linux用户态与内核态通过字符设备交互

本文介绍: Linux内核态与用户态交互之字符设备

通信协议格式

[2bytes数据长度] + |2bytes目录路径数量| + |2bytes 长度| + |目录数据| + ... + |2bytes 长度| + |目录数据|

控制命令定义

#include <linux/ioctl.h>

#define BASEMINOR 0
#define COUNT 5
#define NAME "ioctl_test"

#define IOCTL_TYPE 'k'

//定义无参的命令
#define IOCTL_NO_ARG _IO(IOCTL_TYPE, 1)

//用户空间向内核空间写
#define IOCTL_WRITE_INT _IOW(IOCTL_TYPE, 2,int)

//用户空间从内核空间读
#define IOCTL_READ_INT _IOR(IOCTL_TYPE, 3, int)

//用户空间向内核空间写
#define IOCTL_WRITE_STRING _IOW(IOCTL_TYPE, 4,char*)

//用户空间从内核空间读
#define IOCTL_READ_STRING _IOR(IOCTL_TYPE, 5, char*)


#define IOCTL_MAXNR 5

上述命令实现了用户态向内核态写入、读取int型或string类型的数据，定义控制命令个数为5

用户态程序

#include <stdio.h>
#include <string.h>
#include <linux/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include "cmd.h"
enum arg_type{
	ARG_INT,
	ARG_STRING
};
union data{
		int integer;
		char string[255];
	};

struct arg_node{
	int type; //字符串类型
	union data arg_data;
	struct arg_node*next;
};
void insert_node(struct arg_node**head, struct arg_node * item ){
		if(item==NULL)
		{
			printf("待插入节点指针为空n");
			return ;
		}
		if(*head == NULL){
			*head = item;
			printf("节点指针赋值，%pn",*head);
		}
		else{
			struct arg_node *current = *head;
			while(current->next != NULL){
				current = current->next;
			}
			current->next = item;
		}
	}

//参数格式：user_ipc -int 200 -string "12324154"
int main(int argc, char *argv[])
{
	if(argc<2 || argc%2==0)
	{
		printf("参数个数不匹配n");
		return -1;
	}
	int fd = 0;
	int arg = 0;
	
	fd = open("/dev/ioctl_test", O_RDWR);
	if(fd < 0){
		printf("open memdev0 failed!n");
		return -1;
	}
	if(ioctl(fd, IOCTL_NO_ARG, &arg) < 0){
		printf("----打印命令传输失败----n");
		return -1;
	}
	
	unsigned char *protocol_body = NULL;
	int init_length = 5;
	int realloc_length = 10;
	int len_tag_bytes = 2;
	protocol_body = calloc(init_length, sizeof(unsigned char )*init_length);

	int index = 4;
	int num_of_dirs = 0;
	struct arg_node *p_head = NULL;
	int i=0;
	for(i=1; i<argc; i=i+2){
		if(strcmp(argv[i],"-int") == 0){
					struct arg_node*p_item = malloc(sizeof(struct arg_node));
					p_item->next = NULL;
					p_item->type = ARG_INT;
					p_item->arg_data.integer = atoi(argv[i+1]);
					insert_node(&p_head, p_item);
					printf("插入int类型，值: %d n",p_item->arg_data.integer);
					if(p_head==NULL)
						printf("链表头指针为空n");
		}
		else if(strcmp(argv[i], "-string") == 0){
			struct arg_node *p_item = malloc(sizeof(struct arg_node));
			p_item->next = NULL;		
			p_item->type = ARG_STRING;
			memcpy(p_item->arg_data.string, argv[i+1],strlen(argv[i+1]));
		    insert_node(&p_head, p_item);
			printf("插入string类型，值: %s n",p_item->arg_data.string);

			//插入值组装协议数据包[2bytes数据长度] + [2bytes 字符串数量] +[2bytes长度] + [目录绝对路径] ... + [2bytes长度] + [目录绝对路径]
			int length = strlen(argv[i+1]);
			if((index+len_tag_bytes+length) > init_length) //空间不够，再分配
			{
				realloc_length = length + len_tag_bytes + 1; //计算再分配字节，多分配1个字节，作为结束null
				protocol_body = realloc(protocol_body, sizeof(unsigned char)*(init_length + realloc_length));
				if(!protocol_body){
					printf("再分配空间失败n");
					exit(-1);
				}
				memset(protocol_body+index, 0, sizeof(unsigned char)*(init_length + realloc_length)); //初始化再分配空间为零
				init_length += realloc_length;
				printf("新分配空间成功，新分配空间字节大小 %d，总空间大小 %dn",realloc_length, init_length);

