Buffer overflow in fread and strncpy in C++

I'm getting buffer overflow case from the appscan for the below set of code. I'm not sure what is wrong in it. If someone suggest a solution that would be great. Common Code is for all the platform.

int main()
{
   char* src = NULL;
   char* chenv = getenv("HOME");
   if (chenv == NULL || strlen(chenv) == 0)
       return -1;
   else
   {
       int len = strlen(chenv);
       src = new char[len+1];
       strncpy(src, chenv, len); // AppScan throws buffer overflow
       src[len+1]='\0';
   }
   FILE* fp;
   char content[4096];
   int len = 0;
   fp = fopen("filename.txt", "r");
   if(fp)
   {
       while( (len = fread(content, sizeof(char), sizeof(content), fp))> 0) // AppScan throws buffer overflow on content
       {
           docopy(content, len);// External funtion call. 
       }
   }

   return 0;  
}