We must resolve to the proper usergroup share

lib/private/share20/defaultshareprovider.php

@@ -495,6 +495,9 @@ class DefaultShareProvider implements IShareProvider {
 		} else if ($shareType === \OCP\Share::SHARE_TYPE_GROUP) {
 			$allGroups = $this->groupManager->getUserGroups($user);
 
+			/** @var Share[] $shares2 */
+			$shares2 = [];
+
 			$start = 0;
 			while(true) {
 				$groups = array_slice($allGroups, $start, 100);
@@ -528,7 +531,7 @@ class DefaultShareProvider implements IShareProvider {
 						$offset--;
 						continue;
 					}
-					$shares[] = $this->createShare($data);
+					$shares2[] = $this->createShare($data);
 				}
 				$cursor->closeCursor();
 			}
@@ -537,7 +540,9 @@ class DefaultShareProvider implements IShareProvider {
  			 * Resolve all group shares to user specific shares
  			 * TODO: Optmize this!
  			 */
-			$shares = array_map([$this, 'resolveGroupShare'], $shares);
+			foreach($shares2 as $share) {
+				$shares[] = $this->resolveGroupShare($share, $user);
+			}
 		} else {
 			throw new BackendError('Invalid backend');
 		}
@@ -674,15 +679,18 @@ class DefaultShareProvider implements IShareProvider {
 	 * Thus if the user moved their group share make sure this is properly reflected here.
 	 *
 	 * @param Share $share
+	 * @param IUser $user
 	 * @return Share Returns the updated share if one was found else return the original share.
 	 */
-	private function resolveGroupShare(Share $share) {
+	private function resolveGroupShare(Share $share, IUser $user) {
 		$qb = $this->dbConn->getQueryBuilder();
 
 		$stmt = $qb->select('*')
 			->from('share')
 			->where($qb->expr()->eq('parent', $qb->createNamedParameter($share->getId())))
 			->andWhere($qb->expr()->eq('share_type', $qb->createNamedParameter(self::SHARE_TYPE_USERGROUP)))
+			->andWhere($qb->expr()->eq('share_with', $qb->createNamedParameter($user->getUID())))
+			->setMaxResults(1)
 			->execute();
 
 		$data = $stmt->fetch();

tests/lib/share20/defaultshareprovidertest.php

@@ -881,6 +881,27 @@ class DefaultShareProviderTest extends \Test\TestCase {
 		$this->assertEquals(1, $qb->execute());
 		$id = $qb->getLastInsertId();
 
+		/*
+		 * Wrong share. Should not be taken by code.
+		 */
+		$qb = $this->dbConn->getQueryBuilder();
+		$qb->insert('share')
+			->values([
+				'share_type' => $qb->expr()->literal(2),
+				'share_with' => $qb->expr()->literal('user2'),
+				'uid_owner' => $qb->expr()->literal('shareOwner'),
+				'uid_initiator' => $qb->expr()->literal('sharedBy'),
+				'item_type'   => $qb->expr()->literal('file'),
+				'file_source' => $qb->expr()->literal(42),
+				'file_target' => $qb->expr()->literal('wrongTarget'),
+				'permissions' => $qb->expr()->literal(31),
+				'parent' => $qb->expr()->literal($id),
+			]);
+		$this->assertEquals(1, $qb->execute());
+
+		/*
+		 * Correct share. should be taken by code path.
+		 */
 		$qb = $this->dbConn->getQueryBuilder();
 		$qb->insert('share')
 			->values([