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userdoc:gitolite_2fa

2-factor authentication with gitolite.kernel.org

:!: The preferred mechanism for 2-factor authentication is via an SSH key stored on a smartcard device. If you have an account on kernel.org, you qualify for a free nitrokey, so we strongly recommend that instead of setting up TOTP/HOTP you switch to using the Nitrokey for your ssh access instead.

HOTP/TOTP ip-based push validation

Notice: opt-in

CommandSummary
enroll [mode]Enroll with 2-factor authentication (mode=totp or yubikey)
val [token]Validate your current IP address for 24 hours
val-session [token]Validate your current ssh ControlMaster session
val-for-days [days] [token]Validate your current IP address for arbitrary number of days (max=30)
val-subnet [/cidr] [token]Validate a larger subnet for 8 hours
list-val [all]List current validations ("all" includes expired)
inval [ip-address]Invalidate specific IP address (can be "myip", "all" or "all purge")
isvalCheck if your current IP is validated
unenroll [token]Unenroll from 2-factor authentication

Core concepts

Once 2-factor authentication is enabled for a git repository, any write operation from an IP address that hasn't been 2-factor validated will be rejected with a message like the following:

remote: User not enrolled with 2-factor authentication.
remote: FATAL: W VREF/2fa: testing mricon DENIED by VREF/2fa
remote: 2-factor verification failed
remote:
remote: You will need to enroll with 2-factor authentication
remote: before you can push to this repository.
remote:
remote: If you need more help, please see the following link:
remote:     https://korg.wiki.kernel.org/index.php?title=Userdoc:gitolite_2fa
remote:
remote: error: hook declined to update refs/heads/master

To allow the push to succeed, you will need to first validate the IP address with your 2-factor token, which will allow all pushes from that IP address to succeed – until the validation expires. The default expiration time is 24 hours, but you may set it to be as long as 30 days.

Examples:

ssh git@gitolite.kernel.org 2fa val XXXXXX
ssh git@gitolite.kernel.org 2fa val-for-days 30 XXXXXX

Read operations should be completely unaffected.

Supported devices

We implement both HOTP (RFC 4226) and TOTP (RFC 6238) parts of the OATH standard. Since TOTP soft-tokens are easiest to enroll and provision to such a dispersed crowd as kernel developers – and since most kernel developers have access to a smartphone that they carry with them around anyway – TOTP is the preferred mechanism.

TOTP apps

In your smartphone's app directory, you should be able to find one of the following applications (links given to Google Play store, but should exist on iOS as well):

HOTP devices

The only HOTP devices currently tested and supported are yubikeys. Any of the currently listed products should support HOTP authentication:

  • Yubikey 4 either standard or Nano form-factors (also supports OpenPGP functionality)

Laptop users may find that using the Nano form factor is more comfortable.

Provisioning your 2-factor token

There is a special "2fa" command in gitolite, used to interact with the 2-factor validation component. To provision, you submit a command via the gitolite interface.

TOTP soft-token apps

To enroll a TOTP soft-token app, such as FreeOTP or Google Authenticator, run:

ssh git@gitolite.kernel.org 2fa enroll totp

This command outputs the following:

totp enrollment mode selected
New token generated for user mricon

Please make sure "qrencode" is installed.
Run the following commands to display your QR code:
    unset HISTFILE
    qrencode -tANSI -m1 -o- "otpauth://totp/mricon@gitolite.kernel.org?secret=ACHQKMJFHIXJDNRY"
  
If that does not work or if you do not have access to
qrencode or a similar QR encoding tool, then you may
open an INCOGNITO/PRIVATE MODE window in your browser
and paste the following URL:
https://www.google.com/chart?chs=200x200&chld=M|0&cht=qr&chl=otpauth%3A%2F%2Ftotp%2Fmricon%40gitolite.kernel.org%3Fsecret%3DACHQKMJFHIXJDNRY

Scan the resulting QR code with your TOTP app, such as
FreeOTP (recommended), Google Authenticator, Authy, or others.
Please write down/print the following 8-digit scratch tokens.
If you lose your device or temporarily have no access to it, you
will be able to use these tokens for one-time bypass.

Scratch tokens:
19489805
36196876
06341363
70324458
39448548
  
Now run the following command to verify that all went well
    ssh git@gitolite.kernel.org 2fa val [token]

If you need more help, please see the following link:
    https://korg.wiki.kernel.org/userdoc:gitolite_2fa

Please remember to "unset HISTFILE" or your secret will be stored in your ~/.bash_history.

Alternatively, if you absolutely have no other way to locally generate a QR code, it is important to actually open a new "Incognito/Private Mode" window to make sure that the URL containing your 2-factor secret is not saved in your browser history. Note, that if you do use the google link, you'll be giving your 2-factor secret to Google – whatever that implies.

Yubikeys

To initialize a yubikey, run the following command instead. Note, that you will need ykpersonalize to configure your key.

ssh git@gitolite.kernel.org 2fa enroll yubikey

The output of the yubikey command is slightly different:

yubikey enrollment mode selected
New token generated for user mricon

Please make sure "ykpersonalize" has been installed.
Insert your yubikey and, as root, run the following command
to provision the secret into slot 1 (use -2 for slot 2):
    unset HISTFILE
    ykpersonalize -1 -ooath-hotp -oappend-cr -a7fd554b1e4a711155d20e9f9615b0451152db3bb
  
Please write down/print the following 8-digit scratch tokens.
If you lose your device or temporarily have no access to it, you
will be able to use these tokens for one-time bypass.
  
