TYPO3 Core

This issue does not seem be exist in TYPO3 6.2.

Where is the warning raised?

This issue also exists in 6.2 incl. 6.2.4.

The warning is raised if you have e.g. set open_basedir restrictions, the RTE.default.contentCSS and enter the QuickEdit mode in the Page module.

PHP Warning
PHP Warning: file_exists(): open_basedir restriction in effect. 
File(/var/typo3conf/ext/xxx/Resources/Public/StyleSheet/Rte.css) 
is not within the allowed path(s): (/var/www/xxxxx/web:/var/www/xxxxx/tmp:/usr/share/php5:/tmp) in 
/var/www/xxxxx/web/TYPO3.CMS/typo3/sysext/rtehtmlarea/Classes/RteHtmlAreaBase.php line 534

In RteHtmlAreaBase::getContentCssFileName the absolute path to the css file is miscalculated if QuickEdit mode is choosen.

Maybe changing

if ($fileName) {
    $fileName = $this->getFullFileName($fileName);
}
$absolutePath = $fileName ? GeneralUtility::resolveBackPath(PATH_site . ($this->is_FE() || $this->isFrontendEditActive() ? '' : TYPO3_mainDir) . $fileName) : '';

to

$absolutePath = $fileName ? GeneralUtility::getFileAbsFileName($fileName) : '';        
if ($fileName) {
    $fileName = $this->getFullFileName($fileName);
}

will solve this.

Patch set 1 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33569

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33568

Patch set 2 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33569

Patch set 3 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33569

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33568

Patch set 4 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33569

Patch set 2 for branch TYPO3_6-2 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at http://review.typo3.org/33823