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 <[email protected]>

lib/private/Share20/Manager.php

@@ -1413,7 +1413,7 @@ public function getShareByToken($token) {
 		}
 		$share = null;
 		try {
-			if ($this->shareApiAllowLinks()) {
+			if ($this->config->getAppValue('core', 'shareapi_allow_links', 'yes') === 'yes') {
 				$provider = $this->factory->getProviderForType(IShare::TYPE_LINK);
 				$share = $provider->getShareByToken($token);
 			}
@@ -1496,6 +1496,17 @@ protected function checkShare(IShare $share): void {
 				}
 			}
 		}
+
+		// For link and email shares, verify the share owner can still create such shares
+		if ($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'));
+			}
+		}
 	}
 
 	/**
@@ -1742,14 +1753,15 @@ public function shareApiEnabled() {
 	/**
 	 * 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) {
@@ -1761,6 +1773,16 @@ public function shareApiAllowLinks() {
 		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
 	 *

lib/public/Share/IManager.php

@@ -298,10 +298,12 @@ public function shareApiEnabled();
 	/**
 	 * 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 31.0.12 Added optional $user parameter
 	 */
-	public function shareApiAllowLinks();
+	public function shareApiAllowLinks(?IUser $user = null);
 
 	/**
 	 * Is password on public link required

tests/lib/Share20/ManagerTest.php

@@ -3260,21 +3260,29 @@ public function testGetShareByTokenWithPublicLinksDisabled(): void {
 
 	public function testGetShareByTokenPublicUploadDisabled(): void {
 		$this->config
-			->expects($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')
@@ -3285,6 +3293,87 @@ public function testGetShareByTokenPublicUploadDisabled(): void {
 		$this->assertSame(\OCP\Constants::PERMISSION_READ, $res->getPermissions());
 	}
 
+	public function testGetShareByTokenShareOwnerExcludedFromLinkShares(): void {
+		$this->expectException(ShareNotFound::class);
+		$this->expectExceptionMessage('The requested share does not exist anymore');
+
+		$this->config
+			->expects($this->exactly(4))
+			->method('getAppValue')
+			->willReturnMap([
+				['core', 'shareapi_allow_links', 'yes', 'yes'],
+				['files_sharing', 'hide_disabled_user_shares', 'no', 'no'],
+				['core', 'shareapi_allow_links_exclude_groups', '[]', '["excludedGroup"]'],
+			]);
+
+		$this->l->expects($this->once())
+			->method('t')
+			->willReturnArgument(0);
+
+		$share = $this->manager->newShare();
+		$share->setShareType(IShare::TYPE_LINK)
+			->setPermissions(Constants::PERMISSION_READ);
+		$share->setShareOwner('shareOwner');
+		$file = $this->createMock(File::class);
+		$share->setNode($file);
+
+		$shareOwner = $this->createMock(IUser::class);
+		$this->userManager->expects($this->once())
+			->method('get')
+			->with('shareOwner')
+			->willReturn($shareOwner);
+
+		$this->groupManager->expects($this->once())
+			->method('getUserGroupIds')
+			->with($shareOwner)
+			->willReturn(['excludedGroup', 'otherGroup']);
+
+		$this->defaultProvider->expects($this->once())
+			->method('getShareByToken')
+			->with('token')
+			->willReturn($share);
+
+		$this->manager->getShareByToken('token');
+	}
+
+	public function testGetShareByTokenShareOwnerNotExcludedFromLinkShares(): void {
+		$this->config
+			->expects($this->exactly(4))
+			->method('getAppValue')
+			->willReturnMap([
+				['core', 'shareapi_allow_links', 'yes', 'yes'],
+				['files_sharing', 'hide_disabled_user_shares', 'no', 'no'],
+				['core', 'shareapi_allow_links_exclude_groups', '[]', '["excludedGroup"]'],
+			]);
+
+		$share = $this->manager->newShare();
+		$share->setShareType(IShare::TYPE_LINK)
+			->setPermissions(Constants::PERMISSION_READ);
+		$share->setShareOwner('shareOwner');
+		$file = $this->createMock(File::class);
+		$share->setNode($file);
+
+		$shareOwner = $this->createMock(IUser::class);
+		$this->userManager->expects($this->once())
+			->method('get')
+			->with('shareOwner')
+			->willReturn($shareOwner);
+
+		$this->groupManager->expects($this->once())
+			->method('getUserGroupIds')
+			->with($shareOwner)
+			->willReturn(['allowedGroup', 'otherGroup']);
+
+		$this->defaultProvider->expects($this->once())
+			->method('getShareByToken')
+			->with('token')
+			->willReturn($share);
+
+		$res = $this->manager->getShareByToken('token');
+
+		$this->assertSame($share, $res);
+	}
+
 	public function testCheckPasswordNoLinkShare(): void {
 		$share = $this->createMock(IShare::class);
 		$share->method('getShareType')->willReturn(IShare::TYPE_USER);