jafar

README

Jafar

We stepped up the game of simulating censorship upgrading from the evil genius to the evil grand vizier.

Jafar is a censorship simulation tool used for testing OONI. It builds on any system but it really only works on Linux.

Building

We use Go >= 1.16. Jafar also needs the C library headers, iptables installed, and root permissions.

With Linux Alpine edge, you can compile Jafar with:

apk add go git musl-dev iptables
go build -v .

Otherwise, using Docker:

docker build -t jafar-runner .
docker run -it --privileged -v`pwd`:/jafar -w/jafar jafar-runner
go build -v .

Usage

You need to run Jafar as root. You can get a complete list of all flags using ./jafar -help. Jafar is composed of modules. Each module is controllable via flags. We describe modules below.

main

The main module starts all the other modules. If you don't provide the -main-command <command> flag, the code will run until interrupted. If instead you use the -main-command flag, you can specify a command to run inside the censored environment. In such case, the main module will exit when the specified command terminates. Note that the main module will propagate the child exit code, if the child fails.

The command can also include arguments. Make sure you quote the arguments such that your shell passes the whole string to the specified option, as in -main-command 'ls -lha'. This will execute the ls -lha command line inside the censored Jafar context. You can also combine that with quoting and variables interpolation, e.g., -main-command "echo '$USER is the walrus'". The $USER variable will be expanded by your shell. Assuming your user name is paul, then Jafar will lex the main command as echo "paul is the walrus" and will execute it.

Use the -main-user <username> flag to select the user to use for running child commands. By default, we use the nobody user for this purpose. We implement this feature using sudo, therefore you need to make sure that sudo is installed.

iptables

The iptables module is only available on Linux. It exports these flags:

  -iptables-drop-ip value
        Drop traffic to the specified IP address
  -iptables-drop-keyword-hex value
        Drop traffic containing the specified hex keyword
  -iptables-drop-keyword value
        Drop traffic containing the specified keyword
  -iptables-hijack-dns-to string
        Hijack all DNS UDP traffic to the specified endpoint
  -iptables-hijack-https-to string
        Hijack all HTTPS traffic to the specified endpoint
  -iptables-hijack-http-to string
        Hijack all HTTP traffic to the specified endpoint
  -iptables-reset-ip value
        Reset TCP/IP traffic to the specified IP address
  -iptables-reset-keyword-hex value
        Reset TCP/IP traffic containing the specified hex keyword
  -iptables-reset-keyword value
        Reset TCP/IP traffic containing the specified keyword

The difference between drop and reset is that in the former case a packet is dropped, in the latter case a RST is sent.

The difference between ip and keyword flags is that the former match an outgoing IP, the latter uses DPI.

The drop and reset rules allow you to simulate, respectively, when operations timeout and when a connection cannot be established (with reset and ip) or is reset after a keyword is seen (with keyword).

Hijacking DNS traffic is useful, for example, to redirect all DNS UDP traffic from the box to the dns-proxy module.

Hijacking HTTP and HTTPS traffic actually hijacks based on ports rather than on DPI. As a known bug, when hijacking HTTP or HTTPS traffic, we do not hijack traffic owned by root. This is because Jafar runs as root and therefore its traffic must not match the hijack rule.

When matching keywords, the simplest option is to use ASCII strings as in -iptables-drop-keyword ooni. However, you can also specify a sequence of hex bytes, as in -iptables-drop-keyword-hex |6f 6f 6e 69|.

Note that with -iptables-drop-keyword, DNS queries containing such keyword will fail returning EPERM. For a more realistic approach to dropping specific DNS packets, combine DNS traffic hijacking with -dns-proxy-ignore, to "drop" packets at the DNS proxy.

dns-proxy (aka resolver)

The DNS proxy or resolver allows to manipulate DNS. Unless you use DNS hijacking, you will need to configure your application explicitly to use the proxy with application specific command line flags.

  -dns-proxy-address string
        Address where the DNS proxy should listen (default "127.0.0.1:53")
  -dns-proxy-block value
        Register keyword triggering NXDOMAIN censorship
  -dns-proxy-hijack value
        Register keyword triggering redirection to 127.0.0.1
  -dns-proxy-ignore value
        Register keyword causing the proxy to ignore the query

The -dns-proxy-address flag controls the endpoint where the proxy is listening.

