在linux系统调用中查找用户名 [英] finding the username in a linux system call

问题描述

我向Linux内核添加了一个如下所示的系统调用:

I have added a system call to Linux kernel that looks like this:

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/cred.h>
#include <asm/uaccess.h>

asmlinkage int sys_os_pid_to_uid(int pid, int* puid)
{
    struct task_struct* task;

    rcu_read_lock();

    for_each_process(task)
    {
        if (task->pid == (pid_t) pid)
        {
            copy_to_user(puid, &(task->cred->uid.val), sizeof(task->cred->uid.val));
        }
    }

    rcu_read_unlock();
    return 0;
}

它获取进程ID(pid)，并确定执行该进程的用户的用户ID(puid).

It gets a process ID (pid) and determines the user ID (puid) of the user who is executing it.

现在，我的问题开始了:我想向该系统调用添加另一个参数，即char *username，它将包含ID为puid的用户的用户名.我在cred.h标头中搜索，但找不到与用户名有关的任何内容. 谁能帮我解决这个问题?

Now, my problem begins: I want to add another argument to this system call, that is, char *username, which will contain the username of the user whose ID is puid. I searched in the cred.h header but was unable to find anything concerned with the username. Can anyone help me solve this?

推荐答案

之所以没有找到它，是因为其中没有一个:task_struct，并且通常来说，内核不保留内存中的信息.关于与给定用户ID对应的用户名.这是完全不必要的，会给界面和代码增加混乱，并且会消耗内存，而没有任何额外的好处:与用户有关的所有内容都使用数字用户ID表示和存储.比较容易，并且可以节省内存.

The reason you didn't find it is because there isn't one: task_struct, and the kernel in general, does not keep in-memory information about the username corresponding to a given user ID. That is utterly unnecessary, would add clutter to the interfaces and code, and would consume memory without any added benefit: everything regarding users is represented and stored with numeric user ids. Comparison is easy and memory is saved.

您不应/不能在系统调用中执行此操作.

You shouldn't / can't do this in a syscall.

我建议您编写一个包装程序用户空间函数，该函数调用您的syscall，然后调用getpwuid(3)或getpwuid_r(3)将用户ID转换为用户名.请注意，这是在用户空间而不是内核空间中完成的.

I suggest you write a wrapper user-space function that invokes your syscall and then calls getpwuid(3) or getpwuid_r(3) to convert from the user ID to the username. Note that this is to be done in user-space, not in kernel space.

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