copy esp_crt_bundle.c from esp-idf@d51f7d8821

Author: jepler

ports/raspberrypi/mbedtls/esp_crt_bundle.c

@@ -0,0 +1,251 @@
+// Copyright 2018-2019 Espressif Systems (Shanghai) PTE LTD
+//
+// 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.
+
+
+#include <string.h>
+#include <esp_system.h>
+#include "esp_crt_bundle.h"
+#include "esp_log.h"
+
+#define BUNDLE_HEADER_OFFSET 2
+#define CRT_HEADER_OFFSET 4
+
+static const char *TAG = "esp-x509-crt-bundle";
+
+/* a dummy certificate so that
+ * cacert_ptr passes non-NULL check during handshake */
+static mbedtls_x509_crt s_dummy_crt;
+
+
+extern const uint8_t x509_crt_imported_bundle_bin_start[] asm("_binary_x509_crt_bundle_start");
+extern const uint8_t x509_crt_imported_bundle_bin_end[]   asm("_binary_x509_crt_bundle_end");
+
+
+typedef struct crt_bundle_t {
+    const uint8_t **crts;
+    uint16_t num_certs;
+    size_t x509_crt_bundle_len;
+} crt_bundle_t;
+
+static crt_bundle_t s_crt_bundle;
+
+static int esp_crt_check_signature(mbedtls_x509_crt *child, const uint8_t *pub_key_buf, size_t pub_key_len);
+
+
+static int esp_crt_check_signature(mbedtls_x509_crt *child, const uint8_t *pub_key_buf, size_t pub_key_len)
+{
+    int ret = 0;
+    mbedtls_x509_crt parent;
+    const mbedtls_md_info_t *md_info;
+    unsigned char hash[MBEDTLS_MD_MAX_SIZE];
+
+    mbedtls_x509_crt_init(&parent);
+
+    if ( (ret = mbedtls_pk_parse_public_key(&parent.pk, pub_key_buf, pub_key_len) ) != 0) {
+        ESP_LOGE(TAG, "PK parse failed with error %X", ret);
+        goto cleanup;
+    }
+
+
+    // Fast check to avoid expensive computations when not necessary
+    if (!mbedtls_pk_can_do(&parent.pk, child->sig_pk)) {
+        ESP_LOGE(TAG, "Simple compare failed");
+        ret = -1;
+        goto cleanup;
+    }
+
+    md_info = mbedtls_md_info_from_type(child->sig_md);
+    if ( (ret = mbedtls_md( md_info, child->tbs.p, child->tbs.len, hash )) != 0 ) {
+        ESP_LOGE(TAG, "Internal mbedTLS error %X", ret);
+        goto cleanup;
+    }
+
+    if ( (ret = mbedtls_pk_verify_ext( child->sig_pk, child->sig_opts, &parent.pk,
+                                       child->sig_md, hash, mbedtls_md_get_size( md_info ),
+                                       child->sig.p, child->sig.len )) != 0 ) {
+
+        ESP_LOGE(TAG, "PK verify failed with error %X", ret);
+        goto cleanup;
+    }
+cleanup:
+    mbedtls_x509_crt_free(&parent);
+
+    return ret;
+}
+
+
+/* This callback is called for every certificate in the chain. If the chain
+ * is proper each intermediate certificate is validated through its parent
+ * in the x509_crt_verify_chain() function. So this callback should
+ * only verify the first untrusted link in the chain is signed by the
+ * root certificate in the trusted bundle
+*/
+int esp_crt_verify_callback(void *buf, mbedtls_x509_crt *crt, int depth, uint32_t *flags)
+{
+    mbedtls_x509_crt *child = crt;
+
+    /* It's OK for a trusted cert to have a weak signature hash alg.
+       as we already trust this certificate */
+    uint32_t flags_filtered = *flags & ~(MBEDTLS_X509_BADCERT_BAD_MD);
+
+    if (flags_filtered != MBEDTLS_X509_BADCERT_NOT_TRUSTED) {
+        return 0;
+    }
+
+
+    if (s_crt_bundle.crts == NULL) {
+        ESP_LOGE(TAG, "No certificates in bundle");
+        return MBEDTLS_ERR_X509_FATAL_ERROR;
+    }
+
+    ESP_LOGD(TAG, "%d certificates in bundle", s_crt_bundle.num_certs);
+
+    size_t name_len = 0;
+    const uint8_t *crt_name;
+
+    bool crt_found = false;
+    int start = 0;
+    int end = s_crt_bundle.num_certs - 1;
+    int middle = (end - start) / 2;
+
+    /* Look for the certificate using binary search on subject name */
+    while (start <= end) {
+        name_len = s_crt_bundle.crts[middle][0] << 8 | s_crt_bundle.crts[middle][1];
+        crt_name = s_crt_bundle.crts[middle] + CRT_HEADER_OFFSET;
+
+        int cmp_res = memcmp(child->issuer_raw.p, crt_name, name_len );
+        if (cmp_res == 0) {
+            crt_found = true;
+            break;
+        } else if (cmp_res < 0) {
+            end = middle - 1;
+        } else {
