RDMA/ucma: Don't allow setting RDMA_OPTION_IB_PATH without an RDMA device

Check to make sure that ctx->cm_id->device is set before we use it.
Otherwise userspace can trigger a NULL dereference by doing
RDMA_USER_CM_CMD_SET_OPTION on an ID that is not bound to a device.

Cc: <stable@vger.kernel.org>
Reported-by: <syzbot+a67bc93e14682d92fc2f@syzkaller.appspotmail.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/ucma.c

@@ -1231,6 +1231,9 @@ static int ucma_set_ib_path(struct ucma_context *ctx,
 	if (!optlen)
 		return -EINVAL;
 
+	if (!ctx->cm_id->device)
+		return -EINVAL;
+
 	memset(&sa_path, 0, sizeof(sa_path));
 
 	sa_path.rec_type = SA_PATH_REC_TYPE_IB;