沙箱权限

flatpak的一个主要目标就是通过应用间的隔离来提高桌面系统的安全性。这通过使用沙箱来实现，默认地，应用运行的环境对主机的访问很有限。这包括：

• No access to any host files except the runtime, the app, ~/.var/app/$FLATPAK_ID, and $XDG_RUNTIME_DIR/app/$FLATPAK_ID. Only the latter two being writable.

• 无法访问网络。

• 无法访问任何设备节点的（除了 /dev/null ，等等）。（译者注：可能有访问所有null设备的权限）

• 无法访问沙箱之外进程

• 有限的系统调用。举个例子，应用无法使用非标准的网络socket或者ptrace其他进程。

• 有限地访问D-Bus实例的session——一个应用在总线上只能拥有它自己的名字。

• 无法访问主机服务，像X11，system D-Bus或PulseAudio这些。

大部分应用需要访问这些资源。这些主要是在finishing构建步骤完成的，通过清单文件（查看 清单）的 finish-args 部分来配置。

门户（译者注：英文portals）

Portals have already been mentioned in 基本概念. They are a framework for providing access to resources outside of the sandbox, including:

• 用一个本地的文件选择对话框打开文件

• 打开URL

• 打印

• 显示通知

• 截取屏幕

• 禁止用户会话结束、暂停、空转或切换。

• 获取网络状态信息

在许多情况下，门户通过使用系统组件在获取访问某些特定资源的权限之前隐式地向用户获得了许可。举个例子，在打开一个文件的时候，用户用文件选择对话框进行文件选择，可以理解为隐式地授予了应用对选中文件的访问。

这种方式使得应用在需要访问大量数据或服务时避免重复配置， 也让用户可以掌控（译者注：知悉，了解）他们的应用的访问权限。

Interface toolkits like GTK3 and Qt5 implement transparent support for portals, meaning that applications don’t need to do any additional work to use them (it is worth checking which portals each toolkit supports). Applications that aren’t using a toolkit with support for portals can refer to the xdg-desktop-portal API documentation for information on how to use them.

权限手册

虽然应用程序开发人员可以控制他们想要配置的沙箱权限，但是鼓励进行良好的实践。举个例子，Flathub主机托管服务对权限的使用提出了要求，如果使用了某些权限，主机上的软件可能会警告用户。

后面的手册描述了哪些权限可以任意使用，哪些可以根据需要使用，哪些应该避免使用。

标准权限

以下权限提供了应用通常需要访问的基本资源，因此可以自由使用：

• --allow=bluetooth - Allow access to Bluetooth

• --device=dri - OpenGL 渲染

• --device=input - Access to /dev/input

• --share=ipc - share IPC namespace with the host [1]

• --share=network - access the network [2]

• --socket=cups - Talk to the CUPS printing system

• --socket=gpg-agent - Talk to the GPG agent

• --socket=pcsc - Smart card access

• --socket=pulseaudio - Play sound with PulseAudio

• --socket=ssh-auth- Allow access to SSH_AUTH_SOCK

• --socket=wayland - Show windows with Wayland

• --socket=x11 - show windows using X11

• --socket=fallback-x11 - show windows using X11, if Wayland is not available, overrides x11 socket permission. Note that you must still use --socket=wayland for wayland permission

备注

Applications that do not support native Wayland should use --socket=x11 and applications that do should use --socket=fallback-x11 and --socket=wayland. The two configurations here will make it work on both X11 and Wayland sessions of the desktop environment.

D-Bus访问

Access to the entire bus with --socket=system-bus or --socket=session-bus is a security risk and must be avoided, unless the application is a development tool.

flatpak run --log-session-bus <appid> can be used to find the specific D-Bus permissions needed.

Ownership

应用会自动为他们自己命名空间授予访问权限，通常不需要有所有权，尽管如此还是有少量的例外，例如使用 MPRIS来提供媒体控制 。

Talk

Talk permissions can be freely used, although it is recommended to use the minimum required.

