Strange behaviour surrounding "ssh -T ..." and non-zero exit

[W. Michael Petullo]

I am using Dropbear v2017.75 as found on OpenWrt.

I am building a system around a special shell which exits with the value
of `1' upon encountering certain errors. Let us assume this shell runs
on the host "h." My aim is that the following will print `1' if such an
error occurs (using Dropbear's ssh to Dropbear's sshd):

	echo input | ssh -T h; echo $?

Despite the error occurring, the above command line prints `0' rather
than `1.' Since this triggers the error, I would expect the latter
instead.

When I run this (using Dropbear's ssh to Dropbear's sshd):

	ssh -T h; echo $?

and manually provide the input by typing "input," the result is `1'
as expected.

Something from using "-T" and also taking input from a pipe seems to
cause ssh or sshd to malfunction in the earlier case.

When I repeat these commands using OpenSSH's ssh to connect to Dropbear's
sshd, the output is `1' in both cases. This is the expected behavior.

Does anyone have an idea of what might be causing this? Is there indeed
a bug related to "-T" plus stdin from a pipe?

--
Mike

:wq