From b076101a9a8cd278b3c32fabc5e22db3d0ee3f42 Mon Sep 17 00:00:00 2001
From: nfebe <fenn25.fn@gmail.com>
Date: Thu, 16 Oct 2025 15:34:30 +0200
Subject: [PATCH] fix(sharing): Allow public share access for everyone

When a logged-in user accesses a public share link in the same browser,

the system was incorrectly checking if that user's groups were excluded

from creating link shares. This caused share not found errors for users

in excluded groups, even though public shares should be accessible to anyone

with the link.

The group exclusion setting (`shareapi_allow_links_exclude_groups`) is

intended to restrict share creation, not share access. Public shares

are meant to be anonymous and accessible regardless of the viewer identity

or group membership.

We now check the exclusion for the share creator and not the viewer.

Signed-off-by: nfebe <fenn25.fn@gmail.com>

[skip ci]
---
 lib/private/Share20/Manager.php   | 28 +++++++++++++++++++++++++---
 lib/public/Share/IManager.php     |  4 +++-
 tests/lib/Share20/ManagerTest.php | 10 +++++++++-
 3 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/lib/private/Share20/Manager.php b/lib/private/Share20/Manager.php
index 0998e58e270..c4449936461 100644
--- a/lib/private/Share20/Manager.php
+++ b/lib/private/Share20/Manager.php
@@ -1402,7 +1402,7 @@ class Manager implements IManager {
 		}
 		$share = null;
 		try {
-			if ($this->shareApiAllowLinks()) {
+			if ($this->config->getAppValue('core', 'shareapi_allow_links', 'yes') === 'yes') {
 				$provider = $this->factory->getProviderForType(IShare::TYPE_LINK);
 				$share = $provider->getShareByToken($token);
 			}
@@ -1485,6 +1485,17 @@ class Manager implements IManager {
 				}
 			}
 		}
+
+		// For link and email shares, verify the share owner can still create such shares
+		if ($share->getShareType() === IShare::TYPE_LINK || $share->getShareType() === IShare::TYPE_EMAIL) {
+			$shareOwner = $this->userManager->get($share->getShareOwner());
+			if ($shareOwner === null) {
+				throw new ShareNotFound($this->l->t('The requested share does not exist anymore'));
+			}
+			if (!$this->userCanCreateLinkShares($shareOwner)) {
+				throw new ShareNotFound($this->l->t('The requested share does not exist anymore'));
+			}
+		}
 	}
 
 	/**
@@ -1731,14 +1742,15 @@ class Manager implements IManager {
 	/**
 	 * Is public link sharing enabled
 	 *
+	 * @param ?IUser $user User to check against group exclusions, defaults to current session user
 	 * @return bool
 	 */
-	public function shareApiAllowLinks() {
+	public function shareApiAllowLinks(?IUser $user = null) {
 		if ($this->config->getAppValue('core', 'shareapi_allow_links', 'yes') !== 'yes') {
 			return false;
 		}
 
-		$user = $this->userSession->getUser();
+		$user = $user ?? $this->userSession->getUser();
 		if ($user) {
 			$excludedGroups = json_decode($this->config->getAppValue('core', 'shareapi_allow_links_exclude_groups', '[]'));
 			if ($excludedGroups) {
@@ -1750,6 +1762,16 @@ class Manager implements IManager {
 		return true;
 	}
 
+	/**
+	 * Check if a specific user can create link shares
+	 *
+	 * @param IUser $user The user to check
+	 * @return bool
+	 */
+	protected function userCanCreateLinkShares(IUser $user): bool {
+		return $this->shareApiAllowLinks($user);
+	}
+
 	/**
 	 * Is password on public link requires
 	 *
diff --git a/lib/public/Share/IManager.php b/lib/public/Share/IManager.php
index b07bc8f8051..e934f6112d1 100644
--- a/lib/public/Share/IManager.php
+++ b/lib/public/Share/IManager.php
@@ -294,10 +294,12 @@ interface IManager {
 	/**
 	 * Is public link sharing enabled
 	 *
+	 * @param ?IUser $user User to check against group exclusions, defaults to current session user
 	 * @return bool
 	 * @since 9.0.0
+	 * @since 33.0.0 Added optional $user parameter
 	 */
-	public function shareApiAllowLinks();
+	public function shareApiAllowLinks(?IUser $user = null);
 
 	/**
 	 * Is password on public link required
diff --git a/tests/lib/Share20/ManagerTest.php b/tests/lib/Share20/ManagerTest.php
index 561e7e52bce..dff5e8489ea 100644
--- a/tests/lib/Share20/ManagerTest.php
+++ b/tests/lib/Share20/ManagerTest.php
@@ -3227,21 +3227,29 @@ class ManagerTest extends \Test\TestCase {
 
 	public function testGetShareByTokenPublicUploadDisabled() {
 		$this->config
-			->expects($this->exactly(3))
+			->expects($this->exactly(5))
 			->method('getAppValue')
 			->willReturnMap([
 				['core', 'shareapi_allow_links', 'yes', 'yes'],
 				['core', 'shareapi_allow_public_upload', 'yes', 'no'],
 				['files_sharing', 'hide_disabled_user_shares', 'no', 'no'],
+				['core', 'shareapi_allow_links_exclude_groups', '[]', '[]'],
 			]);
 
 		$share = $this->manager->newShare();
 		$share->setShareType(IShare::TYPE_LINK)
 			->setPermissions(\OCP\Constants::PERMISSION_READ | \OCP\Constants::PERMISSION_CREATE | \OCP\Constants::PERMISSION_UPDATE);
 		$share->setSharedWith('sharedWith');
+		$share->setShareOwner('shareOwner');
 		$folder = $this->createMock(\OC\Files\Node\Folder::class);
 		$share->setNode($folder);
 
+		$shareOwner = $this->createMock(IUser::class);
+		$this->userManager->expects($this->once())
+			->method('get')
+			->with('shareOwner')
+			->willReturn($shareOwner);
+
 		$this->defaultProvider->expects($this->once())
 			->method('getShareByToken')
 			->willReturn('validToken')