Linux PAM 验证

Myth丶恋晨 2022-06-04 05:48 232阅读 0赞

*   *  一、什么是PAM验证
     *  二、PAM层次结构
     *  三、PAM工作原理
     *  四、PAM配置
        
         *  4.1 PAM配置文件格式
         *  4.2 PAM的模块类型
         *  4.3 PAM的控制标记
         *  4.4 模块路径及模块参数
     *  五、PAM应用程序开发
        
         *  5.1 预备知识
            
             *  5.1.1 头文件
             *  5.1.2 struct pam\_conv
             *  5.1.3 相关函数
         *  5.2 利用已有的PAM模块编写登陆验证
         *  5.3 自定义PAM模块编写登陆验证

--------------------

## 一、什么是PAM验证 ##

Linux-PAM(linux可插入认证模块)是一套**共享库**，使本地系统管理员可以随意选择程序的认证方式。换句话说，不用重新编译一个包含PAM功能的应用程序，就可以改变它使用的认证机制。应用程序只需调用API就可方便的使用PAM提供的各种认证功能，而无需了解底层的实现。这种方式下,就算升级本地认证机制,也不用修改程序。

像我们使用su命令时，系统会提示你输入root用户的密码，这就是su命令通过调用PAM模块实现的。

--------------------

## 二、PAM层次结构 ##

PAM API是应用程序层与PAM服务模块之间联系的纽带，起着承上启下的作用。系统管理员通过PAM配置文件来制定不同应用程序的不同认证策略。

当应用程序调用PAM API时，应用接口层按照配置文件`pam.conf`的规定，加载相应的PAM服务模块。当PAM服务模块完成相应的认证操作之后，将结果返回给应用接口层。

![PAM层次结构][PAM]

--------------------

## 三、PAM工作原理 ##

1.用户调用某个应用程序，以得到某种服务

2.PAM应用程序调用后台的PAM库进行认证工作

3.PAM库到`/etc/pam.d/`目录查找有关程序配置来确定认证机制

4.PAM库装载所需的认证模块

5.上述装载的认证模块让PAM与应用程序中的会话函数进行通信

6.会话函数向用户要求有关信息

7.用户对这些要求做出回应，提供所需信息

8.PAM认证模块通过PAM库将认证信息提供给应用程序

9.认证完成后，应用程序做出两种选择：

*  认证成功：将所需权限赋予用户，并通知用户
 *  认证失败：通知用户

![PAM工作原理][PAM 1]

--------------------

## 四、PAM配置 ##

### 4.1 PAM配置文件格式 ###

PAM配置文件有两种写法，第一种是写在`/etc/pam.conf`文件中，但这种方法现在**已被废弃**，不再介绍。

第二种是在`/etc/pam.d`目录中，**使用应用程序名作为配置文件名：**

![pam.d][]

配置格式形如：

auth required pam_stack.so service=system-auth

其中：

*  auth 模块类型
 *  required 控制标记
 *  pam\_stack.so 模块路径
 *  service=system-auth 模块参数

### 4.2 PAM的模块类型 ###

Linux PAM有以下四种模块类型，分别代表四种不同的任务：

<table> 
 <thead> 
  <tr> 
   <th align="left">管理方式</th> 
   <th align="left">说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">auth</td> 
   <td align="left">用来对用户的身份进行识别.如:提示用户输入密码,或判断用户是否为root等</td> 
  </tr> 
  <tr> 
   <td align="left">account</td> 
   <td align="left">对帐号的各项属性进行检查.如:是否允许登录,是否达到最大用户数,或是root用户是否允许在这个终端登录等</td> 
  </tr> 
  <tr> 
   <td align="left">session</td> 
   <td align="left">这个模块用来定义用户登录前的,及用户退出后所要进行的操作.如:登录连接信息,用户数据的打开与关闭,挂载文件系统等</td> 
  </tr> 
  <tr> 
   <td align="left">password</td> 
   <td align="left">使用用户信息来更新。如修改用户密码</td> 
  </tr> 
 </tbody> 
</table>

