so注入(inject)和挂钩(hook) 以及同进程动态库so文件的函数hook方法介绍

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so注入(inject)和挂钩(hook)

- For both x86 and arm对于Android for arm上的so注入（inject）和挂钩（hook），网上已有牛人给出了代码-libinject（http://bbs.pediy.com/showthread.php?t=141355）。由于实现中的ptrace函数是依赖于平台的，所以不经改动只能用于arm平台。本文将之扩展了一下，使它能够通用于Android的x86和arm平台。Arm平台部分基本重用了libinject中的代码，其中因为汇编不好移植且容易出错，所以把shellcode.s用ptrace_call替换掉了，另外保留了mmap，用来传字符串参数，当然也可以通过栈来传，但栈里和其它东西混一起，一弄不好就会隔儿了，所以还是保险点好。最后注意设备要root。首先创建目录及文件：jni
inject.c
Android.mk
Application.mkinject.c:#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;
target_pid = find_pid_of("/system/bin/surfaceflinger");
if (-1 == target_pid) {
printf("Can't find the process\n");
return -1;
}
//target_pid = find_pid_of("/data/test");
inject_remote_process(target_pid, "/data/libhello.so", "hook_entry", "I'm parameter!", strlen("I'm parameter!"));
return 0;
}
注意上面的/system/bin/surfaceflinger进程我随手写的，你的设备上不一定有。没有的话挑其它的也行，前提是ps命令里能找到。
Android.mk:LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := inject
LOCAL_SRC_FILES := inject.c

#shellcode.s

LOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -llog

#LOCAL_FORCE_STATIC_EXECUTABLE := true

include $(BUILD_EXECUTABLE)
Application.mk:APP_ABI := x86 armeabi-v7a
运行nkd-build编译成生x86和arm平台下的可执行文件：jzj@jzj-laptop:~/workspace/inject_hook/inject_jni$ ndk-build
Install : inject => libs/x86/inject
Install : inject => libs/armeabi-v7a/inject

再来生成要注入的so，创建目录及文件：jni
hello.c
Android.mk
Application.mkhello.c:#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <android/log.h>
#include <elf.h>
#include <fcntl.h>

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

int hook_entry(char * a){
LOGD("Hook success, pid = %d\n", getpid());
LOGD("Hello %s\n", a);
return 0;
}
Android.mk:LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -llog
#LOCAL_ARM_MODE := arm
LOCAL_MODULE := hello
LOCAL_SRC_FILES := hello.c
include $(BUILD_SHARED_LIBRARY)

Application.mk:APP_ABI := x86 armeabi-v7a
运行nkd-build编译成生x86和arm平台下的so：jzj@jzj-laptop:~/workspace/inject_hook/hook_so_simple$ ndk-build
Install : libhello.so => libs/x86/libhello.so
Install : libhello.so => libs/armeabi-v7a/libhello.so

然后就可以跑起来试试了，连接root过的Android设备或者打开模拟器。将inject和libhello.so拷入设备，设执行权限，执行：


先看看被注入进程（surfaceflinger）的mmap，可以看到我们的so已经被加载了，紧接着的那一块就是我们mmap出来的：

从logcat中也可以看到so注入成功，并且以被注入进程的身份执行了so中的代码：


同进程动态库so文件的函数hook方法
简单的注入成功，现在我们再来做一个实验，就是应用这套机制来截获surfaceflinger中的eglSwapBuffers调用，然后用我们自己的函数来替换掉原来的eglSwapBuffers调用。关于截系统中的函数调用网上有例子http://bbs.pediy.com/showthread.php?t=157419，这里依葫芦画瓢。首先将hello.c改下：#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <android/log.h>
#include <EGL/egl.h>
#include <GLES/gl.h>
#include <elf.h>
#include <fcntl.h>
#include <sys/mman.h>

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

EGLBoolean (*old_eglSwapBuffers)(EGLDisplay dpy, EGLSurface surf) = -1;

EGLBoolean new_eglSwapBuffers(EGLDisplay dpy, EGLSurface surface)
{
LOGD("New eglSwapBuffers\n");
if (old_eglSwapBuffers == -1)
LOGD("error\n");
return old_eglSwapBuffers(dpy, surface);
}

