[Bug 2829] New: ssh.c:process_config_files and readconf.c:process_config_line_depth interpret ~ differently

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=2829

            Bug ID: 2829
           Summary: ssh.c:process_config_files and
                    readconf.c:process_config_line_depth interpret ~
                    differently
           Product: Portable OpenSSH
           Version: 7.4p1
          Hardware: amd64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: martin.von.wittich at iserv.eu

In our company, we use multiple root accounts (that is, accounts with
uid 0) with different user names and home directories for remote
administration purposes. This is mainly so that each user can have his
own personal home directory for configs etc.

Unfortunately, when reading ~/.ssh/config, ssh interprets ~ as the home
directory specified in /etc/passwd for the current user's uid. This
causes it to always read /root/.ssh/config instead of my own personal
config $HOME/.ssh/config. I do not know for sure if this behavior is
intentional, but I suspect this might be for security reasons (so as
not to trust $HOME?). I would very much appreciate it if this behavior
could be changed (most other programs will use $HOME), but I would of
course understand if that's not going to happen.

While reading in the code I discovered something interesting though.
There is a glob() function in openbsd-compat/glob.c that does interpret
~ as $HOME, and via grep I've figured out that readconf.c uses this
function when parsing Include statements. To test this, I created the
following /root/.ssh/config:

server ~ # cat /root/.ssh/config 
Include ~/.ssh/config

And sure enough, now ssh will happily read my ~/.ssh/config:

server ~ # ssh -v example.com
OpenSSH_7.4p1 Debian-10+deb9u2, OpenSSL 1.0.2l  25 May 2017
debug1: Reading configuration data /root/.ssh/config
debug1: Reading configuration data
/var/lib/iserv/remote-support/iserv-martin.von.wittich/.ssh/config
debug1:
/var/lib/iserv/remote-support/iserv-martin.von.wittich/.ssh/config line
1: Applying options for example.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *

I'm still hoping that the ssh behaviour might be changed to that it
will interpret ~ as $HOME, but ssh does in fact shun $HOME for security
reasons, then Include should probably behave the same way.

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