Android native层动态库注射

1.简单介绍

本文解说在Android native层。root权限下。注射动态库到目标进程，从而hook目标进程中动态库的函数的实现方式。

文中的源代码所有来源于网络。我仅仅是略微加以整理。

环境：Android4.2 源代码下编译，模拟器中执行。

2.代码构成

包括三个模块的代码：

1.inject程序：把动态库libhookhelper注射到目标进程

2.libhookhelper：动态库代码。此部分代码用于改动目标进程中目标函数所在的got表的信息。从而替换掉目标函数。

理解这部分须要一点点elf格式的知识。文章最后会给出链接文档以作參考。

3.libtest：这部分含实用于測试的目标进程的代码。

目标进程调用一个动态库实现打印字符串的功能。无实际意义。仅作測试。

3.代码

3.1 inject程序与Android.mk文件：

inject.c代码例如以下：

#include <stdio.h>
#include <stdlib.h>
#include <asm/user.h>
#include <asm/ptrace.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <dlfcn.h>
#include <dirent.h>
#include <unistd.h>
#include <string.h>
#include <elf.h>
#include <android/log.h>

#if defined(__i386__)
#define pt_regs         user_regs_struct
#endif

#define ENABLE_DEBUG 1

#if ENABLE_DEBUG
#define  LOG_TAG "inject"
#define  LOGD(fmt, args...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG, fmt, ##args)
#define DEBUG_PRINT(format,args...) \
LOGD(format, ##args)
#else
#define DEBUG_PRINT(format,args...)
#endif

#define CPSR_T_MASK     ( 1u << 5 )

const char *libc_path = "/system/lib/libc.so";
const char *linker_path = "/system/bin/linker";

int ptrace_readdata(pid_t pid,  uint8_t *src, uint8_t *buf, size_t size)
{
uint32_t i, j, remain;
uint8_t *laddr;

union u {
long val;
char chars[sizeof(long)];
} d;

j = size / 4;
remain = size % 4;

laddr = buf;

for (i = 0; i < j; i ++) {
d.val = ptrace(PTRACE_PEEKTEXT, pid, src, 0);
memcpy(laddr, d.chars, 4);
src += 4;
laddr += 4;
}

if (remain > 0) {
d.val = ptrace(PTRACE_PEEKTEXT, pid, src, 0);
memcpy(laddr, d.chars, remain);
}

return 0;
}

int ptrace_writedata(pid_t pid, uint8_t *dest, uint8_t *data, size_t size)
{
uint32_t i, j, remain;
uint8_t *laddr;

union u {
long val;
char chars[sizeof(long)];
} d;

j = size / 4;
remain = size % 4;

laddr = data;

for (i = 0; i < j; i ++) {
memcpy(d.chars, laddr, 4);
ptrace(PTRACE_POKETEXT, pid, dest, d.val);

dest  += 4;
laddr += 4;
}

if (remain > 0) {
d.val = ptrace(PTRACE_PEEKTEXT, pid, dest, 0);
for (i = 0; i < remain; i ++) {
d.chars[i] = *laddr ++;
}

ptrace(PTRACE_POKETEXT, pid, dest, d.val);
}

return 0;
}

#if defined(__arm__)
int ptrace_call(pid_t pid, uint32_t addr, long *params, uint32_t num_params, struct pt_regs* regs)
{
uint32_t i;
for (i = 0; i < num_params && i < 4; i ++) {
regs->uregs[i] = params[i];
}

//
// push remained params onto stack
//
if (i < num_params) {
regs->ARM_sp -= (num_params - i) * sizeof(long) ;
ptrace_writedata(pid, (void *)regs->ARM_sp, (uint8_t *)¶ms[i], (num_params - i) * sizeof(long));
}

regs->ARM_pc = addr;
if (regs->ARM_pc & 1) {
/* thumb */
regs->ARM_pc &= (~1u);
regs->ARM_cpsr |= CPSR_T_MASK;
} else {
/* arm */
regs->ARM_cpsr &= ~CPSR_T_MASK;
}

regs->ARM_lr = 0;

if (ptrace_setregs(pid, regs) == -1
|| ptrace_continue(pid) == -1) {
printf("error\n");
return -1;
}

