In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan

l2cap_new_connection() sets default value of channel mode to match the
parent channel.  l2cap_le_connect_req() left this at the default, and
created L2CAP_MODE_EXT_FLOWCTL channels if listening pchan has that
mode.  This causes FLAG_DEFER_SETUP channels to reply to
L2CAP_LE_CONN_REQ with L2CAP_ECRED_CONN_RSP, which is incorrect.

It can also result to stack OOB write (of l2cap_alloc_cid determined
values) in l2cap_ecred_rsp_defer(), as l2cap_le_connect_req() does not
limit maximum number of deferred channels or check for duplicate ident.

Fix by setting chan->mode correctly in l2cap_le_connect_req().

Also check channel mode in l2cap_ecred_rsp_defer(), and do WARN_ON_ONCE
instead of OOB write to make it less brittle.