include("./checkyou.php"); if(isset($_GET['filename'])){ $filename = $_GET['filename']; include($filename); } ?>

这是一段 PHP 代码，它包含了一个名为 "checkyou.php" 的文件，并且当通过 GET 请求传递了一个名为 "filename" 的参数时，它会包含该参数所指定的文件。这段代码存在安全风险，因为攻击者可以通过传递恶意的文件名来执行任意代码，例如包含一个恶意的 PHP 文件，从而可能导致服务器被攻击。建议使用白名单机制，限制允许包含的文件名。

相关问题

请问以下<?php if(isset($_GET['a'])) { include $_GET['a']; } ?>这个源码如何设置URL，最后能得到源码<?php function upload_please_by_url($url) { if (1 === preg_match('#^[a-z]{3,5}://#', $url)){ $ch = curl_init($url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); curl_setopt($ch, CURLOPT_FAILONERROR, true); if (false === ($file_data = curl_exec($ch))){ echo "curl failed."; }else{ echo "Flag{******}"; } }else{ echo 'Your URL looks errorneous.'; } } if(isset($_POST["url"])){ // upload_please_by_url($_POST["url"]); } ?>

这段源码可以通过以下URL进行设置：

http://example.com/index.php?a=filename.php

其中，index.php是包含上述代码的文件，filename.php是您要包含的文件名。如果您将此URL复制到浏览器中并访问，将会执行filename.php中的代码，并将结果返回给您。

要使用upload_please_by_url函数，可以通过以下URL进行设置：

http://example.com/index.php

然后，您需要通过POST请求发送一个名为url的参数，该参数包含您要下载的文件的URL。例如：

POST http://example.com/index.php
Content-Type: application/x-www-form-urlencoded

url=http://example.com/myfile.txt

这将会执行upload_please_by_url函数，并将myfile.txt文件下载到您的服务器上。如果下载成功，将会在页面上输出Flag{******}。

Write a program to simulate a process of translation from a logical address to physical address. Assumptions 1. Assume the file la.txt includes the sequence of generated addresses from CPU. 2. Use a part of memory as backing store that store data for a process. 3. The backing store size is 128 bytes 4. The size of process p is 128 bytes. 5. The contents of p is included in a file pdata.bin which is a binary file. 6. Use a part of memory as RAM. The size of physical memory is 256 bytes, from 0 to 255. All the physical memory is available, allocating starting from beginning in sequence. That is, allocate frame 0 first, then frame 1, then frame 2…. 7. The size of a frame is 32 bytes, i.e., 5 bits for the offset in a frame, total number of frames is 8. 8. At beginning, no page table is available for process p. Requirements Write a program to 1. Setup a simulating backing store in memory. Read the data from pdata.bin to this backing store. 2. Initialize a page table for process p, set the frame number to be -1 for each page, indicating that the page is not loaded into memory yet. 3. Read logical addresses one by one from la.txt. 4. For each logical address, a) if its page has been loaded into physical memory, simply find the frame number in the page table, then generate physical address, find and print out the physical address and data inside this address. b) if the page is used for the first time, i.e., in page table, its frame number is -1，then the page that contains this address should be loaded into a free frame in physical memory (RAM). Then update the page table by adding the frame number to the right index in the page table. Then repeat 4a). Refer to Figure 1 for the relationships and how physical memory, backing store, and CPU are simulated. Figure 1 How physical memory, backing store and CPU are simulated in this program assignment Hints: a) use a memory block pointed by a pointer or use an array as a simulation of backing store b) use functions fread or mmap for the binary file read. Search through the Internet for the usage of these functions. c) Use an array to simulate the memory. d) Use bit operators &, |, <<, and >> to get the bits in a logic address or form a physical address e) Use char for the type of data in the process, use unsigned char (8 bits) for the type of address. Coding & Submission 1. Using pure C to finish this program. 2. Put all the codes in one .c file named PA3_#####.c, replace “#####” as the last 5 digits of your student ID. 3. Put pdata.txt and la.txt in the same folder as PA3_#####.c, which the need .txt file can be open directly by filename instead of absolute path. 4. Submit only the .c file mentioned above.使用C语言完成

#include <stdio.h>
#include <stdlib.h>

#define BACKING_STORE_SIZE 128
#define PAGE_SIZE 32
#define NUM_PAGES 4
#define NUM_FRAMES 8
#define FRAME_SIZE 32
#define PHYSICAL_MEMORY_SIZE NUM_FRAMES * FRAME_SIZE

int page_table[NUM_PAGES];
unsigned char backing_store[BACKING_STORE_SIZE];
unsigned char physical_memory[PHYSICAL_MEMORY_SIZE];

void load_page(int page_num, int frame_num) {
    int byte_offset = page_num * PAGE_SIZE;
    int frame_offset = frame_num * FRAME_SIZE;
    for (int i = 0; i < PAGE_SIZE; i++) {
        physical_memory[frame_offset + i] = backing_store[byte_offset + i];
    }
}

int main() {
    FILE *la_file = fopen("la.txt", "r");
    FILE *pdata_file = fopen("pdata.bin", "rb");

    if (la_file == NULL || pdata_file == NULL) {
        printf("Error opening file\n");
        return 1;
    }

    // populate backing store with process data
    fread(backing_store, sizeof(unsigned char), BACKING_STORE_SIZE, pdata_file);

    // initialize page table
    for (int i = 0; i < NUM_PAGES; i++) {
        page_table[i] = -1;
    }

    // read logical addresses from file
    int logical_address;
    while (fscanf(la_file, "%d", &logical_address) != EOF) {
        // calculate page number and offset
        int page_num = logical_address / PAGE_SIZE;
        int page_offset = logical_address % PAGE_SIZE;

        // check if page is in memory
        if (page_table[page_num] != -1) {
            int frame_num = page_table[page_num];
            int physical_address = (frame_num * FRAME_SIZE) + page_offset;
            printf("Logical address: %d, Physical address: %d, Data: %c\n",
                   logical_address, physical_address, physical_memory[physical_address]);
        } else {
            // find a free frame in physical memory
            int free_frame = -1;
            for (int i = 0; i < NUM_FRAMES; i++) {
                if (page_table[i] == -1) {
                    free_frame = i;
                    break;
                }
            }

            // if no free frame is found, use a random one (for simplicity)
            if (free_frame == -1) {
                free_frame = rand() % NUM_FRAMES;
                page_table[free_frame] = -1;
            }

            // load page into free frame
            load_page(page_num, free_frame);
            page_table[page_num] = free_frame;

            // print physical address
            int physical_address = (free_frame * FRAME_SIZE) + page_offset;
            printf("Logical address: %d, Physical address: %d, Data: %c\n",
                   logical_address, physical_address, physical_memory[physical_address]);
        }
    }

    fclose(la_file);
    fclose(pdata_file);

    return 0;
}