文件系统访问

As a general rule, static and permanent filesystem access should be limited as much as possible. This includes:

• 尽量使用门户来代替文件系统访问。

• 尽量使用读取权限来访问，使用 :ro 选项。

• 如果一定要访问home目录，只使用XDG目录访问。

The following permission options are available:

• :ro - read-only access

• :create - read/write access, and create the directory if it doesn’t exist

Additionally the following permissions are available:

host	Access /home, /media, /opt, /run/media and /srv	Includes any subpaths
host-etc	Everything in host and host’s /etc	host’s /etc is mounted at /run/host/etc
host-os	Everything in host and /usr, /bin, /sbin, /lib{32, 64}	/usr is mounted at /run/host/usr
home	Access the home directory	Except ~/.var/app
/some/dir	Access an arbitrary path except any reserved path	Includes any subpaths
~/some/dir	Arbitrary path relative to the home directory	Includes any subpaths
xdg-desktop	Access the XDG desktop directory	$XDG_DESKTOP_DIR or $HOME/Desktop
xdg-documents	Access the XDG documents directory	$XDG_DOCUMENTS_DIR or $HOME/Documents
xdg-download	Access the XDG download directory	$XDG_DOWNLOAD_DIR or $HOME/Downloads
xdg-music	Access the XDG music directory	$XDG_MUSIC_DIR or $HOME/Music
xdg-pictures	Access the XDG pictures directory	$XDG_PICTURES_DIR or $HOME/Pictures
xdg-public-share	Access the XDG public directory	$XDG_PUBLICSHARE_DIR or $HOME/Public
xdg-videos	Access the XDG videos directory	$XDG_VIDEOS_DIR or $HOME/Videos
xdg-templates	Access the XDG templates directory	$XDG_TEMPLATES_DIR or $HOME/Templates
xdg-config	Access the XDG config directory [3]	$XDG_CONFIG_HOME or $HOME/.config
xdg-cache	Access the XDG cache directory [3]	$XDG_CACHE_HOME or $HOME/.cache
xdg-data	Access the XDG data directory [3]	$XDG_DATA_HOME or $HOME/.local/share
xdg-run/path	Access subdirectories of the XDG runtime directory	$XDG_RUNTIME_DIR/path (/run/user/$UID/path)

Except host, host-etc, host-os paths can be added to all the above filesystem options. For example, --filesystem=xdg-documents/path.

Other filesystem access guidelines include:

• --persist=path 选项可以用来将用户目录映射到沙箱的文件系统。这可以避免配置整个home目录访问权限。并且对于在硬编码使用 ~/ 文件路径的应用程序非常有用。

• If an application uses $TMPDIR to contain lock files you may want to add a wrapper script that sets it to $XDG_RUNTIME_DIR/app/$FLATPAK_ID.

• 应该避免与非flatpak安装的应用共享配置。

Reserved Paths

The following paths are reserved for the runtime and Flatpak itself and are never shared:

/app, /bin, /dev, /etc, /lib, /lib32, /lib64, /proc, /run, /run/flatpak, /run/host, /sbin, /usr

Some subpaths of /run are allowed but not the entire directory.

Additionally the following directories from host need to be explicitly requested with --filesystem and are not available with home, host, host-os, host-etc by default:

• ~/.var/app - The app can access only its own directory in ~/.var/app/$FLATPAK_ID

• $XDG_DATA_HOME/flatpak (~/.local/share/flatpak)

• /boot

• /efi

• /root

• /sys

• /tmp

• /var - Note that by default /var/{cache, config, data, tmp} inside the sandbox are the same as ~/.var/app/$FLATPAK_ID/{cache, config, data, cache/tmp}. However an explicit --filesystem=/var will make only /var from host available and those will no longer be available.

• /var/lib/flatpak - /var does not give access to this.

