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From bz1389209 comment 33:
$ pcs quorum device update model \
  "host=$(printf \
    "localhost\n}\nheuristics {\nexec_bar: /usr/bin/sh -c 'echo reboot>>/root/.profile||:'\n")"

Need to check with corosync parser which characters should be disallowed.

This is rather urgent for reasons in [bug 1389209 comment 35].

And rather than being matter of corosync parser, it's a general
deficiency in checking the inputs (possibly from less-privileged
sources, depending on the exact use case) to compose the resulting
corosync.conf from, as currently the precooked configuration
snippets may be injected in "plain unlimited string"-evaluated
instances.

- { anywhere in a line means start of a section -> disallowed
- } anywhere in a line means end of a section -> disallowed
- \n and \r starts a new line which could be used to set its own key-value or section -> disallowed
- : is allowed, as only the first : in a line matters
- # is allowed, as the # only matters when it is the first character in a line (not considering whitespace)
- there is no escaping available

This has already been fixed in RHEL 8: bz1679196.
Due to the current RHEL 7 life cycle stage, there will be no fix for RHEL 7.