### 4.3 PAM的控制标记 ###

PAM使用控制标记来**处理和判断各个模块的返回值**：

<table> 
 <thead> 
  <tr> 
   <th align="left">控制标记</th> 
   <th align="left">说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">required</td> 
   <td align="left">表示即使某个模块对用户的验证失败，也要等所有的模块都执行完毕后,PAM才返回错误信息。这样做是为了不让用户知道被哪个模块拒绝。如果对用户验证成功，所有的模块都会返回成功信息。</td> 
  </tr> 
  <tr> 
   <td align="left">requisite</td> 
   <td align="left">与required相似,但是如果这个模块返回失败，则立刻向应用程序返回失败，表示此类型失败。不再进行同类型后面的操作</td> 
  </tr> 
  <tr> 
   <td align="left">sufficient</td> 
   <td align="left">表示如果一个用户通过这个模块的验证，PAM结构就立刻返回验证成功信息（即使前面有模块fail了，也会把 fail结果忽略掉），把控制权交回应用程序。后面的层叠模块即使使用requisite或者required 控制标志，也不再执行。如果验证失败，sufficient 的作用和 optional 相同</td> 
  </tr> 
  <tr> 
   <td align="left">optional</td> 
   <td align="left">示即使本行指定的模块验证失败，也允许用户接受应用程序提供的服务，一般返回PAM_IGNORE(忽略)</td> 
  </tr> 
 </tbody> 
</table>

### 4.4 模块路径及模块参数 ###

（1）模块路径

即要调用模块的位置。 对于64为Ubuntu，一般保存在`/lib/x86_64-linux-gnu/security`，如: `pam_unix.so`。

同一个模块，可以出现在不同的类型中。每个模块针对不同的模块类型，编制了不同的执行函数。

（2）模块参数

即传递给模块的参数.参数可以有多个,之间用**空格**分隔开。

（3）常用的PAM模块

![PAM模块][PAM 2]

--------------------

## 五、PAM应用程序开发 ##

### 5.1 预备知识 ###

#### 5.1.1 头文件 ####

#include <security/pam_appl.h>
    #include <security/pam_misc.h>
    #include <security/pam_modules.h>

如果提示找不到头文件，需要先安装一下：

> sudo apt-get install libpam0g-dev

#### 5.1.2 struct pam\_conv ####

这个结构体用于与PAM通信，因为其中比较复杂，我们只列出我们要用到的：

static struct pam_conv conv = {
        misc_conv,
        NULL
    };

#### 5.1.3 相关函数 ####

以下函数具有相同的返回值，这里先说明下：

*  **PAM\_SUCCESS**: Successful completion
 *  **PAM\_ABORT**: Genaral failure
 *  **PAM\_SYSTEM\_ERR**: System error
 *  **PAM\_BUF\_ERR**: Memort buffer error

/* service_name: /etc/pam.d中注册的服务名 user: 要验证的用户名 */
    int pam_start(const char *service_name, const char *user,
                         const struct pam_conv *pam_conversation,
                         pam_handle_t **pamh);
    
    /* flags: 一般为0 */
    int pam_authenticate(pam_handle_t *pamh, int flags);
    
    /* flags: 一般为0 */
    int pam_acct_mgmt(pam_handle_t *pamh, int flags);
    
    /* pam_status：为验证函数的返回值，即pam_authenticate或pam_acct_mgmt的返回值 */
    int pam_end(pam_handle_t *pamh, int pam_status);
    
    /* errnum: 错误值 */
    const char *pam_strerror(pam_handle_t *pamh, int errnum);

### 5.2 利用已有的PAM模块编写登陆验证 ###

首先在`/etc/pam.d`中注册服务，服务名为`my_pam`，我们利用已有的模块`pam_unix.so`：

wxs@ubuntu:/etc/pam.d$ vim my_pam
    wxs@ubuntu:/etc/pam.d$ cd /etc/pam.d/
    wxs@ubuntu:/etc/pam.d$ sudo vim my_pam
    wxs@ubuntu:/etc/pam.d$ 
    wxs@ubuntu:/etc/pam.d$ cat my_pam 
    auth required /lib/x86_64-linux-gnu/security/pam_unix.so
    account required /lib/x86_64-linux-gnu/security/pam_unix.so

