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, &regs) == -1)
		goto exit;    

	/* save original registers */
	memcpy(&original_regs, &regs, 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, &regs) == -1)
		goto exit;    

	map_base = ptrace_retval(&regs);    

	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, &regs) == -1)
		goto exit;    

	void * sohandle = ptrace_retval(&regs);    

	#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, &regs) == -1)
		goto exit;    

	void * hook_entry_addr = ptrace_retval(&regs);
	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, &regs) == -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, &regs) == -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