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FSMoVe

FSMoVe (File System Model Verifier) is a practical and effective approach for identifying faults involving ordering violations missing notifiers in Puppet programs. To do so, it records the system call trace produced by the execution of a Puppet manifest through strace. Then, it operates as follows. First, FSMoVe models the system call trace of a Puppet execution in a representation that allows us to precisely capture the interactions of higher-level programming constructs (i.e., Puppet resources) with the file system. By examining their interplays, FSMoVe infers the set of the expected relationships of every Puppet resource with each other. These relationships correspond to either notifications (e.g., resource x should notify resource y) or ordering constraints(e.g., x should run before y). Then, for the given Puppet program, FSMoVe statically builds a dependency graph that reflects all the ordering relationships and notifications that have been specified in Puppet manifests by the developer. Finally, it verifies whether the expected relationships (as inferred from the analysis of traces) hold with respect to the dependency graph.

Building

Build Docker Images

This repository comes with a Docker image that contains an environment for executing and analyzing Puppet programs using FSMoVe. To build the Docker image locally, run

docker build -t fsmove --build-arg IMAGE_NAME=<base-image> .

where <base-image> is the base Docker used to set up the environment. For example, to build the Docker image on top of Debian Buster, run

docker build -t fsmove --build-arg IMAGE_NAME=debian:buster .

Building from source

To build FSMoVe from source, you have to install some necessary packages first

apt install opam m4

Then, install OCaml compiler (version 5.1.0) by running

opam init -y
eval `opam config env`
opam switch 5.1.0

Next, install some required opam packages used by FSMoVe

eval `opam config env`
opam install -y ppx_jane core core_unix camlp-streams yojson dune ounit fd-send-recv fpath

Finally, build FSMoVe by running

dune build -p fsmove
dune install

Running Tests

To run unit tests, run the following command

dune runtest

This will produce something that is similar to the following

run_tests alias test/runtest
................................................................
Ran: 64 tests in: 0.11 seconds.
OK

Usage

> fsmove -help
Applies a Puppet manifest and collects its system call trace.

  fsmove

=== flags ===

  -catalog Path            to the compiled catalog of Puppet manifest.
  -mode Analysis           mode; either online or offline
  [-dump-puppet-out File]  to store output from Puppet execution (for debugging
                           only)
  [-graph-file File]       to store the dependency graph inferred by the
                           compiled catalog.
  [-graph-format Format]   for storing the dependency graph of the provided
                           Puppet manifest.
  [-manifest Path]         to the entrypoint manifest that we need to apply.
                           (Avaiable only when mode is 'online')
  [-modulepath Path]       to the directory of the Puppet modules. (Available
                           only when mode is 'online')
  [-package-notify]        Consider missing notifiers from packages to services
  [-print-stats]           Print stats about execution and analysis
  [-trace-file Path]       to the trace file produced by the 'strace' tool.
  [-build-info]            print info about this build and exit
  [-version]               print the version of this build and exit
  [-help]                  print this help text and exit
                           (alias: -?)

Run and analyze a real-world Puppet module

To run and analyze a real-world Puppet module through FSMoVe, we will use the Docker image built in a previous step (i.e., fsmove) in order to spawn a fresh environment for Puppet. Our image expects the following arguments:

  • -m: The name of Puppet module as it is specified in Forge API.
  • -i: The version of the module to analyze or latest to examine the latest version.
  • -s: A command-line flag used to monitor Puppet execution with the strace system call tracing utility.

For example, to run and analyze the alertlogic-al_agents module

docker run --rm -ti \
  --security-opt seccomp:unconfined \
  -v <output-dir>:/home/fsmove/data fsmove \
  -m alertlogic-al_agents -i 0.2.0 -s

A few explanations:

The option --security-opt seccomp:unconfined is used to enable system call tracing inside the Docker container. The -v option is used to mount a local volume insider Docker container. This is used to store all files generated by the execution and analysis of the Puppet module into the provided directory <output-dir>. Specifically, FSMoVe produces the following six (6) files inside the <output-dir> directory:

  • alertlogic-al_agents.json: the compiled catalog of the corresponding Puppet module.
  • alertlogic-al_agents.strace: a system call trace produced by strace.
  • alertlogic-al_agents.size: the size of system call trace (in bytes)
  • application.time: time spent to apply the module.
  • alertlogic-al_agents.times: time spent on trace analysis and fault detection
  • output: faults detected by FSMoVe.

The contents of the output file are similar to

Missing Ordering Relationships:
===============================
Number of MOR: 1
Pairs:
  * Exec[download]: /etc/puppet/code/environments/production/modules/al_agents/manifests/install.pp: 7
  * Package[al-agent]: /etc/puppet/code/environments/production/modules/al_agents/manifests/install.pp: 24 =>
      Conflict on 1 resources:
      - /tmp/al-agent: Produced by Exec[download] ( open at line 54333 ) and Consumed by Package[al-agent] ( open at line 62579 )

Analysis time: 0.292564153671

In particular, FSMoVe detects one missing ordering relationship (MOR) between the Puppet resource Exec[download] (defined in the install.pp file, line 7), and the resource Package[al-agent] (defined in the install.pp file, line 24). These resources are conflicting on one file, but there is no dependency between them. Specifically, Exec[download] produces the file /tmp/al-agent, while Package[al-agent] consumes the same file. For debugging purposes, FSMoVe also reports the system call and the corresponding line in the resulting alertlogin-al_agent.strace file. For example, ( open at line 54333 ) indicates that Exec[download] produced /tmp/al-agent by calling the open() system call as it appears at line 54333 of the corresponding strace file.

Publications

The tool is described in detail in the following paper.

The research artifact associated with this tool can be found at https://github.com/theosotr/fsmove-eval.