int stat = 0;
waitpid(pid, &stat, WUNTRACED);
while (stat != 0xb7f) {
if (ptrace_continue(pid) == -1) {
printf("error\n");
return -1;
}
waitpid(pid, &stat, WUNTRACED);
}

return 0;
}

#elif defined(__i386__)
long ptrace_call(pid_t pid, uint32_t addr, long *params, uint32_t num_params, struct user_regs_struct * regs)
{
regs->esp -= (num_params) * sizeof(long) ;
ptrace_writedata(pid, (void *)regs->esp, (uint8_t *)params, (num_params) * sizeof(long));

long tmp_addr = 0x00;
regs->esp -= sizeof(long);
ptrace_writedata(pid, regs->esp, (char *)&tmp_addr, sizeof(tmp_addr));

regs->eip = addr;

if (ptrace_setregs(pid, regs) == -1
|| ptrace_continue( pid) == -1) {
printf("error\n");
return -1;
}

int stat = 0;
waitpid(pid, &stat, WUNTRACED);
while (stat != 0xb7f) {
if (ptrace_continue(pid) == -1) {
printf("error\n");
return -1;
}
waitpid(pid, &stat, WUNTRACED);
}

return 0;
}
#else
#error "Not supported"
#endif

int ptrace_getregs(pid_t pid, struct pt_regs * regs)
{
if (ptrace(PTRACE_GETREGS, pid, NULL, regs) < 0) {
perror("ptrace_getregs: Can not get register values");
return -1;
}

return 0;
}

int ptrace_setregs(pid_t pid, struct pt_regs * regs)
{
if (ptrace(PTRACE_SETREGS, pid, NULL, regs) < 0) {
perror("ptrace_setregs: Can not set register values");
return -1;
}

return 0;
}

int ptrace_continue(pid_t pid)
{
if (ptrace(PTRACE_CONT, pid, NULL, 0) < 0) {
perror("ptrace_cont");
return -1;
}

return 0;
}

int ptrace_attach(pid_t pid)
{
if (ptrace(PTRACE_ATTACH, pid, NULL, 0) < 0) {
perror("ptrace_attach");
return -1;
}

int status = 0;
waitpid(pid, &status , WUNTRACED);

return 0;
}

int ptrace_detach(pid_t pid)
{
if (ptrace(PTRACE_DETACH, pid, NULL, 0) < 0) {
perror("ptrace_detach");
return -1;
}

return 0;
}

void* get_module_base(pid_t pid, const char* module_name)
{
FILE *fp;
long addr = 0;
char *pch;
char filename[32];
char line[1024];

if (pid < 0) {
/* self process */
snprintf(filename, sizeof(filename), "/proc/self/maps", pid);
} else {
snprintf(filename, sizeof(filename), "/proc/%d/maps", pid);
}

fp = fopen(filename, "r");

if (fp != NULL) {
while (fgets(line, sizeof(line), fp)) {
if (strstr(line, module_name)) {
pch = strtok( line, "-" );
addr = strtoul( pch, NULL, 16 );

if (addr == 0x8000)
addr = 0;

break;
}
}

fclose(fp) ;
}

return (void *)addr;
}

void* get_remote_addr(pid_t target_pid, const char* module_name, void* local_addr)
{
void* local_handle, *remote_handle;

local_handle = get_module_base(-1, module_name);
remote_handle = get_module_base(target_pid, module_name);

DEBUG_PRINT("[+] get_remote_addr: local[%x], remote[%x]\n", local_handle, remote_handle);

void * ret_addr = (void *)((uint32_t)local_addr + (uint32_t)remote_handle - (uint32_t)local_handle);

#if defined(__i386__)
if (!strcmp(module_name, libc_path)) {
ret_addr += 2;
}
#endif
return ret_addr;
}

int find_pid_of(const char *process_name)
{
int id;
pid_t pid = -1;
DIR* dir;
FILE *fp;
char filename[32];
char cmdline[256];

struct dirent * entry;

if (process_name == NULL)
return -1;

dir = opendir("/proc");
if (dir == NULL)
return -1;

while((entry = readdir(dir)) != NULL) {
id = atoi(entry->d_name);
if (id != 0) {
sprintf(filename, "/proc/%d/cmdline", id);
fp = fopen(filename, "r");
if (fp) {
fgets(cmdline, sizeof(cmdline), fp);
fclose(fp);