			}
			protocol_body[index] = length / 256 ;
			protocol_body[index + 1] = length % 256;
			index = index + 2;
			memcpy(protocol_body + index, argv[i+1],length);
			index = index + length;
			num_of_dirs++;
		}
	}
	index = index -2;
	protocol_body[0] = index / 256;
	protocol_body[1] = index % 256;
	protocol_body[2] = num_of_dirs /256;
	protocol_body[3] = num_of_dirs %256;

	printf("组包数据：%dn",index);
	for(i=0; i<index+2; i++){
		printf("%02x ",protocol_body[i]);

	}
	printf("n");
	//内核交互 -- 字符设备
	if(ioctl(fd, IOCTL_WRITE_STRING, protocol_body)<0){
	    printf("----用户态向内核写入字符串数据失败----n");
	    return -1;
	 }
	 char recv[256]={0};
	 if(ioctl(fd,IOCTL_READ_STRING,recv)<0){
	    printf("----用户态从内核态读取字符串数据失败----n");
	    return -1;
	}
	printf("从内核态读取数据：%sn",recv);
	//释放申请内存
	free(protocol_body);
	protocol_body = NULL;

	close(fd);
	return 0;
}

上述代码实现把多个int或者char*类型的数据插入链表中，但是实际使用中，这个链表比没有用，和用户态交互，我只使用了string类型的数据，再把数据存入到protocol_body中，通过控制命令IOCTL_WRITE_STRING,实现把protocol_body写入到字符设备，供内核模块读取，同时内核模块返回一个随机数。

编译命令

gcc -o user_ipc user_ipc.c

内核模块

//msg_recv_send.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/io.h>
#include <linux/ioctl.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/unistd.h>
#include <linux/random.h>
#include "cmd.h"
#include "ctl_data.h"



dev_t dev_num;
struct cdev *cdevp = NULL;

/*
struct dir_node{
        int length; //长度
        char *dir_s; //目录字符串
        struct list_head list; //链表
};
*/
LIST_HEAD(msg_list_head);

//处理
int handle_recv_msg(char *msg, int len){
	int ret = 0;
	int dir_index=0;
	//清空链表
	struct dir_node *entry, *tmp;
	
	list_for_each_entry_safe(entry, tmp, &msg_list_head,list){
		list_del(&entry->list);
		kfree(entry->dir_s);
		kfree(entry);
	}
	//解析数据
	int dir_length = 0;
	int num_of_dirs = 0;
	int char_index = 2;
	num_of_dirs = msg[0]<<8 | msg[1];
	for(dir_index=0; dir_index<num_of_dirs; dir_index++){
		dir_length = msg[char_index]<<8 | msg[char_index+1];
		char_index = char_index + 2;
		struct dir_node * new_node = kmalloc(sizeof(struct dir_node),GFP_KERNEL);
		new_node->dir_s = kmalloc(sizeof(char)*(dir_length+1),GFP_KERNEL);
		memset(new_node->dir_s, 0, dir_length+1);
		new_node->length = dir_length;
		INIT_LIST_HEAD(&new_node->list);
		memcpy(new_node->dir_s, msg+char_index, dir_length);
		char_index = char_index + dir_length;
		list_add_tail(&new_node->list, &msg_list_head);
	}
	//遍历列表
	list_for_each_entry(entry, &msg_list_head, list){
		printk(KERN_INFO "接收数据：%sn",entry->dir_s);
	}	
	return ret;
}
static long my_ioctl(struct file * filp, unsigned int cmd, unsigned long arg){
	long ret = 0;
	int err = 0;
	int ioarg = 0;
	char kernel_buffer[256];
	unsigned int random_value = 0;		
	if(_IOC_TYPE(cmd) != IOCTL_TYPE){
		return -EINVAL;
	}
	if(_IOC_NR(cmd) > IOCTL_MAXNR){
		return -EINVAL;
	}
	
	if(_IOC_DIR(cmd) & _IOC_READ){
		err = !access_ok((void*)arg, _IOC_SIZE(cmd));
	}
	else if(_IOC_DIR(cmd) & _IOC_WRITE){
		err = !access_ok((void*)arg, _IOC_SIZE(cmd));
	}

	if(err){
		return -EFAULT;
	}
	switch(cmd){
		case IOCTL_NO_ARG:
			printk(KERN_INFO "print not arg cmdn");
			break;
		case IOCTL_WRITE_INT:
			ret = __get_user(ioarg, (int*)arg);
			printk(KERN_INFO "get data from user space is :%dn", ioarg);
			break;
		case IOCTL_READ_INT:
			ioarg = 1101;
			ret = __put_user(ioarg, (int *)arg);
			break;
		case IOCTL_WRITE_STRING:
			memset(kernel_buffer, 0, sizeof(kernel_buffer));
			unsigned char len[3]={0};

