Allow setting SSL cipher list also with MbedTLS

Signed-off-by: DL6ER <dl6er@dl6er.de>

src/civetweb.c

@@ -16805,7 +16805,8 @@ mg_sslctx_init(struct mg_context *phys_ctx, struct mg_domain_context *dom_ctx)
 		return 0;
 	}
 
-	return mbed_sslctx_init(dom_ctx->ssl_ctx, dom_ctx->config[SSL_CERTIFICATE])
+	return mbed_sslctx_init(dom_ctx->ssl_ctx, dom_ctx->config[SSL_CERTIFICATE],
+	                        dom_ctx->config[SSL_CIPHER_LIST])
 	               == 0
 	           ? 1
 	           : 0;

src/mod_mbedtls.inl

@@ -33,7 +33,7 @@ typedef struct {
 
 
 /* public api */
-int mbed_sslctx_init(SSL_CTX *ctx, const char *crt);
+int mbed_sslctx_init(SSL_CTX *ctx, const char *crt, const char *cipherlist);
 void mbed_sslctx_uninit(SSL_CTX *ctx);
 void mbed_ssl_close(mbedtls_ssl_context *ssl);
 int mbed_ssl_accept(mbedtls_ssl_context **ssl,
@@ -43,6 +43,9 @@ int mbed_ssl_accept(mbedtls_ssl_context **ssl,
 int mbed_ssl_read(mbedtls_ssl_context *ssl, unsigned char *buf, int len);
 int mbed_ssl_write(mbedtls_ssl_context *ssl, const unsigned char *buf, int len);
 
+/* Set the ciphersuites to be used by mbedtls using a comma-separated string */
+int mbed_sslctx_set_ciphersuites(mbedtls_ssl_config *conf, const char *cipher_list);
+
 static void mbed_debug(void *context,
                        int level,
                        const char *file,
@@ -52,7 +55,7 @@ static int mbed_ssl_handshake(mbedtls_ssl_context *ssl);
 
 
 int
-mbed_sslctx_init(SSL_CTX *ctx, const char *crt)
+mbed_sslctx_init(SSL_CTX *ctx, const char *crt, const char *cipherlist)
 {
 	mbedtls_ssl_config *conf;
 	int rc;
@@ -154,6 +157,14 @@ mbed_sslctx_init(SSL_CTX *ctx, const char *crt)
 		DEBUG_TRACE("TLS cannot set certificate and private key (%i)", rc);
 		return -1;
 	}
+
+	/* Set ciphersuites if specified */
+	if (cipherlist != NULL &&
+	    cipherlist[0] != '\0' &&
+	    mbed_sslctx_set_ciphersuites(conf, cipherlist) != 0) {
+		DEBUG_TRACE("Failed to set ciphersuites: no valid ciphersuites are found in the list");
+		return -1;
+	}
 	return 0;
 }
 
@@ -279,4 +290,65 @@ mbed_debug(void *user_param,
 	            str);
 }
 
+/**
+ * @brief Sets the list of allowed ciphersuites for an mbedTLS SSL configuration.
+ *
+ * Parses a comma-separated list of ciphersuite names, converts them to their
+ * corresponding mbedTLS ciphersuite IDs, and configures the SSL context to use
+ * only those ciphersuites.
+ *
+ * @param conf Pointer to the mbedTLS SSL configuration structure.
+ * @param cipher_list Comma-separated string of ciphersuite names.
+ * @return 0 on success,
+ *         -1 if conf or cipher_list is NULL,
+ *         -2 if no valid ciphersuites are found in the list.
+ *
+ * @note The ciphersuite ID array is static and must remain valid after the function returns,
+ *       as mbedtls_ssl_conf_ciphersuites() does not copy the array.
+ */
+int mbed_sslctx_set_ciphersuites(mbedtls_ssl_config *conf, const char *cipher_list) {
+	if (conf == NULL || cipher_list == NULL) {
+		return -1;
+	}
+
+	// The array for ciphersuite IDs must remain valid after this function
+	// returns as mbedtls_ssl_conf_ciphersuites() does not copy the array,
+	// but only stores the pointer. We do not allow more than 64 cipher
+	// suites for simplicity.
+	static int ciphersuites[64] = { 0 };
+	size_t count = 0;
+
+	char buf[1024];
+	strncpy(buf, cipher_list, sizeof(buf) - 1);
+	buf[sizeof(buf) - 1] = '\0';
+
+	char *token = strtok(buf, ",");
+	while (token && count < 63) {
+		// Remove leading/trailing whitespace
+		while (*token == ' ' || *token == '\t') token++;
+		char *end = token + strlen(token) - 1;
+		while (end > token && (*end == ' ' || *end == '\t')) {
+			*end = '\0';
+			end--;
+		}
+		const mbedtls_ssl_ciphersuite_t *ciphersuite = mbedtls_ssl_ciphersuite_from_string(token);
+		if (ciphersuite != NULL) {
+			const int id = mbedtls_ssl_ciphersuite_get_id(ciphersuite);
+			DEBUG_TRACE("Adding ciphersuite '%s' (ID %d)", token, id);
+			ciphersuites[count++] = id;
+		}
+		token = strtok(NULL, ",");
+	}
+	ciphersuites[count] = 0;
+
+	if (count == 0) {
+		DEBUG_TRACE("No valid ciphersuites found");
+		return -2; // No valid ciphersuites found
+	}
+
+	// Set the ciphersuites
+	mbedtls_ssl_conf_ciphersuites(conf, ciphersuites);
+	return 0;
+}
+
 #endif /* USE_MBEDTLS */