linux 使用Hook技术 拦截打印机的打印并设置打印水印，给出通用参考代码

以下是一个基于Linux内核的Hook技术拦截打印机的打印并设置打印水印的参考代码：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/usb.h>
#include <linux/usb/hcd.h>
#include <linux/slab.h>

static struct usb_device_id my_usb_ids[] = {
    { USB_DEVICE(0x1234, 0x5678) }, // 根据实际情况修改
    { },
};
MODULE_DEVICE_TABLE(usb, my_usb_ids);

// 自定义的打印函数，用于添加水印信息
static int my_printer_write(struct usb_printer *printer, const char *buf, unsigned count)
{
    char *new_buf;
    int new_count;

    // 分配新的缓冲区，并在原始数据前添加水印信息
    new_buf = kmalloc(count + 16, GFP_KERNEL);
    if (!new_buf)
        return -ENOMEM;
    snprintf(new_buf, 16, "[My Watermark] ");
    memcpy(new_buf + 16, buf, count);
    new_count = count + 16;

    // 调用原始的打印函数进行打印
    return printer->ops->write(printer, new_buf, new_count, 1000);
}

// Hook函数，用于修改打印机的write函数指针
static void hook_printer(struct usb_device *dev)
{
    struct usb_interface_descriptor *intf_desc;
    struct usb_host_interface *iface_desc;
    struct usb_endpoint_descriptor *ep_desc;
    struct usb_printer *printer;
    int i, j, k;

    // 查找打印机接口
    intf_desc = &dev->config->interface[0].altsetting[0];
    iface_desc = &dev->config->interface[0];
    for (i = 0; i < iface_desc->desc.bNumEndpoints; i++) {
        ep_desc = &iface_desc->endpoint[i].desc;
        if ((ep_desc->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) == USB_ENDPOINT_XFER_BULK &&
            (ep_desc->bEndpointAddress & USB_DIR_IN) == 0 &&
            (ep_desc->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK) != 0) {
            // 找到打印机的输出端点，Hook打印函数的write指针
            printer = kmalloc(sizeof(struct usb_printer), GFP_KERNEL);
            if (!printer)
                return;
            memset(printer, 0, sizeof(struct usb_printer));
            printer->dev = dev;
            printer->bulk_out_endpointAddr = ep_desc->bEndpointAddress;
            printer->ops = kmalloc(sizeof(struct usb_printer_operations), GFP_KERNEL);
            if (!printer->ops) {
                kfree(printer);
                return;
            }
            memcpy(printer->ops, &dev->bus->usb_printer_ops, sizeof(struct usb_printer_operations));
            printer->ops->write = my_printer_write;
            dev->bus->usb_printer_ops = *printer->ops;
            kfree(printer->ops);
            kfree(printer);
            printk(KERN_INFO "Hook printer success!\n");
            break;
        }
    }
}

// Hook函数，用于检测设备插入事件
static int my_probe(struct usb_interface *intf, const struct usb_device_id *id)
{
    struct usb_device *dev = interface_to_usbdev(intf);
    hook_printer(dev);
    return 0;
}

static struct usb_driver my_driver = {
    .name = "my_driver",
    .id_table = my_usb_ids,
    .probe = my_probe,
};

static int __init hook_init(void)
{
    return usb_register(&my_driver);
}

static void __exit hook_exit(void)
{
    usb_deregister(&my_driver);
}

module_init(hook_init);
module_exit(hook_exit);
MODULE_LICENSE("GPL");

这个代码演示了如何拦截打印机的打印并添加水印信息。在模块加载时，Hook函数会注册一个USB驱动程序，并在检测到设备插入时调用`hook_printer`函数来Hook打印函数的write指针。在`my_printer_write`函数内添加水印信息后调用原始的打印函数进行打印。需要注意的是，这个代码仅供参考，具体实现需要根据实际情况进行调整。