3 ms·

Handy stuff. This would be good for restricting service accounts. There is a whole lot that SSH can do that most people don't know about.

m463 1y ago
> There is a whole lot that SSH can do that most people don't know about. I had to port ssh to embedded hardware decades ago, and pulling back the curtains I came to the opinion that everything was a mess. for example, I needed to be able to upload/download firmware, and was surprised to find that scp wasn't a pure file transfer protocol. It is more like "log into the remote system via shell and run a file transfer program" There are lots of other things I didn't like, like wholesale transferring environment variables back and forth, weird shell interactions and more. It is very useful, but it is an organically grown program, not a designed protocol.
- woooooo 1y ago
  Scp not needing its own protocol is a feature and not a bug in my book..
  - m463 1y ago
    thing is, there IS a transfer protocol, there are just no controls on the files. If you can log in, there is just passing security. Just take a step back and think what you could do if it were a protocol: - limit visible files - limit access to files by user - make access strictly read-only - allow upload-only (sort of a dropbox) - clear separation between login access and file access - remove login user from the whole mess - trivially tie in as a filesystem. etc...
    - rad_gruchalski 1y ago
      But why? It can be done with ssh and some mix of linux permissions. It’s simple. There’s always room for more complexity.
      - m463 1y ago
        I like the simplicity of controlling everything with a hypothetical scp.conf: default access none /dev /sys /proc user foo access ro /var/scp/firmware access rw /var/scp/user-foo user anonymous access w /var/scp/dropbox user joe access rw /home/joe user fred access rw / user backup access ro /
        unsnap_biceps 1y ago
        You can actually switch the subsystem to `internal-sftp` and configure the visible path via ChrootDirectory, however you still rely on posix user/group privs. Subsystems are pluggable, so you could write your own subsystem that does enforce whatever config and permission model you want. It's not terribly difficult to do, and you can replace the sftp subsystem entirely. and just a FYI, currently scp is plumbed over the sftp subsystem, so replacing the sftp subsystem would "fix" scp and sftp clients for you.

m463 1y ago

> There is a whole lot that SSH can do that most people don't know about. I had to port ssh to embedded hardware decades ago, and pulling back the curtains I came to the opinion that everything was a mess. for example, I needed to be able to upload/download firmware, and was surprised to find that scp wasn't a pure file transfer protocol. It is more like "log into the remote system via shell and run a file transfer program" There are lots of other things I didn't like, like wholesale transferring environment variables back and forth, weird shell interactions and more. It is very useful, but it is an organically grown program, not a designed protocol.

woooooo 1y ago
Scp not needing its own protocol is a feature and not a bug in my book..
- m463 1y ago
  thing is, there IS a transfer protocol, there are just no controls on the files. If you can log in, there is just passing security. Just take a step back and think what you could do if it were a protocol: - limit visible files - limit access to files by user - make access strictly read-only - allow upload-only (sort of a dropbox) - clear separation between login access and file access - remove login user from the whole mess - trivially tie in as a filesystem. etc...
  - rad_gruchalski 1y ago
    But why? It can be done with ssh and some mix of linux permissions. It’s simple. There’s always room for more complexity.
    - m463 1y ago
      I like the simplicity of controlling everything with a hypothetical scp.conf: default access none /dev /sys /proc user foo access ro /var/scp/firmware access rw /var/scp/user-foo user anonymous access w /var/scp/dropbox user joe access rw /home/joe user fred access rw / user backup access ro /
      - unsnap_biceps 1y ago
        You can actually switch the subsystem to `internal-sftp` and configure the visible path via ChrootDirectory, however you still rely on posix user/group privs. Subsystems are pluggable, so you could write your own subsystem that does enforce whatever config and permission model you want. It's not terribly difficult to do, and you can replace the sftp subsystem entirely. and just a FYI, currently scp is plumbed over the sftp subsystem, so replacing the sftp subsystem would "fix" scp and sftp clients for you.