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;
}

#define LIBSF_PATH "/system/lib/libsurfaceflinger.so"
int hook_eglSwapBuffers()
{
old_eglSwapBuffers = eglSwapBuffers;
LOGD("Orig eglSwapBuffers = %p\n", old_eglSwapBuffers);
void * base_addr = get_module_base(getpid(), LIBSF_PATH);
LOGD("libsurfaceflinger.so address = %p\n", base_addr);

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

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 = base_addr + shdr.sh_addr;
out_size = shdr.sh_size;
LOGD("out_addr = %lx, out_size = %lx\n", out_addr, out_size);

for (i = 0; i < out_size; i += 4) {
got_item = *(uint32_t *)(out_addr + i);
if (got_item == old_eglSwapBuffers) {
LOGD("Found eglSwapBuffers in got\n");
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) = new_eglSwapBuffers;

break;
} else if (got_item == new_eglSwapBuffers) {
LOGD("Already hooked\n");
break;
}
}
if (got_found)
break;
}
}
}

free(string_table);
close(fd);
}

int hook_entry(char * a){
LOGD("Hook success\n");
LOGD("Start hooking\n");
hook_eglSwapBuffers();
return 0;
}
其实这种查找方法有点简单粗暴，要是正式应用的话可以在动态符号表中查找这个符号的got地址。
接着Android.mk改为：LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_LDLIBS += -L$(SYSROOT)/usr/lib -llog -lEGL
#LOCAL_ARM_MODE := arm
LOCAL_MODULE := hello
LOCAL_SRC_FILES := hello.c
include $(BUILD_SHARED_LIBRARY)
Application.mk :
APP_ABI := x86 armeabi-v7a
APP_PLATFORM := android-14
运行ndk-build编译：jzj@jzj-laptop:~/workspace/inject_hook/hook_so$ ndk-build
Install : libhello.so => libs/x86/libhello.so
Install : libhello.so => libs/armeabi-v7a/libhello.so
和上面一样运行，查看logcat，我们可以看到surfaceflinger中调用eglSwapBuffers的地址已被替换成我们的版本：D/INJECT ( 2231): [+] Injecting process: 1728
D/INJECT ( 2231): [+] get_remote_addr: local[b7e4f000], remote[b7e73000]
D/INJECT ( 2231): [+] Remote mmap address: b7e9fe32
D/INJECT ( 2231): [+] Calling mmap in target process.
D/INJECT ( 2231): [+] Target process returned from mmap, return value=b4f1c000, pc=0
D/INJECT ( 2231): [+] get_remote_addr: local[b7f00000], remote[b7f7e000]
D/INJECT ( 2231): [+] get_remote_addr: local[b7f00000], remote[b7f7e000]
D/INJECT ( 2231): [+] get_remote_addr: local[b7f00000], remote[b7f7e000]
D/INJECT ( 2231): [+] get_remote_addr: local[b7f00000], remote[b7f7e000]
D/INJECT ( 2231): [+] Get imports: dlopen: b7f84f50, dlsym: b7f84fd0, dlclose: b7f84de0, dlerror: b7f84dc0
D/INJECT ( 2231): [+] Calling dlopen in target process.
D/INJECT ( 2231): [+] Target process returned from dlopen, return value=b7f995ec, pc=0
D/INJECT ( 2231): [+] Calling dlsym in target process.
D/INJECT ( 2231): [+] Target process returned from dlsym, return value=b4f17e10, pc=0
D/INJECT ( 2231): hook_entry_addr = 0xb4f17e10
D/DEBUG ( 1728): Hook success
D/DEBUG ( 1728): Start hooking
D/DEBUG ( 1728): Orig eglSwapBuffers = 0xb7d4a9c0
D/DEBUG ( 1728): libsurfaceflinger.so address = 0xb7f22000
D/DEBUG ( 1728): out_addr = b7f7aff4, out_size = 624
D/DEBUG ( 1728): Found eglSwapBuffers in got
...
D/DEBUG ( 1728): New eglSwapBuffers
D/DEBUG ( 1728): New eglSwapBuffers
D/DEBUG ( 1728): New eglSwapBuffers
...

[/code]