Library/application launcher for quickly running daemons inside of restricted jails

Clone this repo:
  1. 655c034 Add common /etc paths to --fs-default-paths by Ben Scarlato · 3 weeks ago main release-R127-15917.B stabilize-15926.B
  2. 793a7cc tools: seccomp_policy_lint_unittest: fix baselines by Mike Frysinger · 3 weeks ago
  3. 99e8fd4 minijail-sys: Do not rely on libcap in build script by Sargun Dhillon · 4 weeks ago linux-v2024.05.22
  4. c1df6ba Set embedded_launcher: true for minijail tests by Cole Faust · 3 months ago firmware-R126-15885.B firmware-geralt-15842.B firmware-hps-15892.B release-R125-15853.B release-R126-15886.B stabilize-15855.B stabilize-15857.B stabilize-15888.B stabilize-hps-15890.B
  5. 156ff64 Update link to Sandboxing system services doc by Ben Scarlato · 3 months ago factory-geralt-15840.B

Minijail

The Minijail homepage is https://google.github.io/minijail/.

The main source repo is https://chromium.googlesource.com/chromiumos/platform/minijail.

There might be other copies floating around, but this is the official one!

What is it?

Minijail is a sandboxing and containment tool used in ChromeOS and Android. It provides an executable that can be used to launch and sandbox other programs, and a library that can be used by code to sandbox itself.

Getting the code

You're one git clone away from happiness.

$ git clone https://chromium.googlesource.com/chromiumos/platform/minijail
$ cd minijail

Releases are tagged as linux-vXX: https://chromium.googlesource.com/chromiumos/platform/minijail/+refs

Building

See the HACKING.md document for more details.

Release process

See the RELEASE.md document for more details.

Additional tools

See the tools/README.md document for more details.

Contact

We've got a couple of contact points.

GitHub Pages homepage

The https://google.github.io/minijail/ homepage is maintained in the gh-pages branch, not in the main branch. Changes to it can be sent via Gerrit, but requires a little extra work.

# Make sure you have all the branches, and not only the "main" one.
$ git fetch

# Create a new local branch tracking the remote "gh-pages".
# Git should automatically detect the remote and track it for you.
$ git checkout gh-pages
# If git can't auto-detect the remote, try one of these.
$ git checkout -b gh-pages origin/gh-pages
$ git checkout -b gh-pages cros/gh-pages

# Make your changes like normal, then push them to Gerrit for review.
# Here's a couple of different ways to post changes; you only need one!
$ repo upload -D gh-pages
$ git push origin HEAD:refs/for/gh-pages
$ git push cros HEAD:refs/for/gh-pages

# Now review your changes via Gerrit like normal.

Once a change merges into the gh-pages branch, there is no additional work for you other than waiting -- GitHub periodically syncs with our host, and then it will automatically regenerate the homepage when the gh-pages branch updates.

Talks and presentations

The following talk serves as a good introduction to Minijail and how it can be used.

Video, slides.

Example usage

The ChromiumOS project has a comprehensive sandboxing document that is largely based on Minijail.

After you play with the simple examples below, you should check that out.

Change root to any user

# id
uid=0(root) gid=0(root) groups=0(root),128(pkcs11)
# minijail0 -u jorgelo -g 5000 /usr/bin/id
uid=72178(jorgelo) gid=5000(eng) groups=5000(eng)

Drop root while keeping some capabilities

# minijail0 -u jorgelo -c 3000 -- /bin/cat /proc/self/status
Name: cat
...
CapInh: 0000000000003000
CapPrm: 0000000000003000
CapEff: 0000000000003000
CapBnd: 0000000000003000

Historical notes

Q. “Why is it called minijail0?”

A. It is minijail0 because it was a rewrite of an earlier program named minijail, which was considerably less mini, and in particular had a dependency on libchrome (the ChromeOS packaged version of Chromium's //base). We needed a new name to not collide with the deprecated one.

We didn‘t want to call it minijail2 or something that would make people start using it before we were ready, and it was also concretely less since it dropped libbase, etc. Technically, we needed to be able to fork/preload with minimal extra syscall noise which was too hard with libbase at the time (onexit handlers, etc that called syscalls we didn’t want to allow). Also, Elly made a strong case that C would be the right choice for this for linking and ease of controlled surprise system call use.

https://crrev.com/c/4585/ added the original implementation.

Source: Conversations with original authors, ellyjones@ and wad@.