if (strcmp(process_name, cmdline) == 0) {
/* process found */
pid = id;
break;
}
}
}
}

closedir(dir);
return pid;
}

long ptrace_retval(struct pt_regs * regs)
{
#if defined(__arm__)
return regs->ARM_r0;
#elif defined(__i386__)
return regs->eax;
#else
#error "Not supported"
#endif
}

long ptrace_ip(struct pt_regs * regs)
{
#if defined(__arm__)
return regs->ARM_pc;
#elif defined(__i386__)
return regs->eip;
#else
#error "Not supported"
#endif
}

int ptrace_call_wrapper(pid_t target_pid, const char * func_name, void * func_addr, long * parameters, int param_num, struct pt_regs * regs)
{
DEBUG_PRINT("[+] Calling %s in target process.\n", func_name);
if (ptrace_call(target_pid, (uint32_t)func_addr, parameters, param_num, regs) == -1)
return -1;

if (ptrace_getregs(target_pid, regs) == -1)
return -1;
DEBUG_PRINT("[+] Target process returned from %s, return value=%x, pc=%x \n",
func_name, ptrace_retval(regs), ptrace_ip(regs));
return 0;
}

int inject_remote_process(pid_t target_pid, const char *library_path,
const char *function_name, const char *param, size_t param_size)
{
int ret = -1;
void *mmap_addr, *dlopen_addr, *dlsym_addr, *dlclose_addr, *dlerror_addr;
void *local_handle, *remote_handle, *dlhandle;
uint8_t *map_base = 0;
uint8_t *dlopen_param1_ptr, *dlsym_param2_ptr, *saved_r0_pc_ptr, *inject_param_ptr, *remote_code_ptr, *local_code_ptr;

struct pt_regs regs, original_regs;
extern uint32_t _dlopen_addr_s, _dlopen_param1_s, _dlopen_param2_s, _dlsym_addr_s, \
_dlsym_param2_s, _dlclose_addr_s, _inject_start_s, _inject_end_s, _inject_function_param_s, \
_saved_cpsr_s, _saved_r0_pc_s;

uint32_t code_length;
long parameters[10];

DEBUG_PRINT("[+] Injecting process: %d\n", target_pid);

if (ptrace_attach(target_pid) == -1)
goto exit;

if (ptrace_getregs(target_pid, ®s) == -1)
goto exit;

/* save original registers */
memcpy(&original_regs, ®s, sizeof(regs));

mmap_addr = get_remote_addr(target_pid, libc_path, (void *)mmap);
DEBUG_PRINT("[+] Remote mmap address: %x\n", mmap_addr);

/* call mmap */
parameters[0] = 0;  // addr
parameters[1] = 0x4000; // size
parameters[2] = PROT_READ | PROT_WRITE | PROT_EXEC;  // prot
parameters[3] =  MAP_ANONYMOUS | MAP_PRIVATE; // flags
parameters[4] = 0; //fd
parameters[5] = 0; //offset

if (ptrace_call_wrapper(target_pid, "mmap", mmap_addr, parameters, 6, ®s) == -1)
goto exit;

map_base = ptrace_retval(®s);

dlopen_addr = get_remote_addr( target_pid, linker_path, (void *)dlopen );
dlsym_addr = get_remote_addr( target_pid, linker_path, (void *)dlsym );
dlclose_addr = get_remote_addr( target_pid, linker_path, (void *)dlclose );
dlerror_addr = get_remote_addr( target_pid, linker_path, (void *)dlerror );

DEBUG_PRINT("[+] Get imports: dlopen: %x, dlsym: %x, dlclose: %x, dlerror: %x\n",
dlopen_addr, dlsym_addr, dlclose_addr, dlerror_addr);

printf("library path = %s\n", library_path);
ptrace_writedata(target_pid, map_base, library_path, strlen(library_path) + 1);

parameters[0] = map_base;
parameters[1] = RTLD_NOW| RTLD_GLOBAL;

if (ptrace_call_wrapper(target_pid, "dlopen", dlopen_addr, parameters, 2, ®s) == -1)
goto exit;

void * sohandle = ptrace_retval(®s);

