ipmi: Rework user message limit handling

commit b52da405 upstream

This patch required quite a bit of work to backport due to a number
of unrelated changes that do not make sense to backport.  This has
been run against my test suite and passes all tests.

The limit on the number of user messages had a number of issues,
improper counting in some cases and a use after free.

Restructure how this is all done to handle more in the receive message
allocation routine, so all refcouting and user message limit counts
are done in that routine.  It's a lot cleaner and safer.

Reported-by: Gilles BULOZ <gilles.buloz@kontron.com>
Closes: https://lore.kernel.org/lkml/aLsw6G0GyqfpKs2S@mail.minyard.net/


Fixes: 8e76741c ("ipmi: Add a limit on the number of users that may use IPMI")
Cc: <stable@vger.kernel.org> # 4.19
Signed-off-by: Corey Minyard <corey@minyard.net>
Tested-by: Gilles BULOZ <gilles.buloz@kontron.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>