more secure combine function

rangitaki-sync.c

@@ -1,60 +1,66 @@
-/* Rangitaki Sync Library
+/*
+ * Rangitaki Sync Library
  *
- * A program for downloading and uploading blog posts,
- * blogs file and media files from a rangitaki blog.
+ * A program for downloading and uploading files over ssh.
+ * Written for the Rangitaki blogging engine.
  *
  * Proudly written in C and with use of libssh (libssh.org)
  *
  * Version: 0.1
  *
- * Authors:
+ * COPYRIGHT (c) 2015 - 2016 The Rangitaki Project
+ * COPYRIGHT (c) 2015 - 2016 Marcel Kapfer (mmk2410)
+ *                           <marcelmichaelkapfer@yahoo.co.nz>
  *
- * COPYRIGHT (c) 2015 The Rangitaki Project
- * COPYRIGHT (c) 2015 Marcel Kapfer (mmk2410) <marcelmichaelkapfer@yahoo.co.nz>
- *
- * License: MIT License
- *
- * Permission is hereby granted, free of charge, to any person obtaining
- * a copy of this software and associated documentation files (the
- * "Software"), to deal in the Software without restriction, including
- * without limitation the rights to use, copy, modify, merge, publish,
- * distribute, sublicense, and/or sell copies of the Software, and to
- * permit persons to whom the Software is furnished to do so, subject to
- * the following conditions:
- *
- * The above copyright notice and this permission notice shall be
- * included in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
- * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
- * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
- * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
- * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
- * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ * MIT License
  *
  */
 
 #include <libssh/libssh.h>
-#include "rangitaki-sync.h"
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/stat.h>
 #include <errno.h>
 #include <string.h>
+#include <assert.h>
 
+#include "rangitaki-sync.h"
 #include "dbg.h"
 
-char * combine(const char * begin, char * end){
-    char * result = malloc(strlen(begin) + strlen(end) + 1);
-    strcpy(result, begin);
-    strcat(result, end);
+#define MAX_FILE_LENGTH 255
+
+char * combine(char *begin, char *end){
+    char *result;
+
+    check(begin != NULL, "Begin can't be NULL.");
+    check(end != NULL, "End can't be NULL.");
+
+    size_t begin_length = strnlen(begin, MAX_FILE_LENGTH - 1);
+    size_t end_length = strnlen(end, MAX_FILE_LENGTH - 1);
+
+    assert(begin_length < MAX_FILE_LENGTH && "Got the begin too long.");
+    assert(end_length < MAX_FILE_LENGTH && "Got the end to long.");
+
+    result = malloc(begin_length + end_length + 1);
+    check(result != NULL, "Failed to define result");
+
+    strncpy(result, begin, MAX_FILE_LENGTH);
+    check(result != NULL, "Failed to copy the string");
+
+    strncat(result, end, MAX_FILE_LENGTH * 2);
+    int rc = strncmp(result, begin, MAX_FILE_LENGTH * 2);
+    check(rc <= 0, "Failed to concat string.");
+
     return result;
+
+error:
+    if (result) free(result);
+    return NULL;
 }
 
 char * getFilename(char *input)
 {
-    check(input != NULL, "Invalid input");
+    check(input != NULL, "Input is NULL.");
     char* string;
 
     string = strdup(input);
@@ -263,7 +269,7 @@ int scp_download(ssh_session ssh, ssh_scp scp, ssh_data *data)
     int rv;
     int size, mode;
     char buffer[16384];
-    const char *local_dir = strdup(data->local_dir);
+    char *local_dir = strdup(data->local_dir);
 
     do {
         rc = ssh_scp_pull_request(scp);