从 docker 容器中打开 DGRAM 套接字失败（权限被拒绝）

Question

我是运行一个应用程序，它构建 ICMP ECHO 请求并将其发送到几个不同的 IP 地址。该应用程序是在 Crystal 中编写的。尝试从 crystal docker 容器中打开套接字时，Crystal 引发异常：权限被拒绝。

在容器中，我没有问题运行 ping 8.8.8.8。

运行 macos上的应用，我没问题。

阅读有关 apparmor 和 seccomp 的 https://docs.docker.com/engine/security/apparmor/ and https://docs.docker.com/engine/security/seccomp/ 页面，我确定我找到了解决方案，但问题仍未解决，即使运行为 docker run --rm --security-opt seccomp=unconfined --security-opt apparmor=unconfined socket_permission

update/edit：深入了解 capabilities(7) 后，我将以下行添加到我的 docker 文件中：RUN setcap cap_net_raw+ep bin/ping trying让套接字打开但不改变。

谢谢！

相关 crystal 套接字代码，完整的工作代码示例如下：

  # send request
  address = Socket::IPAddress.new host, 0
  socket = IPSocket.new Socket::Family::INET, Socket::Type::DGRAM, Socket::Protocol::ICMP
  socket.send slice, to: address

Docker 文件：

FROM crystallang/crystal:0.23.1
WORKDIR /opt
COPY src/ping.cr src/
RUN mkdir bin

RUN crystal -v
RUN crystal build -o bin/ping src/ping.cr

ENTRYPOINT ["/bin/sh","-c"]
CMD ["/opt/bin/ping"]

运行代码，首先是本地代码，然后是 docker:

#!/bin/bash
crystal run src/ping.cr
docker build -t socket_permission .
docker run --rm --security-opt seccomp=unconfined --security-opt apparmor=unconfined socket_permission

最后，一个 50 行的 crystal 脚本无法打开 docker 中的套接字：

require "socket"

TYPE = 8_u16
IP_HEADER_SIZE_8 = 20
PACKET_LENGTH_8 = 16
PACKET_LENGTH_16 = 8
MESSAGE = " ICMP"

def ping
  sequence = 0_u16
  sender_id = 0_u16
  host = "8.8.8.8"

  # initialize packet with MESSAGE
  packet = Array(UInt16).new PACKET_LENGTH_16 do |i|
    MESSAGE[ i % MESSAGE.size ].ord.to_u16
  end

  # build out ICMP header
  packet[0] = (TYPE.to_u16 << 8)
  packet[1] = 0_u16
  packet[2] = sender_id
  packet[3] = sequence

  # calculate checksum
  checksum = 0_u32
  packet.each do |byte|
    checksum += byte
  end
  checksum += checksum >> 16
  checksum = checksum ^ 0xffff_ffff_u32
  packet[1] = checksum.to_u16

  # convert packet to 8 bit words
  slice = Bytes.new(PACKET_LENGTH_8)

  eight_bit_packet = packet.map do |word|
    [(word >> 8), (word & 0xff)]
  end.flatten.map(&.to_u8)

  eight_bit_packet.each_with_index do |chr, i|
    slice[i] = chr
  end

  # send request
  address = Socket::IPAddress.new host, 0
  socket = IPSocket.new Socket::Family::INET, Socket::Type::DGRAM, Socket::Protocol::ICMP
  socket.send slice, to: address

  # receive response
  buffer = Bytes.new(PACKET_LENGTH_8 + IP_HEADER_SIZE_8)
  count, address = socket.receive buffer
  length = buffer.size
  icmp_data = buffer[IP_HEADER_SIZE_8, length-IP_HEADER_SIZE_8]
end

ping

Answer 1

事实证明，答案是 Linux（并扩展为 docker）没有提供与 macOS 对 DGRAM 套接字相同的权限。将套接字声明更改为 socket = IPSocket.new Socket::Family::INET, Socket::Type::RAW, Socket::Protocol::ICMP 允许套接字在 docker.

下连接

运行非 root 上下文中的程序还需要一点。因为原始套接字仅限于 root，二进制文件也必须发布正确的 capability for access to a raw socket, CAP_NET_RAW. However, in docker, this isn't necessary. I was able to get the program to run outside of super-user context by running sudo setcap cap_net_raw+ep bin/ping. This is a decent primer on capabilities and the setpcap command

MacOS 不使用相同的权限系统，因此 setcap 只是一个无法识别的命令。因此，为了在没有超级用户上下文的情况下使上述代码在 macOS 上成功编译和运行，我将套接字创建代码更改为：

socket_type = Socket::Type::RAW

{% if flag?(:darwin) %}
  socket_type = Socket::Type::DGRAM
{% end %}

socket = IPSocket.new Socket::Family::INET, socket_type, Socket::Protocol::ICMP

如果需要，在构建过程的其他地方应用 CAP_NET_RAW 功能以在 linux 中使用。

通过这些更改，我没有看到任何需要更改 Docker 随附的默认设置的 seccomp 或 apparmor 才能运行程序。

从 docker 容器中打开 DGRAM 套接字失败（权限被拒绝）

Opening a DGRAM socket from within a docker container fails (permission denied)

sockets

docker

tcp

crystal-lang

seccomp