misc/vmw_vmci: fix an infoleak in vmci_host_do_receive_datagram()

`struct vmci_event_qp` allocated by qp_notify_peer() contains padding,
which may carry uninitialized data to the userspace, as observed by
KMSAN:

  BUG: KMSAN: kernel-infoleak in instrument_copy_to_user ./include/linux/instrumented.h:121
   instrument_copy_to_user ./include/linux/instrumented.h:121
   _copy_to_user+0x5f/0xb0 lib/usercopy.c:33
   copy_to_user ./include/linux/uaccess.h:169
   vmci_host_do_receive_datagram drivers/misc/vmw_vmci/vmci_host.c:431
   vmci_host_unlocked_ioctl+0x33d/0x43d0 drivers/misc/vmw_vmci/vmci_host.c:925
   vfs_ioctl fs/ioctl.c:51
  ...

  Uninit was stored to memory at:
   kmemdup+0x74/0xb0 mm/util.c:131
   dg_dispatch_as_host drivers/misc/vmw_vmci/vmci_datagram.c:271
   vmci_datagram_dispatch+0x4f8/0xfc0 drivers/misc/vmw_vmci/vmci_datagram.c:339
   qp_notify_peer+0x19a/0x290 drivers/misc/vmw_vmci/vmci_queue_pair.c:1479
   qp_broker_attach drivers/misc/vmw_vmci/vmci_queue_pair.c:1662
   qp_broker_alloc+0x2977/0x2f30 drivers/misc/vmw_vmci/vmci_queue_pair.c:1750
   vmci_qp_broker_alloc+0x96/0xd0 drivers/misc/vmw_vmci/vmci_queue_pair.c:1940
   vmci_host_do_alloc_queuepair drivers/misc/vmw_vmci/vmci_host.c:488
   vmci_host_unlocked_ioctl+0x24fd/0x43d0 drivers/misc/vmw_vmci/vmci_host.c:927
  ...

  Local variable ev created at:
   qp_notify_peer+0x54/0x290 drivers/misc/vmw_vmci/vmci_queue_pair.c:1456
   qp_broker_attach drivers/misc/vmw_vmci/vmci_queue_pair.c:1662
   qp_broker_alloc+0x2977/0x2f30 drivers/misc/vmw_vmci/vmci_queue_pair.c:1750

  Bytes 28-31 of 48 are uninitialized
  Memory access of size 48 starts at ffff888035155e00
  Data copied to user address 0000000020000100

Use memset() to prevent the infoleaks.

Also speculatively fix qp_notify_peer_local(), which may suffer from the
same problem.

Reported-by: syzbot+39be4da489ed2493ba25@syzkaller.appspotmail.com
Cc: stable <stable@kernel.org>
Fixes: 06164d2b ("VMCI: queue pairs implementation.")
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Link: https://lore.kernel.org/r/20221104175849.2782567-1-glider@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/vmw_vmci/vmci_queue_pair.c

@@ -854,6 +854,7 @@ static int qp_notify_peer_local(bool attach, struct vmci_handle handle)
 	u32 context_id = vmci_get_context_id();
 	struct vmci_event_qp ev;
 
+	memset(&ev, 0, sizeof(ev));
 	ev.msg.hdr.dst = vmci_make_handle(context_id, VMCI_EVENT_HANDLER);
 	ev.msg.hdr.src = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
 					  VMCI_CONTEXT_RESOURCE_ID);
@@ -1467,6 +1468,7 @@ static int qp_notify_peer(bool attach,
 	 * kernel.
 	 */
 
+	memset(&ev, 0, sizeof(ev));
 	ev.msg.hdr.dst = vmci_make_handle(peer_id, VMCI_EVENT_HANDLER);
 	ev.msg.hdr.src = vmci_make_handle(VMCI_HYPERVISOR_CONTEXT_ID,
 					  VMCI_CONTEXT_RESOURCE_ID);