The -dns-proxy-block tells the resolver that every incoming request whose query contains the specifed string shall receive an NXDOMAIN reply.

The -dns-proxy-hijack is similar but instead lies and returns to the client that the requested domain is at 127.0.0.1. This is an opportunity to redirect traffic to the HTTP and TLS proxies.

The -dns-proxy-ignore is similar but instead just ignores the query.

http-proxy

The HTTP proxy is an HTTP proxy that may refuse to forward some specific requests. It's controlled by these flags:

  -http-proxy-address string
        Address where the HTTP proxy should listen (default "127.0.0.1:80")
  -http-proxy-block value
        Register keyword triggering HTTP 451 censorship

The -http-proxy-address flag has the same semantics it has for the DNS proxy.

The -http-proxy-block flag tells the proxy that it should return a 451 response for every request whose Host contains the specified string.

tls-proxy

TLS proxy is a proxy that routes traffic to specific servers depending on their SNI value. It is controlled by the following flags:

  -tls-proxy-address string
        Address where the HTTP proxy should listen (default "127.0.0.1:443")
  -tls-proxy-block value
        Register keyword triggering TLS censorship

The -tls-proxy-address flags has the same semantics it has for the DNS proxy.

The -tls-proxy-block specifies which string or strings should cause the proxy to return an internal-erorr alert when the incoming ClientHello's SNI contains one of the strings provided with this option.

bad-proxy

  -bad-proxy-address string
        Address where to listen for TCP connections (default "127.0.0.1:7117")
  -bad-proxy-address-tls string
        Address where to listen for TLS connections (default "127.0.0.1:4114")
  -bad-proxy-tls-output-ca string
        File where to write the CA used by the bad proxy (default "badproxy.pem")

The bad proxy is a proxy that reads some bytes from any incoming connection and then closes the connection without replying anything. This simulates a proxy that is not working properly, hence the name of the module.

When connecting using TLS, the above behaviour happens after the handshake.

We write the CA on the file specified using -bad-proxy-tls-output-ca such that tools like curl(1) can use such CA to avoid TLS handshake errors. The code will generate on the fly a certificate for the provided SNI. Not providing any SNI in the client Hello message will cause the TLS handshake to fail.

uncensored

  -uncensored-resolver-url string
    	URL of an hopefully uncensored resolver (default "dot://1.1.1.1:853")

The HTTP, DNS, and TLS proxies need to resolve domain names. If you setup DNS censorship, they may be affected as well. To avoid this issue, we use a different resolver for them, which by default is dot://1.1.1.1:853. You can change such default by using the -uncensored-resolver-url command line flag. The input URL is <transport>://<domain>[:<port>][/<path>]. Here are some examples:

• system:/// uses the system resolver (i.e. getaddrinfo)
• udp://8.8.8.8:53 uses DNS over UDP
• tcp://8.8.8.8:53 used DNS over TCP
• dot://8.8.8.8:853 uses DNS over TLS
• https://dns.google/dns-query uses DNS over HTTPS

So, for example, if you are using Jafar to censor 1.1.1.1:853, then you most likely want to use -uncensored-resolver-url.

Examples

Block play.google.com with RST injection, force DNS traffic to use the our DNS proxy, and force it to censor play.google.com with NXDOMAIN.

# ./jafar -iptables-reset-keyword play.google.com \
          -iptables-hijack-dns-to 127.0.0.1:5353  \
          -dns-proxy-address 127.0.0.1:5353       \
          -dns-proxy-block play.google.com

Force all traffic through the HTTP and TLS proxy and use them to censor play.google.com using HTTP 451 and responding with TLS alerts:

# ./jafar -iptables-hijack-dns-to 127.0.0.1:5353 \
          -dns-proxy-address 127.0.0.1:5353      \
          -dns-proxy-hijack play.google.com      \
          -http-proxy-block play.google.com      \
          -tls-proxy-block play.google.com

Run ping in a censored environment:

# ./jafar -iptables-drop-ip 8.8.8.8 -main-command 'ping -c3 8.8.8.8'

Run curl in a censored environment where it cannot connect to play.google.com using https:

# ./jafar -iptables-hijack-https-to 127.0.0.1:443         \
          -tls-proxy-block play.google.com                \
          -main-command 'curl -Lv http://play.google.com'

For more usage examples, see ../../testjafar.bash.

Documentation

Overview

Jafar is a censorship simulation tool used for testing OONI.