#define FUNCTION_NAME_ADDR_OFFSET       0x100
ptrace_writedata(target_pid, map_base + FUNCTION_NAME_ADDR_OFFSET, function_name, strlen(function_name) + 1);
parameters[0] = sohandle;
parameters[1] = map_base + FUNCTION_NAME_ADDR_OFFSET;

if (ptrace_call_wrapper(target_pid, "dlsym", dlsym_addr, parameters, 2, ®s) == -1)
goto exit;

void * hook_entry_addr = ptrace_retval(®s);
DEBUG_PRINT("hook_entry_addr = %p\n", hook_entry_addr);

#define FUNCTION_PARAM_ADDR_OFFSET      0x200
ptrace_writedata(target_pid, map_base + FUNCTION_PARAM_ADDR_OFFSET, param, strlen(param) + 1);
parameters[0] = map_base + FUNCTION_PARAM_ADDR_OFFSET;

if (ptrace_call_wrapper(target_pid, "hook_entry", hook_entry_addr, parameters, 1, ®s) == -1)
goto exit;

printf("Press enter to dlclose and detach\n");
getchar();
parameters[0] = sohandle;

if (ptrace_call_wrapper(target_pid, "dlclose", dlclose, parameters, 1, ®s) == -1)
goto exit;
/* restore */
ptrace_setregs(target_pid, &original_regs);
ptrace_detach(target_pid);
ret = 0;

exit:
return ret;
}

int main(int argc, char** argv) {
pid_t target_pid;
if(argc!=2) {
printf("invalid prarams");
}
target_pid = find_pid_of(argv[1]);
if (-1 == target_pid) {
printf("Can't find the process\n");
return -1;
}

inject_remote_process(target_pid, "/system/lib/libhookhelper.so", "hook_entry",  "I'm parameter!", strlen("I'm parameter!"));
return 0;
}

Android.mk文件

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES := inject.c
LOCAL_SHARED_LIBRARIES := libcutils libutils libdl
LOCAL_MODULE := inject

include $(BUILD_EXECUTABLE)

3.2 libhookhelper代码

hookhelper代码例如以下：

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <android/log.h>
#include <elf.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <linker.h>
#include <dlfcn.h>

#define LOG_TAG "hookhelper"
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, fmt, ##args)

extern "C" {
//external function declaration
extern void print();

void newPrint()
{
LOGD("new Print\n");
print();
}

#define LIBSF_PATH      "/system/bin/cqlmain"
#define FUNCTIONNAME    "print"

void *g_OriginalFunc = (void*)print;
void *g_NewFunc = (void*)newPrint;

void* get_module_base(pid_t pid, const char* module_name)
{
FILE *fp;
long addr = 0;
char *pch;
char filename[32];
char line[1024];

if (pid < 0) {
/* self process */
snprintf(filename, sizeof(filename), "/proc/self/maps", pid);
} else {
snprintf(filename, sizeof(filename), "/proc/%d/maps", pid);
}

fp = fopen(filename, "r");

if (fp != NULL) {
while (fgets(line, sizeof(line), fp)) {
if (strstr(line, module_name)) {
pch = strtok( line, "-" );
addr = strtoul( pch, NULL, 16 );

if (addr == 0x8000)
addr = 0;

break;
}
}

fclose(fp) ;
}

return (void *)addr;
}

void replaceFunc(void *handle,const char *name, void* pNewFun, void** pOldFun)
{

if(!handle)
return;

soinfo *si = (soinfo*)handle;
Elf32_Sym *symtab = si->symtab;
const char *strtab = si->strtab;
Elf32_Rel *rel = si->plt_rel;
unsigned count = si->plt_rel_count;
unsigned idx;

bool fit = 0;

for(idx=0; idx<count; idx++)
{
unsigned int type = ELF32_R_TYPE(rel->r_info);
unsigned int sym = ELF32_R_SYM(rel->r_info);
unsigned int reloc = (unsigned)(rel->r_offset + si->base);
char *sym_name = (char *)(strtab + symtab[sym].st_name);

if(strcmp(sym_name, name)==0)
{
uint32_t page_size = getpagesize();
uint32_t entry_page_start = reloc& (~(page_size - 1));
mprotect((uint32_t *)entry_page_start, page_size, PROT_READ | PROT_WRITE);

