_state(ssl->MBEDTLS_PRIVATE(in_buf)) == ESP_MBEDTLS_SSL_BUF_NO_CACHED))) {
        ret = 0;
        goto exit;
    }

    /**
     * The previous processing is just skipped, so "ssl->MBEDTLS_PRIVATE(in_msglen) = 0"
     */
    if (!ssl->MBEDTLS_PRIVATE(in_msgtype)) {
        goto exit;
    }

    memcpy(buf, ssl->MBEDTLS_PRIVATE(in_ctr), 8);
    memcpy(buf + 8, ssl->MBEDTLS_PRIVATE(in_iv), 8);

    esp_mbedtls_free_buf(ssl->MBEDTLS_PRIVATE(in_buf));
    init_rx_buffer(ssl, NULL);

    esp_buf = mbedtls_calloc(1, SSL_BUF_HEAD_OFFSET_SIZE + 16);
    if (!esp_buf) {
        ESP_LOGE(TAG, "alloc(%d bytes) failed", SSL_BUF_HEAD_OFFSET_SIZE + 16);
        ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
        goto exit;
    }

    esp_mbedtls_init_ssl_buf(esp_buf, 16);
    memcpy(esp_buf->buf, buf, 16);
    init_rx_buffer(ssl, esp_buf->buf);
    esp_mbedtls_set_buf_state(ssl->MBEDTLS_PRIVATE(in_buf), ESP_MBEDTLS_SSL_BUF_NO_CACHED);
exit:
    ESP_LOGV(TAG, "<-- free rx");

    return ret;
}

size_t esp_mbedtls_get_crt_size(mbedtls_x509_crt *cert, size_t *num)
{
    size_t n = 0;
    size_t bytes = 0;

    while (cert) {
        bytes += cert->MBEDTLS_PRIVATE(raw).MBEDTLS_PRIVATE(len);
        n++;

        cert = cert->MBEDTLS_PRIVATE(next);
    }

    *num = n;

    return bytes;
}

#ifdef CONFIG_MBEDTLS_DYNAMIC_FREE_CONFIG_DATA
void esp_mbedtls_free_dhm(mbedtls_ssl_context *ssl)
{
#ifdef CONFIG_MBEDTLS_DHM_C
    mbedtls_mpi_free((mbedtls_mpi *)&ssl->MBEDTLS_PRIVATE(conf)->MBEDTLS_PRIVATE(dhm_P));
    mbedtls_mpi_free((mbedtls_mpi *)&ssl->MBEDTLS_PRIVATE(conf)->MBEDTLS_PRIVATE(dhm_G));
#endif /* CONFIG_MBEDTLS_DHM_C */
}

void esp_mbedtls_free_keycert(mbedtls_ssl_context *ssl)
{
    mbedtls_ssl_config *conf = (mbedtls_ssl_config *)ssl->MBEDTLS_PRIVATE(conf);
    mbedtls_ssl_key_cert *keycert = conf->MBEDTLS_PRIVATE(key_cert), *next;

    while (keycert) {
        next = keycert->next;

        if (keycert) {
            mbedtls_free(keycert);
        }

        keycert = next;
    }

    conf->MBEDTLS_PRIVATE(key_cert) = NULL;
}

void esp_mbedtls_free_keycert_key(mbedtls_ssl_context *ssl)
{
    mbedtls_ssl_key_cert *keycert = ssl->MBEDTLS_PRIVATE(conf)->MBEDTLS_PRIVATE(key_cert);

    while (keycert) {
        if (keycert->key) {
            mbedtls_pk_free(keycert->key);
            keycert->key = NULL;
        }
        keycert = keycert->next;
    }
}

void esp_mbedtls_free_keycert_cert(mbedtls_ssl_context *ssl)
{
    mbedtls_ssl_key_cert *keycert = ssl->MBEDTLS_PRIVATE(conf)->MBEDTLS_PRIVATE(key_cert);

    while (keycert) {
        if (keycert->cert) {
            mbedtls_x509_crt_free(keycert->cert);
            keycert->cert = NULL;
        }
        keycert = keycert->next;
    }
}
#endif /* CONFIG_MBEDTLS_DYNAMIC_FREE_CONFIG_DATA */

#ifdef CONFIG_MBEDTLS_DYNAMIC_FREE_CA_CERT
void esp_mbedtls_free_cacert(mbedtls_ssl_context *ssl)
{
    if (ssl->MBEDTLS_PRIVATE(conf)->MBEDTLS_PRIVATE(ca_chain)) {
        mbedtls_ssl_config *conf = (mbedtls_ssl_config *)ssl->MBEDTLS_PRIVATE(conf);

        mbedtls_x509_crt_free(conf->MBEDTLS_PRIVATE(ca_chain));
        conf->MBEDTLS_PRIVATE(ca_chain) = NULL;
    }
}
#endif /* CONFIG_MBEDTLS_DYNAMIC_FREE_CA_CERT */