This patch fixes the following crash by receiving a invalid message:

[  160.672220] ==================================================================
[  160.676206] BUG: KASAN: user-memory-access in dlm_user_add_ast+0xc3/0x370
[  160.679659] Read of size 8 at addr 00000000deadbeef by task kworker/u32:13/319
[  160.681447]
[  160.681824] CPU: 10 PID: 319 Comm: kworker/u32:13 Not tainted 5.14.0-rc2+ #399
[  160.683472] Hardware name: Red Hat KVM/RHEL-AV, BIOS 1.14.0-1.module+el8.6.0+12648+6ede71a5 04/01/2014
[  160.685574] Workqueue: dlm_recv process_recv_sockets
[  160.686721] Call Trace:
[  160.687310]  dump_stack_lvl+0x56/0x6f
[  160.688169]  ? dlm_user_add_ast+0xc3/0x370
[  160.689116]  kasan_report.cold.14+0x116/0x11b
[  160.690138]  ? dlm_user_add_ast+0xc3/0x370
[  160.690832]  dlm_user_add_ast+0xc3/0x370
[  160.691502]  _receive_unlock_reply+0x103/0x170
[  160.692241]  _receive_message+0x11df/0x1ec0
[  160.692926]  ? rcu_read_lock_sched_held+0xa1/0xd0
[  160.693700]  ? rcu_read_lock_bh_held+0xb0/0xb0
[  160.694427]  ? lock_acquire+0x175/0x400
[  160.695058]  ? do_purge.isra.51+0x200/0x200
[  160.695744]  ? lock_acquired+0x360/0x5d0
[  160.696400]  ? lock_contended+0x6a0/0x6a0
[  160.697055]  ? lock_release+0x21d/0x5e0
[  160.697686]  ? lock_is_held_type+0xe0/0x110
[  160.698352]  ? lock_is_held_type+0xe0/0x110
[  160.699026]  ? ___might_sleep+0x1cc/0x1e0
[  160.699698]  ? dlm_wait_requestqueue+0x94/0x140
[  160.700451]  ? dlm_process_requestqueue+0x240/0x240
[  160.701249]  ? down_write_killable+0x2b0/0x2b0
[  160.701988]  ? do_raw_spin_unlock+0xa2/0x130
[  160.702690]  dlm_receive_buffer+0x1a5/0x210
[  160.703385]  dlm_process_incoming_buffer+0x726/0x9f0
[  160.704210]  receive_from_sock+0x1c0/0x3b0
[  160.704886]  ? dlm_tcp_shutdown+0x30/0x30
[  160.705561]  ? lock_acquire+0x175/0x400
[  160.706197]  ? rcu_read_lock_sched_held+0xa1/0xd0
[  160.706941]  ? rcu_read_lock_bh_held+0xb0/0xb0
[  160.707681]  process_recv_sockets+0x32/0x40
[  160.708366]  process_one_work+0x55e/0xad0
[  160.709045]  ? pwq_dec_nr_in_flight+0x110/0x110
[  160.709820]  worker_thread+0x65/0x5e0
[  160.710423]  ? process_one_work+0xad0/0xad0
[  160.711087]  kthread+0x1ed/0x220
[  160.711628]  ? set_kthread_struct+0x80/0x80
[  160.712314]  ret_from_fork+0x22/0x30

The issue is that we received a DLM message for a user lock but the
destination lock is a kernel lock. Note that the address which is trying
to derefence is 00000000deadbeef, which is in a kernel lock
lkb->lkb_astparam, this field should never be derefenced by the DLM
kernel stack. In case of a user lock lkb->lkb_astparam is lkb->lkb_ua
(memory is shared by a union field). The struct lkb_ua will be handled
by the DLM kernel stack but on a kernel lock it will contain invalid
data and ends in most likely crashing the kernel.

It can be reproduced with two cluster nodes.

node 2:
dlm_tool join test
echo "862 fooobaar 1 2 1" > /sys/kernel/debug/dlm/test_locks
echo "862 3 1" > /sys/kernel/debug/dlm/test_waiters

node 1:
dlm_tool join test

python:
foo = DLM(h_cmd=3, o_nextcmd=1, h_nodeid=1, h_lockspace=0x77222027, \
          m_type=7, m_flags=0x1, m_remid=0x862, m_result=0xFFFEFFFE)
newFile = open("/sys/kernel/debug/dlm/comms/2/rawmsg", "wb")
newFile.write(bytes(foo))
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>