bug#67012: 29.1; epa-sign-file pinentry loopback mode does not work with S/MIME

[Eli Zaretskii]

> From: Ulrich Mueller <ulm@gentoo.org>
> Date: Thu, 09 Nov 2023 10:46:08 +0100
> 
> Investigating a little further, I see that gpgsm is invoked like this:
> 
>    /usr/bin/gpgsm --no-tty --status-fd 1 --yes --output hello.txt.p7m 
> --pinentry-mode loopback --sign -u XXXXXXXXXXXXXXXX -- hello.txt
> 
> I believe that the --passphrase-fd option is missing there.
> 
> Trying from the command line, the following works:
> 
>    $ /usr/bin/gpgsm --no-tty --status-fd 1 --yes --output hello.txt.p7m 
> --pinentry-mode loopback --passphrase-fd 0 --sign -u XXXXXXXXXXXXXXXX -- 
> hello.txt
> 
> It expects a passphrase from stdin (without a prompt), and after
> entering that, signing will succeed.
> 
> Then again, when I hack function epg--start to add "--passphrase-fd" "0"
> to args, the error no longer occurs, but now gpgsm hangs (waiting for
> input)? Also Emacs doesn't prompt for a passphrase.

Isn't this one more manifestation of the GnuPG 2.4.1?  See the entry
in etc/PROBLEMS whose heading is "Saving a file encrypted with GnuPG
via EasyPG hangs".

IOW, if you downgrade to an older version of GnuPG, do both problems
go away?

Thanks.