设备访问

尽管不理想， --device=all 可以用来访问控制器和网络摄像头之类的设备。

dconf访问

As of xdg-desktop-portal 1.1.0 and glib 2.60.5 (in the runtime) you do not need direct DConf access in most cases.

As of now this glib version is included in org.freedesktop.Platform//19.08 and org.gnome.Platform//3.34 and newer.

If an application existed prior to these runtimes you can tell Flatpak (>= 1.3.4) to migrate the DConf settings on the host into the sandbox by adding --metadata=X-DConf=migrate-path=/org/example/foo/ to finish-args. The path must be similar to your app-id or it will not be allowed (case is ignored and _ and - are treated equal).

If you are targeting older runtimes or require direct DConf access for other reasons you can use these permissions:

--filesystem=xdg-run/dconf
--filesystem=~/.config/dconf:ro
--talk-name=ca.desrt.dconf
--env=DCONF_USER_CONFIG_DIR=.config/dconf

With those permissions glib will continue using dconf directly.

If you use a newer runtime where dconf is no longer built and still need it you will have to build the dconf GIO module and set --env=GIO_EXTRA_MODULES=/app/lib/gio/modules/.

gvfs access

As of gvfs 1.48, the gvfs daemons and applications use an on-disk socket to communicate, rather than an abstract socket so that the gvfs infrastructure still works when network support is disabled in the application’s sandbox.

A number of different options need to be passed depending on the application’s use of gvfs.

--talk-name=org.gtk.vfs.* is necessary to talk to the gvfs daemons over D-Bus and list mounts using the GIO APIs.

--filesystem=xdg-run/gvfsd is necessary to use the GIO APIs to list and access non-native files using the GIO APIs, using URLs rather than FUSE paths.

--filesystem=xdg-run/gvfs is necessary to give access to the FUSE mounts non-GIO and legacy applications can use. This is what will make native files appear under /run/user/`id -u`/gvfs/.

Typical GNOME and GTK applications should use:

--talk-name=org.gtk.vfs.*
--filesystem=xdg-run/gvfsd

Typical non-GNOME and non-GTK applications should use:

--filesystem=xdg-run/gvfs

No application should be using --talk-name=org.gtk.vfs in its manifest, as there are no D-Bus services named org.gtk.vfs.

External drive access

External drives are mounted by the host system using systemd, udev, udisk fstab etc. and each of them can have different defaults. Flatpak has no control over how and where they get mounted. The following filesystem permissions should work in most cases:

--filesystem=/media
--filesystem=/run/media
--filesystem=/mnt

If --filesystem=host is used /media, /run/media is shared automatically if they exist.

Note that these should not have subpaths in them unless the value of the subpath can be consistently pre-determined. Block device naming depends on the kernel/fstab configuration and cannot be pre-determined.

Footnotes

[1]

This is not necessarily required, but without it the X11 shared memory extension will not work, which is very bad for X11 performance.

[2]

Giving network access also grants access to all host services listening on abstract Unix sockets (due to how network namespaces work), and these have no permission checks. This unfortunately affects e.g. the X server and the session bus which listens to abstract sockets by default. A secure distribution should disable these and just use regular sockets.

[3] (1,2,3)

xdg-{cache, config, data} bind mounts the paths from host to the per-app sandbox directory. Inside the sandbox $XDG_CACHE_HOME, $XDG_CONFIG_HOME and $XDG_DATA_HOME is set to $HOME/.var/app/$FLATPAK_ID/{cache, config, data} respectively. So for example, xdg-data/applications ie. $XDG_DATA_HOME/applications on host is bind mounted to $HOME/.var/app/$FLATPAK_ID/data/applications (inside the sandbox this is $XDG_DATA_HOME/applications). Additionally it’ll have two mount points - one expanded to $XDG_DATA_HOME/applications from the host and another to the sandbox’s $XDG_DATA_HOME/applications ie. $HOME/.var/app/$FLATPAK_ID/data/applications.