Bluetooth: Fix handling of unexpected SMP PDUs

Bluetooth: Fix handling of unexpected SMP PDUs

commit 8cf9fa1240229cbdd888236c0c43fcbad680cf00 upstream.

The conn->smp_chan pointer can be NULL if SMP PDUs arrive at unexpected
moments. To avoid NULL pointer dereferences the code should be checking
for this and disconnect if an unexpected SMP PDU arrives. This patch
fixes the issue by adding a check for conn->smp_chan for all other PDUs
except pairing request and security request (which are are the first
PDUs to come to initialize the SMP context).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>