C LKM linux_-dirent实现

作为一项安全性研究，我试图实现一个包装系统调用。根据getdents文档，您必须实现自己的linux目录结构。这一切似乎都起作用了，但我无法正确读取linux目录名称

linux驱动程序的实现：

struct mylkm_linux_dirent {
    u64            d_ino;
    s64            d_off;
    unsigned short d_reclen;
    char           d_name[];
};

已包装的getdents调用：

/*
This method will call the original and then sift through results.
Method will remove results that contain the specified keyword.
*/
asmlinkage long mylkm_getdents(unsigned int fd, struct mylkm_linux_dirent * dirp, unsigned int count)
{
    unsigned int size = 0;
    unsigned int bpos = 0;
    struct mylkm_linux_dirent* dir1 = NULL;
    char * buffer_ptr = NULL;
    char hide[] = "mylkm";

    printk("mylkm: getdents() called - redirecting to original sys call.\n");
    size = (*k_getdents)(fd, dirp, count);
    printk("mylkm: bytes value returned by original getdents() call: %ld\n", size);
    printk("mylkm: count value passed into original getdents() call: %i\n", count);
    printk("mylkm: dirp pointer value: %p\n", dirp);

    for (bpos = 0; bpos<size;)
    {
        buffer_ptr = (char*)(&dirp + bpos);
        dir1 = (struct mylkm_linux_dirent*)buffer_ptr;
        printk("mylkm: record length: %d\n", dir1->d_reclen);
        printk("mylkm: record name: %s\n", dir1->d_name);
        printk("mylkm: offset to next dirent: %lld\n", (long long)dir1->d_off);

        bpos += dir1->d_reclen;
    }

    printk("mylkm: Completed mylkm_getdents() call\n");
    return 0;
}

我已经尝试将dir1->d_名称显式转换为char指针。将char指针传入原始调用时崩溃。如何获得正确的列表？

解决方案是：

使用适当的指针算法获取dirp数组的元素。例如

buffer_ptr = ((char*)dirp) + bpos;
dir1 = (struct mylkm_linux_dirent*)buffer_ptr;

通过“从用户复制”功能访问阵列元素，而不是直接访问。例如

u64 reclen; # Record length will be stored here
get_user(&reclen, &dir1->d_reclen); # TODO: check possible errors
printk("mylkm: record length: %d\n", reclen);

# Allocate a structure in the kernel
struct mylkm_linux_dirent* dir1_kernel = kmalloc(reclen, GFP_KERNEL); # TODO: check possible errors
# and copy user-space structure into it.
copy_from_user(dir1_kernel, dir1, reclen); # TODO: check possible errors

# Use dir1_kernel instead of dir
printk("mylkm: record name: %s\n", dir1_kernel->d_name);

# Free kernel structure at the end of the loop
kfree(dir1_kernel);

---

缓冲区\u ptr=char*&dirp+bpos；-这是否曾经编译过，dirp是指向结构的指针，因此结构中添加了一个数字？在右边，您可能需要char*dirp+bpos，它首先将指针转换为指向char的指针，然后用它进行算术运算。并检查它是否与系统调用的dirp参数一致，即在第一次迭代时dir1应等于dirp；在下一次迭代中，dir1应该等于它以前的值加上以前的记录长度。@Tsyvarev我同意。。。该程序因char*dirp+BPO而崩溃。与尝试将指针强制转换为结构mylkm_linux_dirent*@Tsyvarev时一样，我将检查这一点。我还将手动增加指针位置，并尝试获取reclen和name变量，对于u long为4字节，对于u short为2字节。reclen=dirp+bpos+8；name=dirp+bpos+10；printkmylkm:记录长度：%d\n，重新打开；printkmylkm:记录名称：%s\n，名称；char*name变量的打印输出崩溃。雷肯成功了。

u64 reclen; # Record length will be stored here
get_user(&reclen, &dir1->d_reclen); # TODO: check possible errors
printk("mylkm: record length: %d\n", reclen);

# Allocate a structure in the kernel
struct mylkm_linux_dirent* dir1_kernel = kmalloc(reclen, GFP_KERNEL); # TODO: check possible errors
# and copy user-space structure into it.
copy_from_user(dir1_kernel, dir1, reclen); # TODO: check possible errors

# Use dir1_kernel instead of dir
printk("mylkm: record name: %s\n", dir1_kernel->d_name);

# Free kernel structure at the end of the loop
kfree(dir1_kernel);