*pOldFun = (void *)*((unsigned int*)reloc);
*((unsigned int*)reloc)= (unsigned int)pNewFun;
LOGD("find %s function at address: %p\n",name,(void*)*pOldFun);
fit = 1;
break;
}
rel++;
}

if(fit) {
LOGD("not find :%s in plt_rel\n",FUNCTIONNAME);
}
}

void replaceFun2() {
void * base_addr = get_module_base(getpid(), LIBSF_PATH);

LOGD("%s address = %p\n", LIBSF_PATH,base_addr);

int fd;
fd = open(LIBSF_PATH, O_RDONLY);
if (-1 == fd) {
LOGD("error\n");
return;
}

Elf32_Ehdr ehdr;
read(fd, &ehdr, sizeof(Elf32_Ehdr));

unsigned long shdr_addr = ehdr.e_shoff;
int shnum = ehdr.e_shnum;
int shent_size = ehdr.e_shentsize;
unsigned long stridx = ehdr.e_shstrndx;

Elf32_Shdr shdr;
lseek(fd, shdr_addr + stridx * shent_size, SEEK_SET);
read(fd, &shdr, shent_size);

char * string_table = (char *)malloc(shdr.sh_size);
lseek(fd, shdr.sh_offset, SEEK_SET);
read(fd, string_table, shdr.sh_size);
lseek(fd, shdr_addr, SEEK_SET);

int i;
uint32_t out_addr = 0;
uint32_t out_size = 0;
uint32_t got_item = 0;
int32_t got_found = 0;

for (i = 0; i < shnum; i++) {
read(fd, &shdr, shent_size);
if (shdr.sh_type == SHT_PROGBITS) {

int name_idx = shdr.sh_name;
if (strcmp(&(string_table[name_idx]), ".got.plt") == 0
|| strcmp(&(string_table[name_idx]), ".got") == 0) {

out_addr = (uint32_t)(base_addr + shdr.sh_addr);
out_size = shdr.sh_size;

for (i = 0; i < out_size; i += 4) {
got_item = *(uint32_t *)(out_addr + i);
if (got_item  == (uint32_t)g_OriginalFunc) {
LOGD("found %s in got\n",FUNCTIONNAME);

got_found = 1;

uint32_t page_size = getpagesize();
uint32_t entry_page_start = (out_addr + i) & (~(page_size - 1));
mprotect((uint32_t *)entry_page_start, page_size, PROT_READ | PROT_WRITE);

*(uint32_t *)(out_addr + i) = (uint32_t)g_NewFunc;
//break;
} else if (got_item == (uint32_t)g_NewFunc) {
LOGD("Already hooked\n");
got_found = 1;
break;
}
}

if (got_found)
break;
}
}
}

free(string_table);
close(fd);
}

int hook()
{
#if 1
replaceFunc( dlopen( LIBSF_PATH, RTLD_GLOBAL ),
FUNCTIONNAME, g_NewFunc, (void**)&g_OriginalFunc);
#else
replaceFun2();
#endif
return 0;
}

int hook_entry(char * a) {
hook();
return 0;
}

}

Android.mk文件例如以下：

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES := hookhelper.cpp
LOCAL_C_INCLUDES += bionic/linker \

LOCAL_SHARED_LIBRARIES := libcutils libutils libprint libdl
LOCAL_MODULE    := libhookhelper

include $(BUILD_SHARED_LIBRARY)

3.3 libtest文件例如以下：

main.c:

#include <stdio.h>
//#include "print.h"
int main() {
extern void print();
while(1) {
print();
sleep(2);
}
return 0;
}

print.c文件例如以下：

#include<cutils/log.h>
#undef LOG_TAG
#define LOG_TAG "test"
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, fmt, ##args)

void print() {
LOGD("my print :%p\n",(void*)print);
}

Android.mk文件例如以下：

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES := print.c
LOCAL_SHARED_LIBRARIES := libcutils libutils liblog
LOCAL_MODULE    := libprint

include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS)

LOCAL_SRC_FILES := main.c
LOCAL_SHARED_LIBRARIES := libprint
LOCAL_MODULE := cqlmain

include $(BUILD_EXECUTABLE)

4. 參考文档

http://blog.csdn.net/jinzhuojun/article/details/9900105

http://www.xfocus.net/articles/200208/438.html

http://blog.csdn.net/myarrow/article/details/9630377