Any qrexec call from DispVM to opener VM kills DispVM

[rustybird]

Qubes OS version:

R4.0, latest current-testing (but it's not a new problem)

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Steps to reproduce the behavior:

1. Open a terminal in any VM (called "sourcevm" in this example)
2. In that terminal, run qvm-run-vm --dispvm '/usr/lib/qubes/qrexec-client-vm \$default qubes.Filecopy </dev/null; echo sleeping supposedly forever; sleep inf'
3. In the dom0 permission / VM selection dialog that pops up, choose sourcevm and confirm.

Expected behavior:

The qvm-run-vm command should block forever (because of the sleep inf at the end).

Actual behavior:

The qvm-run-vm command finishes a few seconds after showing the "sleeping supposedly forever" message, because the DispVM is killed for some reason.

Last line in /var/log/qubes/qrexec.dispNNNN.log says libvchan_is_eof.

General notes:

If any other VM than sourcevm is chosen the dom0 dialog, everything works as expected (i.e. the DispVM is not killed).

[marmarek]

Duplicate of #3318