linux修改一下进程

在linux中prctl可以满足这个要求，下满是man手册：

PR_SET_NAME (since Linux 2.6.9)

Set the process name for the calling process, using the value in

the location pointed to by (char *) arg2. The name can be up to

16 bytes long, and should be null terminated if it contains

fewer bytes.

但是prctl修改的进程名，只能是16个字节(包括'\0')。下面是修改的代码（changetitle.c）：

#include <stdio.h>

#include <sys/prctl.h>

int main(int argc, char *argv[], char *envp[])

{

char *new_name = "abcdefghijklmnopqrstuvwxyz"

getchar()

prctl(PR_SET_NAME, new_name)

getchar()

return 0

}

当新名称长度大于16时就会截断，上面的新名字截断后是abcdefghijklmno。这对于我们来说是有缺陷的。而且通过ps -aux 查看，进程名称并没有改变，改变的只是/prco/$(PID)/stat和

/prco/$(PID)/status的值，而/prco/$(PID)/cmdline并没有改变。这种方式使用起来也是不方便的。

下面介绍另一种方式，可以与上面的方式互补。

首先看一下main函数的原型:int main(int argc, char *argv[])

argv[0]存放的是终端执行的程序名称也就是进程名。argv[1...argc-1]存放的是命令行参数。

linux中main()还有一个隐藏参数就是环境变量信息，存放了运行时所需要的环境变量。

我们可以通过以下来访问这个变量

extern char **environ

argv与environ是连续存放在栈区的。下面代码可以查看参数信息：

#include <stdio.h>

#include <string.h>

extern char **environ

int main(int argc , char *argv[])

{

int i

printf("argc:%d\n" , argc)

for (i = 0i <argc++i)

{

printf("argv[%d](0x%x):%s\n" , i , (unsigned int)argv[i], argv[i])

}

printf("evriron=0x%x\n" , (unsigned int)environ[0])

return 0

}

通过上面可以看出，我们只需要修改argv[0]所指向的内存空间的内容，就可以修改进程名。但是如果新名称比argv[0]的长度小，我们可以直接修改，并把多余的部分请0，如果新名称

比argv[0]长我们需要两步：

1、申请新内存保存环境变量信息和argv[1...argc-1]参数信息

2、修改argv[0]，将新名称往后到environ的最后一项清0

以下是参考代码：

#include <unistd.h>

#include <stdio.h>

#include <stdarg.h>

#include <string.h>

#include <stdlib.h>

#include <sys/prctl.h>

# define MAXLINE 2048

extern char **environ

static char **g_main_Argv = NULL/* pointer to argument vector */

static char *g_main_LastArgv = NULL/* end of argv */

void setproctitle_init(int argc, char **argv, char **envp)

{

int i

for (i = 0envp[i] != NULLi++) // calc envp num

continue

environ = (char **) malloc(sizeof (char *) * (i + 1))// malloc envp pointer

for (i = 0envp[i] != NULLi++)

{

environ[i] = malloc(sizeof(char) * strlen(envp[i]))

strcpy(environ[i], envp[i])

}

environ[i] = NULL

g_main_Argv = argv

if (i >0)

g_main_LastArgv = envp[i - 1] + strlen(envp[i - 1])

else

g_main_LastArgv = argv[argc - 1] + strlen(argv[argc - 1])

}

void setproctitle(const char *fmt, ...)

{

char *p

int i

char buf[MAXLINE]

extern char **g_main_Argv

在编写网络服务器程序时，为了响应客户端的请求，我们经常需要新建进程来处理业务流程；而且又是为了关闭某个非法请求或者关闭长连接的客户端，这时就需要杀死进程 killall proc_name。 但是在新建进程时，子进程名与父进程名相同。因此需要由进程名及参数来区分客户端连接。

在linux中prctl可以满足这个要求，下满是man手册：

PR_SET_NAME (since Linux 2.6.9)

Set the process name for the calling process, using the value in

the location pointed to by (char *) arg2. The name can be up to

16 bytes long, and should be null terminated if it contains

fewer bytes.