Scratch tokens:
88989251
08286736
73163062
90775064
59235228
  
Now run the following command to verify that all went well
    ssh git@gitolite.kernel.org 2fa val [yubkey button press]

If you need more help, please see the following link:
    https://korg.wiki.kernel.org/userdoc:gitolite_2fa

It is important to use "unset HISTFILE" to make sure the secret isn't saved in your ~/.bash_history. Additionally, you may also omit the -a flag and "ykpersonalize" should prompt you for the secret, in which case paste the string that follows the "-a" (but not "-a" itself).

Testing your 2fa token

You can test things on the special "testing" repository:

git clone git@gitolite.kernel.org:testing
cd testing
git checkout -b [username]

Edit the README file, commit, and try to push:

git push origin [username]

You should get the following back:

Counting objects: 7, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 308 bytes | 0 bytes/s, done.
Total 3 (delta 1), reused 0 (delta 0)
remote: IP address "x.x.x.x" has not been validated.
remote: FATAL: W VREF/2fa: testing mricon DENIED by VREF/2fa
remote: 2-factor verification failed
remote:
remote: Please get your 2-factor authentication token and run:
remote:     ssh git@gitolite.kernel.org 2fa val [token]
remote:
remote: If you need more help, please see the following link:
remote:     https://korg.wiki.kernel.org/index.php/Userdoc:gitolite_2fa
remote:
remote: error: hook declined to update refs/heads/mricon
To git@gitolite.kernel.org:testing
 ! [remote rejected] mricon -> mricon (hook declined)
error: failed to push some refs to 'git@gitolite.kernel.org:testing'

As instructed, run the following:

$ ssh git@gitolite.kernel.org 2fa val [token]
Valid TOTP token within window size used
Adding IP address x.x.x.x until Wed May 28 20:29:31 2014 UTC
GeoIP information for x.x.x.x: Saint-laurent, Quebec, CA

If you now try the push again, it will succeed:

$ git push origin mricon
Counting objects: 7, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 308 bytes | 0 bytes/s, done.
Total 3 (delta 1), reused 0 (delta 0)
remote: Reading /var/lib/gitolite3/repositories/manifest.js.gz
remote: Updating /testing.git in the manifest
remote: Writing new /var/lib/gitolite3/repositories/manifest.js.gz
To git@gitolite.kernel.org:testing
   307ff91..87b27aa  mricon -> mricon

Listing validations and invalidating IPs

To list all allowed validations, run:

$ ssh git@gitolite.kernel.org 2fa list-val
{
    "172.x.x.x": {
        "added": "2014-05-27 20:27:44+00:00",
        "expires": "2014-05-28 20:27:44+00:00"
    },
    "24.x.x.x": {
        "geoip": "Saint-laurent, Quebec, CA",
        "added": "2014-05-27 20:29:31+00:00",
        "expires": "2014-05-28 20:29:31+00:00"
    }
}
Listed non-expired entries only. Run "list-val all" to list all.

Note: this command only works from a whitelisted IP address.

To invalidate an IP, use the "inval" command, e.g.:

$ ssh git@gitolite.kernel.org 2fa inval 24.x.x.x
Force-expired 24.x.x.x

Instead of the IP address, you may also use "myip" to invalidate the current IP you're connecting from, or "all" to force-expire all active IP validations. If you run "inval all purge", this will additionally purge all your current and expired entries – handy if you would like to leave no trace of your travel history.

SSH session validation

If you are travelling and happen to be behind a single NAT exit point with a lot of other people, it is preferable to validate only your SSH session instead of the whole public exit point. This will also help if the exit point is not static but changes between tcp sessions (as is sometimes common in very large NAT-ed networks).

Before you can use this feature, you will need to make sure you enabled ssh multiplexing in the client, by adding the following entries to your gitolite.kernel.org section:

ControlPath ~/.ssh/cm-%r@%h:%p
ControlMaster auto
ControlPersist 30m

You can use longer than 30m if necessary – the session will be validated for up to 8 hours. Please see ssh_access for more ssh setup details.

Using in scripts

You can check if your current IP is valid from inside a script, by using the isval check, e.g. like so:

echo -n "Checking if 2fa validation is current: "
if ! ssh git@gitolite.kernel.org 2fa isval; then
    echo "Error: kernel.org 2fa validation expired"
    exit 1
fi

Note that there's an inherent race condition here: your validation may expire between this check and the actual git push.

Switching devices and Unenrolling

Usually you would need to unenroll only when switching devices. If you still have access to your current device or to the scratch-tokens, you can use them to unprovision your current device by using the "unenroll" command:

$ ssh git@gitolite.kernel.org 2fa unenroll [token]
Valid TOTP token used
Removing the secrets file.
Cleaning up state files.
Expiring all validations.
Force-expired 172.0.0.14.
You have been successfully unenrolled.

You can then use the "enroll" command again in order to provision a new device.

If you do NOT have access to your previous 2-factor device, send a signed email to support and we'll work to re-provision you a new token (once a successfully thorough verification procedure is established and followed).

Requesting 2-factor protection for your repository

During this opt-in period, send mail to support to request that your repository is added to the 2fa list.

userdoc/gitolite_2fa.txt · Last modified: 2018-04-27 21:08 by mricon