add support for protecting references against 'got send -f' to gotd ok op@

switch gotd.conf syntax from 'unix_socket' to 'listen on' ok op@

remove the gotsh group requirement from gotd; any user can now connect Repository access is now controlled by access rules in gotd.conf, and concurrent connections to the gotd socket by local users are limited by the listen process. We should keep refining our anti-DoS measures in the future, but at least we have something in place now. ok jamsek, op

gotd: allow to express timeouts using minutes/hours This allows to use a suffix to indicate the unit of measure, such as "1h" for one hour or "30m" for 30 minutes. The suffix "s" for seconds is also accepted for completeness. ok stsp

introduce connection options to gotd.conf Allow administrators to tweak the default authentication and request timeouts if needed, and to tweak the limit of concurrent connections for specific user accounts. with several tweaks from and ok op@

gotd.conf: complain if a repository lacks a path in the configuration file

switch gotd from chroot(2) to unveil(2) In the future, gotd will fork+exec new processes for each client connection. Using unveil instead of chroot avoids having to start such processes as root. The -portable version could use chroot(2) where no equivalent to unveil(2) exists. A future component which starts new processes will be isolated as a separate process, which could run as root in the -portable version. ok op@

implement per-repository read/write authorization rules in gotd ok op@

gotd.8: Add missing .El; gotd.conf.5: Fix typo EL -> El

introduce gotd(8), a Git repository server reachable via ssh(1) This is an initial barebones implementation which provides the absolute minimum of functionality required to serve got(1) and git(1) clients. Basic fetch/send functionality has been tested and seems to work here, but this server is not yet expected to be stable. More testing is welcome. See the man pages for setup instructions. The current design uses one reader and one writer process per repository, which will have to be extended to N readers and N writers in the future. At startup, each process will chroot(2) into its assigned repository. This works because gotd(8) can only be started as root, and will then fork+exec, chroot, and privdrop. At present the parent process runs with the following pledge(2) promises: "stdio rpath wpath cpath proc getpw sendfd recvfd fattr flock unix unveil" The parent is the only process able to modify the repository in a way that becomes visible to Git clients. The parent uses unveil(2) to restrict its view of the filesystem to /tmp and the repositories listed in the configuration file gotd.conf(5). Per-repository chroot(2) processes use "stdio rpath sendfd recvfd". The writer defers to the parent for modifying references in the repository to point at newly uploaded commits. The reader is fine without such help, because Git repositories can be read without having to create any lock-files. gotd(8) requires a dedicated user ID, which should own repositories on the filesystem, and a separate secondary group, which should not have filesystem-level repository access, and must be allowed access to the gotd(8) socket. To obtain Git repository access, users must be members of this secondary group, and must have their login shell set to gotsh(1). gotsh(1) connects to the gotd(8) socket and speaks Git-protocol towards the client on the other end of the SSH connection. gotsh(1) is not an interactive command shell. At present, authenticated clients are granted read/write access to all repositories and all references (except for the "refs/got/" and the "refs/remotes/" namespaces, which are already being protected from modification). While complicated access control mechanism are not a design goal, making it possible to safely offer anonymous Git repository access over ssh(1) is on the road map.