NETCONF as an OpenSSH subsystem - #1664
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mattiaswal
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Refactor netopeer2-server to act as an OpenSSH subsystem, similar to how sftp works. The SSH daemon authenticates the user and runs the new libnetconf2 netconf-subsystem helper, which bridges the session to a UNIX socket netopeer2-server listens on. The peer credentials of that socket tell the server who the user is, so NACM works as before, and netopeer2-server no longer needs an SSH implementation (libssh) of its own. The libnetconf2 patches add the helper and the API to create a UNIX endpoint without ietf-netconf-server; the netopeer2 patch teaches the server to use them. Buildroot gets an option for this mode, which the Infix defconfigs select. A build without it keeps libssh, NETCONF over TLS, call-home and netopeer2-cli. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
NETCONF becomes a netconf/enabled toggle under the ssh service, and in the default build depends on it the same way restconf depends on web: confd adds port 830 to the sshd listen addresses, forces the subsystem on that port with a Match block, and starts netopeer2-server with -U on the socket. ietf-netconf-server has nothing left to describe there, so it is not loaded and its factory data goes. The build without the OpenSSH subsystem keeps all of that: confd loads the SSH and TLS modules, ships the endpoint in the factory config, and leaves port 830 to netopeer2-server. The migration therefore comes in two flavours, one converts an old endpoint into netconf/enabled, the other only adds the leaf. sshd runs subsystems through the login shell, so the clish wrapper lets the helper through, and only the helper, when called with -c. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
syslogd starts in runlevel S and sshd not before runlevel 2, so the condition never held anything back. It did cost us: a configuration change that touches both, a hostname change together with an SSH change, reloads syslogd, which puts the condition in flux and pauses sshd; with Finit 4.x a second reload arriving right then loses sshd's pending reload, and it keeps its old listen addresses. NETCONF over sshd makes that a lockout. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
A service paused by a condition during a reload lost its own pending reload if another reload came in before it resumed. With NETCONF on sshd this shows up as a lockout: a hostname change together with an SSH change leaves sshd on its old listen addresses. Upstream commit f6b394e0 on the 4.x branch. Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
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Description
With this PR, NETCONF is served by the OpenSSH daemon as a subsystem instead of
libsshembedded innetopeer2-server.sshdauthenticates the user and runs a small libnetconf2 helper that bridges the session to a UNIX socket netopeer2-server listens on. The server learns the user from the socket peer credentials, so NACM works as before.Changes
netconf-subsystemhelper-U PATHfor a UNIX-only endpoint,ietf-netconf-server.yangoptionalBR2_PACKAGE_LIBNETCONF2_SSH_SUBSYSTEMoption, selected by the Infix defconfigs/ssh/netconf/enabled(default true), independent of SSH logins: with logins disabled sshd keeps running on port 830 onlyssh -s <host> netconfalso works on the regular SSH portsclishlogin shell lets the subsystem helper throughBenefits
libssh;netopeer2-serverlinks onlylibnetconf2,libyang,sysrepoandlibcurl/sshietf-netconf-server.yangand its SSH/TLS models are gone from the default builds, less to configure and explainTrade-offs
netopeer2-cliare no longer available in default builds. A build withoutBR2_PACKAGE_LIBNETCONF2_SSH_SUBSYSTEMbrings backlibssh, TLS, call-home, the CLI andietf-netconf-server.yangietf-netconf-serverendpoint. Builds that turn the option off must add it backChecklist
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