+            start = middle + 1;
+        }
+        middle = (start + end) / 2;
+    }
+
+    int ret = MBEDTLS_ERR_X509_FATAL_ERROR;
+    if (crt_found) {
+        size_t key_len = s_crt_bundle.crts[middle][2] << 8 | s_crt_bundle.crts[middle][3];
+        ret = esp_crt_check_signature(child, s_crt_bundle.crts[middle] + CRT_HEADER_OFFSET + name_len, key_len);
+    }
+
+    if (ret == 0) {
+        ESP_LOGI(TAG, "Certificate validated");
+        *flags = 0;
+        return 0;
+    }
+
+    ESP_LOGE(TAG, "Failed to verify certificate");
+    return MBEDTLS_ERR_X509_FATAL_ERROR;
+}
+
+
+/* Initialize the bundle into an array so we can do binary search for certs,
+   the bundle generated by the python utility is already presorted by subject name
+ */
+static esp_err_t esp_crt_bundle_init(const uint8_t *x509_bundle, size_t bundle_size)
+{
+    if (bundle_size < BUNDLE_HEADER_OFFSET + CRT_HEADER_OFFSET) {
+        ESP_LOGE(TAG, "Invalid certificate bundle");
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    uint16_t num_certs = (x509_bundle[0] << 8) | x509_bundle[1];
+    if (num_certs > CONFIG_MBEDTLS_CERTIFICATE_BUNDLE_MAX_CERTS) {
+        ESP_LOGE(TAG, "No. of certs in the certificate bundle = %d exceeds\n"
+                      "Max allowed certificates in the certificate bundle = %d\n"
+                      "Please update the menuconfig option with appropriate value", num_certs, CONFIG_MBEDTLS_CERTIFICATE_BUNDLE_MAX_CERTS);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    const uint8_t **crts = calloc(num_certs, sizeof(x509_bundle));
+    if (crts == NULL) {
+        ESP_LOGE(TAG, "Unable to allocate memory for bundle");
+        return ESP_ERR_NO_MEM;
+    }
+
+    const uint8_t *cur_crt;
+    /* This is the maximum region that is allowed to access */
+    const uint8_t *bundle_end = x509_bundle + bundle_size;
+    cur_crt = x509_bundle + BUNDLE_HEADER_OFFSET;
+
+    for (int i = 0; i < num_certs; i++) {
+        crts[i] = cur_crt;
+        if (cur_crt + CRT_HEADER_OFFSET > bundle_end) {
+            ESP_LOGE(TAG, "Invalid certificate bundle");
+            free(crts);
+            return ESP_ERR_INVALID_ARG;
+        }
+        size_t name_len = cur_crt[0] << 8 | cur_crt[1];
+        size_t key_len = cur_crt[2] << 8 | cur_crt[3];
+        cur_crt = cur_crt + CRT_HEADER_OFFSET + name_len + key_len;
+    }
+
+    if (cur_crt > bundle_end) {
+        ESP_LOGE(TAG, "Invalid certificate bundle");
+        free(crts);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    /* The previous crt bundle is only updated when initialization of the
+     * current crt_bundle is successful */
+    /* Free previous crt_bundle */
+    free(s_crt_bundle.crts);
+    s_crt_bundle.num_certs = num_certs;
+    s_crt_bundle.crts = crts;
+    return ESP_OK;
+}
+
+esp_err_t esp_crt_bundle_attach(void *conf)
+{
+    esp_err_t ret = ESP_OK;
+    // If no bundle has been set by the user then use the bundle embedded in the binary
+    if (s_crt_bundle.crts == NULL) {
+        ret = esp_crt_bundle_init(x509_crt_imported_bundle_bin_start, x509_crt_imported_bundle_bin_end - x509_crt_imported_bundle_bin_start);
+    }
+
+    if (ret != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to attach bundle");
+        return ret;
+    }
+
+    if (conf) {
+        /* point to a dummy certificate
+         * This is only required so that the
+         * cacert_ptr passes non-NULL check during handshake
+         */
+        mbedtls_ssl_config *ssl_conf = (mbedtls_ssl_config *)conf;
+        mbedtls_x509_crt_init(&s_dummy_crt);
+        mbedtls_ssl_conf_ca_chain(ssl_conf, &s_dummy_crt, NULL);
+        mbedtls_ssl_conf_verify(ssl_conf, esp_crt_verify_callback, NULL);
+    }
+
+    return ret;
+}
+
+void esp_crt_bundle_detach(mbedtls_ssl_config *conf)
+{
+    free(s_crt_bundle.crts);
+    s_crt_bundle.crts = NULL;
+    if (conf) {
+        mbedtls_ssl_conf_verify(conf, NULL, NULL);
+    }
+}
+
+esp_err_t esp_crt_bundle_set(const uint8_t *x509_bundle, size_t bundle_size)
+{
+    return esp_crt_bundle_init(x509_bundle, bundle_size);
+}