我正在使用一个脚本来运行一个程序,并且通过一个我创建的库,使用LD_PRELOAD来拦截一些调用。它工作得很好,但是在某个时刻,进程调用了clone()函数,之后我失去了拦截接下来步骤的能力(程序再次运行,但没有我的库)。有没有办法解决这个问题?
clone(child_stack,
CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD |
CLONE_SYSVSEM | CLONE_SETTLS | CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID,
parent_tidptr, tls, child_tidptr)
查看克隆参数时,我发现可以追踪子进程,但没有任何与预加载相关的内容。
需要说明的是,我试图截取特定文件描述符上的所有调用,而进程克隆了文件描述符,因此我甚至不确定是否可能在没有克隆标志的情况下实现我想要的目标(问题在于我不理解所有标志)。
更新: 我正在尝试记录由qemu-dm执行的所有活动(由xen运行)。
#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <dlfcn.h>
#include <stdio.h>
#include <stdarg.h>
#define dprintf(...) if(__debug__) { char tmp[256]; int cnt = sprintf(tmp, __VA_ARGS__); _write_f_(2, tmp, cnt); _write_f_(__outfile__, tmp, cnt); }
typedef int (*_open_f_t_)(const char *path, int flags, ...);
typedef int (*_open64_f_t_)(const char *path, int flags, ...);
typedef FILE *(*_fopen_f_t_)(const char *path, const char *mode);
typedef int (*_close_f_t_)(int fd);
typedef ssize_t (*_read_f_t_)(int fd, void *buf, size_t count);
typedef ssize_t (*_write_f_t_)(int fd, const void *buf, size_t count);
typedef off_t (*_lseek_f_t_)(int fd, off_t offset, int whence);
static _open_f_t_ _open_f_ = NULL;
static _open64_f_t_ _open64_f_ = NULL;
static _fopen_f_t_ _fopen_f_ = NULL;
static _close_f_t_ _close_f_ = NULL;
static _read_f_t_ _read_f_ = NULL;
static _write_f_t_ _write_f_ = NULL;
static _lseek_f_t_ _lseek_f_ = NULL;
static int __outfile__ = NULL;
static int __debug__ = 0;
void __init__ ()
{
_open_f_ = (_open_f_t_)dlsym(RTLD_NEXT, "open");
_open64_f_ = (_open64_f_t_)dlsym(RTLD_NEXT, "open64");
_fopen_f_ = (_fopen_f_t_)dlsym(RTLD_NEXT, "fopen");
_close_f_ = (_close_f_t_)dlsym(RTLD_NEXT, "close");
_read_f_ = (_read_f_t_)dlsym(RTLD_NEXT, "read");
_write_f_ = (_write_f_t_)dlsym(RTLD_NEXT, "write");
_lseek_f_ = (_lseek_f_t_)dlsym(RTLD_NEXT, "lseek");
unlink("/tmp/qemu-dm-preload.log");
__outfile__ = _open_f_("/tmp/out-0", O_WRONLY | O_CREAT | O_APPEND);
__debug__ = 1;
}
void __fini__ ()
{
__debug__ = 0;
fsync(__outfile__);
_close_f_(__outfile__);
}
int open(const char *path, int flags, ...)
{
//replace this
int result;
if (flags & O_CREAT)
{
va_list arg;
int mode = 0;
va_start (arg, flags);
mode = va_arg (arg, int);
va_end (arg);
result = _open_f_(path, flags, mode);
dprintf("open(%s, %d, %d) => %d\n", path, flags, mode, result);
} else {
result = _open_f_(path, flags);
dprintf("open(%s, %d) => %d\n", path, flags, result);
}
return result;
}
int open64(const char *path, int flags, ...)
{
//replace this
int result;
if (flags & O_CREAT)
{
va_list arg;
int mode = 0;
va_start (arg, flags);
mode = va_arg (arg, int);
va_end (arg);
result = _open64_f_(path, flags, mode);
dprintf("open(%s, %d, %d) => %d\n", path, flags, mode, result);
} else {
result = _open64_f_(path, flags);
dprintf("open(%s, %d) => %d\n", path, flags, result);
}
return result;
}
FILE * fopen(const char *path, const char *mode)
{
FILE *result = _fopen_f_(path, mode);
dprintf("fopen(%s, %s) => %p\n", path, mode, result);
return result;
}
int close(int fd)
{
//replace this
int result = _close_f_(fd);
dprintf("close(%d) => %d\n", fd, result);
return result;
}
ssize_t read(int fd, void *buf, size_t count)
{
// replace this
ssize_t result = _read_f_(fd, buf, count);
dprintf("read(%d, %p, %lu) => %ld\n", fd, buf, count, result);
return result;
}
ssize_t write(int fd, const void *buf, size_t count)
{
// replace this
ssize_t result = _write_f_(fd, buf, count);
dprintf("write(%d, %p, %lu) => %ld\n", fd, buf, count, result);
return result;
}
off_t lseek(int fd, off_t offset, int whence)
{
// replace this
off_t result = _lseek_f_(fd, offset, whence);
dprintf("lseek(%d, %ld, %d) => %ld\n", fd, offset, whence, result);
return result;
}
使用以下命令编译:gcc -ggdb -shared -fPIC -Wl,-init,__init__ -Wl,-fini,__fini__ -o fileaccesshooks.so -ldl fileaccesshooks.c
包装脚本内容:
#!/bin/bash
export LD_PRELOAD=/home/xception/work/fileaccesshooks.so
exec /usr/lib/xen/bin/qemu-dm-orig "$@"
如下评论所述,任务和进程的环境实际上是相同的(LD_PRELOAD对/proc/8408/task/8526/environ和/proc/8408/environ都是相同的),但在调用clone之后不再记录任何数据。
grep -e "testfile" -e "(11" /tmp/out-0
open(/root/testfile.raw, 2) => 11
read(11, 0x7fffb7259d00, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
read(11, 0x7fba6e341200, 512) => 512
我得到的是这样的结果,但是相比之下,在同一个可执行文件上运行 strace -f
的输出包含了大量的读取和查找操作。
clone
后会发生什么?克隆进程应该具有相同的LD_PRELOAD
环境变量设置;环境不会被修改。 - JoniLD_PRELOAD
(例如LD_PRELOAD=blah.so ./a.out
和LD_PRELOAD=blah.sh; export LD_PRELOAD; ./a.out
)。 - twalberg