AWS mkdir(): Permission denied - php

Question

I am working on AWS ec2 ubuntu machine. My code is in cakephp. When I try to upload any image with crating new folder, I got following warnings.
Warning (2): mkdir(): Permission denied
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 1784]
Warning (2): chmod() [function.chmod]: No such file or directory
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 1785]
Warning (2):
finfo::file(/var/www/html/app/webroot/files/user/image/35/)
[finfo.file]: failed to open stream: No such file or directory
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 1955]
Warning (2): mkdir() [function.mkdir]: Permission denied
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 1784]
Warning (2): chmod() [function.chmod]: No such file or directory
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 1785]
Warning (2):
move_uploaded_file(/var/www/html/app/webroot/files/user/image/35/1439985339.jpg)
[function.move-uploaded-file]: failed to open stream: No such file or
directory [APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line
349]
Warning (2): move_uploaded_file() [function.move-uploaded-file]:
Unable to move '/tmp/phpqvcdzp' to
'/var/www/html/app/webroot/files/user/image/35/1439985339.jpg'
[APP/Plugin/Upload/Model/Behavior/UploadBehavior.php, line 349]
and code is
protected function _mkPath(Model $model, $field, $destDir) {
if (!file_exists($destDir)) {
mkdir($destDir, $this->settings[$model->alias][$field]['mode'], true);
chmod($destDir, $this->settings[$model->alias][$field]['mode']);
}
return true;
}
following is the plugin I am using
http://github.com/josegonzalez/cakephp-upload
should I need to give 777 permission to webroot