Bluetooth regression breaking BT connection for all 2.0 and older devices in 5.0.15+, 5.1.x and master

[Hans de Goede]

Hi All,

First of all this is a known issue and it seems a fix is in the works,
but what I do not understand is why the commit causing this has not
simply been reverted until the fix is done, esp. for the 5.0.x
stable series where this was introduced in 5.0.15.

The problem I'm talking about is commit d5bb334a8e17 ("Bluetooth: Align
minimum encryption key size for LE and BR/EDR connections"):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d5bb334a8e171b262e48f378bd2096c0ea458265
basically completely breaking all somewhat older (and some current cheap
no-name) bluetooth devices:

A revert of this was first proposed on May 22nd:
https://lore.kernel.org/netdev/CA+E=qVfopSA90vG2Kkh+XzdYdNn=M-hJN_AptW=R+B5v3HB9eA@xxxxxxxxxxxxxx/T/
We are 18 days further now and this problem still exists, including in the
5.0.15+ and 5.1.x stable kernels.

A solution has been suggested: https://lore.kernel.org/linux-bluetooth/20190522070540.48895-1-marcel@xxxxxxxxxxxx/T/#u
and at least the Fedora 5.1.4+ kernels now carry this as a temporary fix,
but as of today I do not see a fix nor a revert in Torvald's tree yet and
neither does there seem to be any fix in the 5.0.x and 5.1.x stable series.

In the mean time we are getting a lot of bug reports about this:
https://bugzilla.kernel.org/show_bug.cgi?id=203643
https://bugzilla.redhat.com/show_bug.cgi?id=1711468
https://bugzilla.redhat.com/show_bug.cgi?id=1713871
https://bugzilla.redhat.com/show_bug.cgi?id=1713980

And some reporters:
https://bugzilla.redhat.com/show_bug.cgi?id=1713871#c4
Are indicating that the Fedora kernels with the workaround included
still do not work...

As such I would like to suggest that we just revert the troublesome
commit for now and re-add it when we have a proper fix.

Regards,

Hans