但是prctl修改的进程名，只能是16个字节(包括'\0')。下面是修改的代码（changetitle.c）：

#include <stdio.h>

#include <sys/prctl.h>

int main(int argc, char *argv[], char *envp[])

{

char *new_name = "abcdefghijklmnopqrstuvwxyz"

getchar()

prctl(PR_SET_NAME, new_name)

getchar()

return 0

}

当新名称长度大于16时就会截断，上面的新名字截断后是abcdefghijklmno。这对于我们来说是有缺陷的。而且通过ps -aux 查看，进程名称并没有改变，改变的只是/prco/$(PID)/stat和

/prco/$(PID)/status的值，而/prco/$(PID)/cmdline并没有改变。这种方式使用起来也是不方便的。

下面介绍另一种方式，可以与上面的方式互补。

首先看一下main函数的原型:int main(int argc, char *argv[])

argv[0]存放的是终端执行的程序名称也就是进程名。argv[1...argc-1]存放的是命令行参数。

linux中main()还有一个隐藏参数就是环境变量信息，存放了运行时所需要的环境变量。

我们可以通过以下来访问这个变量

extern char **environ

argv与environ是连续存放在栈区的。下面代码可以查看参数信息：

#include <stdio.h>

#include <string.h>

extern char **environ

int main(int argc , char *argv[])

{

int i

printf("argc:%d\n" , argc)

for (i = 0i <argc++i)

{

printf("argv[%d](0x%x):%s\n" , i , (unsigned int)argv[i], argv[i])

}

printf("evriron=0x%x\n" , (unsigned int)environ[0])

return 0

}

通过上面可以看出，我们只需要修改argv[0]所指向的内存空间的内容，就可以修改进程名。但是如果新名称比argv[0]的长度小，我们可以直接修改，并把多余的部分请0，如果新名称

比argv[0]长我们需要两步：

1、申请新内存保存环境变量信息和argv[1...argc-1]参数信息

2、修改argv[0]，将新名称往后到environ的最后一项清0

以下是参考代码：

#include <unistd.h>

#include <stdio.h>

#include <stdarg.h>

#include <string.h>

#include <stdlib.h>

#include <sys/prctl.h>

# define MAXLINE 2048

extern char **environ

static char **g_main_Argv = NULL/* pointer to argument vector */

static char *g_main_LastArgv = NULL/* end of argv */

void setproctitle_init(int argc, char **argv, char **envp)

{

int i

for (i = 0envp[i] != NULLi++) // calc envp num

continue

environ = (char **) malloc(sizeof (char *) * (i + 1))// malloc envp pointer

for (i = 0envp[i] != NULLi++)

{

environ[i] = malloc(sizeof(char) * strlen(envp[i]))

strcpy(environ[i], envp[i])

}

environ[i] = NULL

g_main_Argv = argv

if (i >0)

g_main_LastArgv = envp[i - 1] + strlen(envp[i - 1])

else

g_main_LastArgv = argv[argc - 1] + strlen(argv[argc - 1])

}

void setproctitle(const char *fmt, ...)

{

char *p

int i

char buf[MAXLINE]

extern char **g_main_Argv

extern char *g_main_LastArgv

va_list ap

p = buf

va_start(ap, fmt)

vsprintf(p, fmt, ap)

va_end(ap)

i = strlen(buf)

if (i >g_main_LastArgv - g_main_Argv[0] - 2)

{

i = g_main_LastArgv - g_main_Argv[0] - 2

buf[i] = '\0'

}

(void) strcpy(g_main_Argv[0], buf)

p = &g_main_Argv[0][i]

while (p <g_main_LastArgv)

*p++ = '\0'

g_main_Argv[1] = NULL

prctl(PR_SET_NAME,buf)

}

int main(int argc, char *argv[])

{

char argv_buf[MAXLINE] = {0}// save argv paramters

for(int i = 1i <argci++)

{

strcat(argv_buf, argv[i])

strcat(argv_buf, " ")

}

setproctitle_init(argc, argv, environ)

setproctitle("%s@%s %s", "new_name", "ip", argv_buf)

for (int i = 0environ[i] != NULLi++)

free(environ[i])

getchar()

return 0

}

上面的代码使用了prctl和修改argv[0]两种修改方法的结合，通过ps -a 、 ps -ef 、ps -aux、 top 等等命令都只能查询到新进程名，/proc/$PID/ 下的文件也显示了新进程名的信息。

