Leaving my draft here both so you can read it and so I don't lose it: > Indeed, the reason for this is that in authd we are presenting a qrcode to perform weblogin and that doesn't work.
This seems a reasonable justification for an SRU in principle then, now that it's documented. Thank you for the update. The remaining questions are whether this way of fixing it is the best one for the SRU. And even though I agree the SRU is justified in principle, we should remain open to the possibility that the risk associated with this particular change outweighs the benefits. Given the security sensitive area being touched I'd like a firm +1 from the security team please, that considers both the code changes and the risk. Seth> Are ascii-encoded qr codes known to be insufficient? I think this is a good question but leave it to the desktop team to decide. > The test case for it, in a such complex setup isn't as easy to test as the minimal reproducer that it's enough to cover the fix and to ensure there are no regressions in the normal behavior. I think that's fine for the usual requirement that the test case be reproducible by anybody and it looks like a good initial proxy test for the issue being resolved. However, you're requesting this SRU for a particular purpose, and it's an invasive change. I'd like you to verify that your actual purpose is also fulfilled end-to-end during SRU verification please, to ensure that before we publish to -updates that further tweaks won't be required and there will be no reason to abandon the change. Otherwise we would have burdened users with a download, update and regression risk for no reason. Please add a verification that your final purpose actually works to the Test Plan. If changes to other packages are also needed for that, then they should be tested in -proposed all together. > PAM info messsages are exposed as generic SSH messages, they're the only ones of this kind AFAIK, but I wanted to be generic enough so that normal ssh usage should be checked too. > PAM it is, but keyboard interactive authentication (which is the only case that triggers these messages) is not, so the change doesn't affect PAM behavior of ssh per se, only if the server has enabled keyboard interactive authentication, which PAM modules can trigger. OK, but there are cases where we recommend doing that, such as for HOTP/TOTP configuration: https://ubuntu.com/server/docs/openssh-server. Maybe it's worth adding to the Test Plan to ensure that those steps still work? > So banners and other messages should be checked for regressions. Please could you add steps on how you specifically intend to do this to the Test Plan? I asked around the SRU team for a second opinion, and I got back some additional concerns: 0) This should probably have received a review from the security team before uploading to the development release. 1) If it filtered out control characters and restricted itself to UTF-8 printable that would be less scary. Could you consider that, please? 2) What happens if the client and server encodings do not agree? This isn't entirely theoretical. I'm told that Japan has a national encoding standard that is not Unicode which is still in widespread use and it may be the case that this is still what we use on Ubuntu when installing in Japanese. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to openssh in Ubuntu. https://bugs.launchpad.net/bugs/2077576 Title: SSH client doesn't handle properly non-ASCII chars Status in openssh package in Ubuntu: Fix Released Status in openssh source package in Focal: Incomplete Status in openssh source package in Jammy: Incomplete Status in openssh source package in Noble: Fix Released Bug description: [ Impact ] Non-ascii visible chars (including back-slashes, new lines and so) are not properly rendered by clients, showing their octal visualization. Such as: Hello SSHD \\ We love \360\237\215\225! Instead of: Hello SSHD \ We love 🍕! This is particularly an issue when a server has configured keyboard interactive authentication and a PAM module wants to show non-ASCII characters such as a QR code for web authentication: When using an ubuntu server running authd for web authentication we may end up having the login qrcode rendered such as \210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210 https://ubuntu.com 1337 Which is clearly unreadable. [ Test case ] ## Server preparation Enable PAM and keyboard interactive authentication in a ssh server: Add a configuration file such as: /etc/ssh/sshd_config.d/test-ssh-pam.conf Containing: UsePAM yes KbdInteractiveAuthentication yes # This was working already; here to check potential regressions ForceCommand bash -c "echo Hello from SSHD \ We also love 🍕!; $SHELL" It's also suggested to check for regressions using a `Banner` option in sshd, pointing to a file with utf-8 contents. Restart the server: sudo systemctl restart ssh.service Edit the sshd PAM configuration file, adding as first line: auth requisite pam_echo.so Hello SSHD \ We love 🍕! Can be done with the command: sudo sed '1 iauth requisite pam_echo.so Hello SSHD! \\ We love 🍕!' \ -i /etc/pam.d/sshd ## Client test In the same host: ssh -o PubkeyAuthentication=no \ -o PasswordAuthentication=no \ -o PreferredAuthentications=keyboard-interactive \ $USER@localhost The client should show: Hello SSHD \ We love 🍕! ($USER@localhost) Password: ... Hello from SSHD \ We also love 🍕! Retry the same with another host and without keyboard authentication enabled in the server side. To verify the fix in more complex scenario it's possible to follow the instructions of configuring authd: - https://github.com/ubuntu/authd/wiki/05--How%E2%80%90to-log-in-over-SSH Once authd is configured, the user should be able to scan a QrCode from a ssh session. ## Cleanup Revert the changes done in the cleanup phase, after test is done sudo sed '/pam_echo\.so/d' -i /etc/pam.d/sshd sudo rm /etc/ssh/sshd_config.d/test-ssh-pam.conf [ Regression potential ] SSH info messages are not shown by the client. Even though those aren't covered by this change, it's important to check for regressions in any output that SSH exposes to the user. So banners and other messages should be checked for regressions. These kind of messages are normally shown only when PAM *and* keyboard interaction are enabled in the server side, so it should not affect the default ubuntu servers behavior. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2077576/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
