irda: Fix memory leak caused by repeated binds of irda socket

The irda_bind() function allocates memory for self->ias_obj without
checking to see if the socket is already bound. A userspace process
could repeatedly bind the socket, have each new object added into the
LM-IAS database, and lose the reference to the old object assigned to
the socket to exhaust memory resources. This patch errors out of the
bind operation when self->ias_obj is already assigned.

CVE-2018-6554

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reviewed-by: Seth Arnold <seth.arnold@canonical.com>
Reviewed-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>