应用场景：

1、标识父子进程名称，防止被误杀

2、构造假的进程名及参数，引导非法进入人员到蜜罐系统，取证

为了执行权限检查，传统的 UNIX 实现区分两种类型的进程：特权进程（其有效用户 ID 为0，称为超级用户或 root），和非特权用户（其有效 UID 非0）。特权进程绕过所有的内核权限检查，而非特权进程受基于进程的认证信息（通常是：有效 UID，有效 GID，和补充组列表）的完整权限检查的支配。

自内核 2.2 版本开始，Linux 将传统上与超级用户关联的特权分为几个单元，称为 capabilities （权能），它们可以被独立的启用或禁用。权能是每个线程的属性。

下面的列表展示了 Linux 上实现的权能，以及每种权能允许的 *** 作或行为：

权能的完整实现需要：

在内核 2.6.24 之前，只有前两个要求能够满足；自内核 2.6.24 开始，所有三个要求都能满足。

每个线程具有三个包含零个或多个上面的权能的权能集合：

A child created via fork(2) inherits copies of its parent's capability sets. See below for a discussion of the treatment of capabilities during execve(2).

Using capset(2), a thread may manipulate its own capability sets (see below).

Since Linux 3.2, the file /proc/sys/kernel/cap_last_cap exposes the numerical value of the highest capability supported by the running kernelthis can be used to determine the highest bit that may be set in a capability set.

Since kernel 2.6.24, the kernel supports associating capability sets with an executable file using setcap(8). The file capability sets are stored in an extended attribute (see setxattr(2)) named security.capability. Writing to this extended attribute requires the CAP_SETFCAP capability. The file capability sets, in conjunction with the capability sets of the thread, determine the capabilities of a thread after an execve(2).

The three file capability sets are:

During an execve(2), the kernel calculates the new capabilities of the process using the following algorithm:

其中：

A privileged file is one that has capabilities or has the set-user-ID or set-group-ID bit set.

In order to provide an all-powerful root using capability sets, during an execve(2):

The upshot of the above rules, combined with the capabilities transformations described above, is that when a process execve(2)s a set-user-ID-root program, or when a process with an effective UID of 0 execve(2)s a program, it gains all capabilities in its permitted and effective capability sets, except those masked out by the capability bounding set. This provides semantics that are the same as those provided by traditional UNIX systems.

The capability bounding set is a security mechanism that can be used to limit the capabilities that can be gained during an execve(2). The bounding set is used in the following ways:

Note that the bounding set masks the file permitted capabilities, but not the inherited capabilities. If a thread maintains a capability in its inherited set that is not in its bounding set, then it can still gain that capability in its permitted set by executing a file that has the capability in its inherited set.

Depending on the kernel version, the capability bounding set is either a system-wide attribute, or a per-process attribute.

In kernels before 2.6.25, the capability bounding set is a system-wide attribute that affects all threads on the system. The bounding set is accessible via the file /proc/sys/kernel/cap-bound. (Confusingly, this bit mask parameter is expressed as a signed decimal number in /proc/sys/kernel/capbound.)

Only the init process may set capabilities in the capability bounding setother than that, the superuser (more precisely: programs with the CAP_SYS_MODULE capability) may only clear capabilities from this set.

On a standard system the capability bounding set always masks out the CAP_SETPCAP capability. To remove this restriction (dangerous!), modify the definition of CAP_INIT_EFF_SET in include/linux/capability.h and rebuild the kernel.

The system-wide capability bounding set feature was added to Linux starting with kernel version 2.2.11.

From Linux 2.6.25, the capability bounding set is a per-thread attribute. (There is no longer a systemwide capability bounding set.)

The bounding set is inherited at fork(2) from the thread's parent, and is preserved across an execve(2).

A thread may remove capabilities from its capability bounding set using the prctl(2) PR_CAPBSET_DROP operation, provided it has the CAP_SETPCAP capability. Once a capability has been dropped from the bounding set, it cannot be restored to that set. A thread can determine if a capability is in its bounding set using the prctl(2) PR_CAPBSET_READ operation.

