Android native层动态库注射
1.简介
本文讲解在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。文中的源码全部来源于网络,我只是稍微加以整理。
环境:Android4.2 源码下编译,模拟器中运行。
2.代码构成
包含三个模块的代码:
1.inject程序:把动态库libhookhelper注射到目标进程
2.libhookhelper:动态库代码。此部分代码用于修改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。理解这部分需要一点点elf格式的知识。文章最后会给出链接文档以作参考。
3.libtest:这部分含有用于测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,仅作测试。
3.代码
3.1 inject程序与Android.mk文件:
inject.c代码如下:
#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代码如下:
#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文件如下:
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文件如下:
main.c:
#include <stdio.h> //#include "print.h" int main() { extern void print(); while(1) { print(); sleep(2); } return 0; }
print.c文件如下:
#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文件如下:
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. 参考文档
http://blog.csdn.net/jinzhuojun/article/details/9900105
http://www.xfocus.net/articles/200208/438.html
http://blog.csdn.net/myarrow/article/details/9630377
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