[Bug 203997] [REGRESSION] Unable to connect BT audio device on 5.1.15

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https://bugzilla.kernel.org/show_bug.cgi?id=203997

--- Comment #8 from Matias Karhumaa (matias.karhumaa@gmail.com) ---
Ah, I think recent regression fix [1] caused another bug:

--snip--
static bool l2cap_check_enc_key_size(struct hci_conn *hcon)
{
        /* The minimum encryption key size needs to be enforced by the
         * host stack before establishing any L2CAP connections. The
         * specification in theory allows a minimum of 1, but to align
         * BR/EDR and LE transports, a minimum of 7 is chosen.
         *
         * This check might also be called for unencrypted connections
         * that have no key size requirements. Ensure that the link is
         * actually encrypted before enforcing a key size.
         */
        return (!test_bit(HCI_CONN_ENCRYPT, &hcon->flags) ||
                hcon->enc_key_size > HCI_MIN_ENC_KEY_SIZE);
}
--snip--

If Encryption key size is 7, L2CAP connection will fail. I think it should be
something like this:

In l2cap_core.c

static bool l2cap_check_enc_key_size(struct hci_conn *hcon)
{
        /* The minimum encryption key size needs to be enforced by the
         * host stack before establishing any L2CAP connections. The
         * specification in theory allows a minimum of 1, but to align
         * BR/EDR and LE transports, a minimum of 7 is chosen.
         *
         * This check might also be called for unencrypted connections
         * that have no key size requirements. Ensure that the link is
         * actually encrypted before enforcing a key size.
         */
        return (!test_bit(HCI_CONN_ENCRYPT, &hcon->flags) ||
                hcon->enc_key_size >= HCI_MIN_ENC_KEY_SIZE);
}
--snip--

Could you test the fix?

[1]:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/net/bluetooth?id=693cd8ce3f882524a5d06f7800dd8492411877b3

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