			ret = copy_from_user(len, (char*)arg, 2);
			int recv_len = 0;
			recv_len = len[0]*256 + len[1];
			
			printk(KERN_INFO "用户态写入的数据长度 %d",len[0]*256+len[1]);
			char *recv_buffer = kmalloc(sizeof(char)*recv_len,GFP_KERNEL);
			ret = copy_from_user(recv_buffer, (unsigned char*)(arg+2), recv_len);
			if(ret!=0){
				printk(KERN_INFO "从用户态拷贝数据失败,失败字节数 %dn",ret);
			}
			printk(KERN_INFO "get data from user space is :%*phn",recv_len, recv_buffer);
					
			
			//处理接收到的字符串
			handle_recv_msg(recv_buffer, recv_len);
			kfree(recv_buffer);
			break;
		case IOCTL_READ_STRING:
			//memset(random_value, 0, sizeof(random_value));
			memset(kernel_buffer, 0, sizeof(kernel_buffer));
			random_value = get_random_int();
			snprintf(kernel_buffer, sizeof(kernel_buffer),"返回随机字符串数值：%u",random_value);
			printk(KERN_INFO "kern_buffer : %sn",kernel_buffer);
			ret = copy_to_user((char *)arg,kernel_buffer,sizeof(kernel_buffer));
			if(ret == 0){
				printk(KERN_INFO "写文本字符到用户态成功,[%s]。n",(char*)arg);
			}
			else{
				printk(KERN_INFO "写文本字符到用户态失败，未写入字节数 %d。n",ret);
			}
			break;
		default:
			return -EINVAL;
	}
	return ret;
}

static const struct file_operations fops = {
	.owner = THIS_MODULE,
	.unlocked_ioctl = my_ioctl
};

int __init ioctl_init(void ){
	int ret ;
	ret = alloc_chrdev_region(&dev_num, BASEMINOR, COUNT, NAME);
	if(ret < 0){
		printk(KERN_ERR "alloc_chrdev_region failed...n");
		goto err1;
	}
	printk(KERN_INFO, "major = %dn",MAJOR(dev_num));
    cdevp = cdev_alloc();
	if(NULL == cdevp){
		printk(KERN_ERR "cdev_alloc failed...n");
		ret = -ENOMEM;
		goto err2;
	}
	cdev_init(cdevp, &fops);
	ret = cdev_add(cdevp, dev_num, COUNT);
	if(ret < 0){
		printk(KERN_INFO "cdev_add failed...n");
		goto err2;
	}
	printk(KERN_INFO "------init completelyn");
	return 0;
err2:
		unregister_chrdev_region(dev_num, COUNT);
err1:
	return ret;
}

void __exit ioctl_exit(void){
	cdev_del(cdevp);
	unregister_chrdev_region(dev_num, COUNT);
	printk(KERN_INFO "exit success.");
}

上述代码中alloc_chrdev_region分配一个名为NAME的字符设备，

int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count, const char *name);
//dev 字符设备存储的指针，高12位是主设备号，低20位是从设备号
//baseminor是从设备号
//count 请求的设备号数量
//name  设备名

内核模块主文件

//file_shield.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <asm/unistd.h>
#include <asm/ptrace.h>
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <linux/string.h>
#include <linux/cred.h>
#include "hook_func.h"
#include "ctl_data.h"
#include "msg_recv_send.h"

MODULE_LICENSE("GPL");

//增加字符设备处理逻辑代码

static int __init file_shield_init(void){
	int ret = 0;
	printk(KERN_INFO "init completly");
	//创建字符设备
	ioctl_init();
	printk(KERN_INFO "模块已加载n");
	return ret;
}
static void __exit file_shield_exit(void){
	//卸载字符设备
	ioctl_exit();
	printk(KERN_INFO "模块已卸载n");
}
module_init(file_shield_init);
module_exit(file_shield_exit);

内核模块Makefile

KERNELDIR:=/lib/modules/$(shell uname -r)/build
EXTRA_CFLAGS +=-O1

PWD = $(shell pwd)

obj-m +=file_hook.o
file_hook-objs:=file_shield.o msg_recv_send.o 

all:
	make -C $(KERNELDIR) M=$(PWD) modules
clean:
	make -C $(KERNELDIR) M=$(PWD) clean

编译

sudo make

输出

 LD [M]  /home/admin01/file-shield/file_hook.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC [M]  /home/admin01/file-shield/file_hook.mod.o
  LD [M]  /home/admin01/file-shield/file_hook.ko
make[1]: 离开目录“/usr/src/linux-headers-5.4.18-53-generic”