Correctly check share permissions when updating a re-sub-share

Before this change the node you shared was checked for permissions.
This works when you reshare the folder that was shared with you.
However when you reshared a subfolder (e.g. as public link),
you could afterwards update the permissions and grant
create+update permissions although the share you receive was read-only.

Signed-off-by: Joas Schilling <coding@schilljs.com>

apps/files_sharing/lib/Controller/ShareAPIController.php

@@ -975,10 +975,20 @@ class ShareAPIController extends OCSController {
 		}
 
 		if ($permissions !== null && $share->getShareOwner() !== $this->currentUser) {
+
+			// Get the root mount point for the user and check the share permissions there
+			$userFolder = $this->rootFolder->getUserFolder($this->currentUser);
+			$userNodes = $userFolder->getById($share->getNodeId());
+			$userNode = array_shift($userNodes);
+
+			$userMountPointId = $userNode->getMountPoint()->getStorageRootId();
+			$userMountPoints = $userFolder->getById($userMountPointId);
+			$userMountPoint = array_shift($userMountPoints);
+
 			/* Check if this is an incoming share */
-			$incomingShares = $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_USER, $share->getNode(), -1, 0);
-			$incomingShares = array_merge($incomingShares, $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_GROUP, $share->getNode(), -1, 0));
-			$incomingShares = array_merge($incomingShares, $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_ROOM, $share->getNode(), -1, 0));
+			$incomingShares = $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_USER, $userMountPoint, -1, 0);
+			$incomingShares = array_merge($incomingShares, $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_GROUP, $userMountPoint, -1, 0));
+			$incomingShares = array_merge($incomingShares, $this->shareManager->getSharedWith($this->currentUser, Share::SHARE_TYPE_ROOM, $userMountPoint, -1, 0));
 
 			/** @var \OCP\Share\IShare[] $incomingShares */
 			if (!empty($incomingShares)) {