Removing capabilities from the bounding set is supported only if file capabilities are compiled into the kernel. In kernels before Linux 2.6.33, file capabilities were an optional feature configurable via the CONFIG_SECURITY_FILE_CAPABILITIES option. Since Linux 2.6.33, the configuration option has been removed and file capabilities are always part of the kernel. When file capabilities are compiled into the kernel, the init process (the ancestor of all processes) begins with a full bounding set. If file capabilities are not compiled into the kernel, then init begins with a full bounding set minus CAP_SETPCAP, because this capability has a different meaning when there are no file capabilities.

Removing a capability from the bounding set does not remove it from the thread's inherited set. However it does prevent the capability from being added back into the thread's inherited set in the future.

To preserve the traditional semantics for transitions between 0 and nonzero user IDs, the kernel makes the following changes to a thread's capability sets on changes to the thread's real, effective, saved set, and filesystem user IDs (using setuid(2), setresuid(2), or similar):

If a thread that has a 0 value for one or more of its user IDs wants to prevent its permitted capability set being cleared when it resets all of its user IDs to nonzero values, it can do so using the prctl(2) PR_SET_KEEPCAPS operation or the SECBIT_KEEP_CAPS securebits flag described below.

A thread can retrieve and change its capability sets using the capget(2) and capset(2) system calls. However, the use of cap_get_proc(3) and cap_set_proc(3), both provided in the libcap package, is preferred for this purpose. The following rules govern changes to the thread capability sets:

Starting with kernel 2.6.26, and with a kernel in which file capabilities are enabled, Linux implements a set of per-thread securebits flags that can be used to disable special handling of capabilities for UID 0 (root). These flags are as follows:

Each of the above "base" flags has a companion "locked" flag. Setting any of the "locked" flags is irreversible, and has the effect of preventing further changes to the corresponding "base" flag. The locked flags are: SECBIT_KEEP_CAPS_LOCKED, SECBIT_NO_SETUID_FIXUP_LOCKED, SECBIT_NOROOT_LOCKED, and SECBIT_NO_CAP_AMBIENT_RAISE.

The securebits flags can be modified and retrieved using the prctl(2) PR_SET_SECUREBITS and PR_GET_SECUREBITS operations. The CAP_SETPCAP capability is required to modify the flags.

The securebits flags are inherited by child processes. During an execve(2), all of the flags are preserved, except SECBIT_KEEP_CAPS which is always cleared.

An application can use the following call to lock itself, and all of its descendants, into an environment where the only way of gaining capabilities is by executing a program with associated file capabilities:

For a discussion of the interaction of capabilities and user namespaces, see user_namespaces(7).

No standards govern capabilities, but the Linux capability implementation is based on the withdrawn POSIX.1e draft standardsee ⟨ http://wt.tuxomania.net/publications/posix.1e/ ⟩.

From kernel 2.5.27 to kernel 2.6.26, capabilities were an optional kernel component, and can be enabled/disabled via the CONFIG_SECURITY_CAPABILITIES kernel configuration option.

The /proc/PID/task/TID/status file can be used to view the capability sets of a thread. The /proc/PID/status file shows the capability sets of a process's main thread. Before Linux 3.8, nonexistent capabilities were shown as being enabled (1) in these sets. Since Linux 3.8, all nonexistent capabilities (above CAP_LAST_CAP) are shown as disabled (0).

The libcap package provides a suite of routines for setting and getting capabilities that is more comfortable and less likely to change than the interface provided by capset(2) and capget(2). This package also provides the setcap(8) and getcap(8) programs. It can be found at ⟨ http://www.kernel.org/pub/linux/libs/security/linux-privs ⟩.

Before kernel 2.6.24, and from kernel 2.6.24 to kernel 2.6.32 if file capabilities are not enabled, a thread with the CAP_SETPCAP capability can manipulate the capabilities of threads other than itself. However, this is only theoretically possible, since no thread ever has CAP_SETPCAP in either of these cases:

capsh(1), setpriv(1), prctl(2), setfsuid(2), cap_clear(3), cap_copy_ext(3), cap_from_text(3), cap_get_file(3), cap_get_proc(3), cap_init(3), capgetp(3), capsetp(3), libcap(3), credentials(7), user_namespaces(7), pthreads(7), getcap(8), setcap(8)

include/linux/capability.h in the Linux kernel source tree

This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/ .

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