编写test.c文件来测试：

#include <stdio.h>
    #include <stdlib.h>
    #include <security/pam_appl.h>
    #include <security/pam_misc.h>
    #include <security/pam_modules.h>
    
    #define MAXSIZE 128
    #define SERVICE_NAME "myPam"
    
    int main(void) {
        int res;
        char user_name[MAXSIZE];
        pam_handle_t *handle;
        static struct pam_conv conv = {
            misc_conv,
            NULL
        };
    
        printf("UserName: ");
        scanf("%s", user_name); 
    
        /* 1.初始化PAM模块 */
        res = pam_start(SERVICE_NAME, user_name, &conv, &handle);
        if (res == PAM_SUCCESS)
            puts("pam service start!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        /* 2.PAM的auth类型验证接口 */
        res = pam_authenticate(handle, 0);
        if (res == PAM_SUCCESS)
            puts("passwd authenticate success!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        /* 3.PAM的account类型验证接口 */
        res = pam_acct_mgmt(handle, 0);
        if (res == PAM_SUCCESS)
            puts("account mgmt success!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        /* 4.PAM模块结束，释放资源 */
        res = pam_end(handle, res);
        if (res == PAM_SUCCESS)
            puts("pam service end!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        return 0;
    }

生成可执行文件：

> gcc test.c -lpam -lpam\_misc -ldl -o test

因为该程序要查询`/etc/passwd`和`/etc/shadow文件`，因此要么执行时加上sudo，要么`sudo chown root.root test`，不然可能会出现错误。运行结果如下：

![运行结果1][1]

### 5.3 自定义PAM模块编写登陆验证 ###

引入头文件`pam_private.h`：

/* * pam_private.h * * This is the Linux-PAM Library Private Header. It contains things * internal to the Linux-PAM library. Things not needed by either an * application or module. * * Please see end of file for copyright. * * Creator: Marc Ewing. * Maintained: CVS */
    
    #ifndef _PAM_PRIVATE_H
    #define _PAM_PRIVATE_H
    
    //#include "config.h"
    
    #include <syslog.h>
    
    #include <security/pam_appl.h>
    #include <security/pam_modules.h>
    #include <security/pam_ext.h>
    
    /* the Linux-PAM configuration file */
    
    #define PAM_CONFIG "/etc/pam.conf"
    #define PAM_CONFIG_D "/etc/pam.d"
    #define PAM_CONFIG_DF "/etc/pam.d/%s"
    
    #define PAM_DEFAULT_SERVICE "other" /* lower case */
    #define PAM_DEFAULT_SERVICE_FILE PAM_CONFIG_D "/" PAM_DEFAULT_SERVICE
    
    #ifdef PAM_LOCKING
    /* * the Linux-PAM lock file. If it exists Linux-PAM will abort. Use it * to block access to libpam */
    #define PAM_LOCK_FILE "/var/lock/subsys/PAM"
    #endif
    
    /* components of the pam_handle structure */
    
    #define _PAM_INVALID_RETVAL -1 /* default value for cached_retval */
    
    struct handler {
        int handler_type;
        int (*func)(pam_handle_t *pamh, int flags, int argc, char **argv);
        int actions[_PAM_RETURN_VALUES];
        /* set by authenticate, open_session, chauthtok(1st) consumed by setcred, close_session, chauthtok(2nd) */
        int cached_retval; int *cached_retval_p;
        int argc;
        char **argv;
        struct handler *next;
        char *mod_name;
        int stack_level;
    };
    
    #define PAM_HT_MODULE 0
    #define PAM_HT_MUST_FAIL 1
    #define PAM_HT_SUBSTACK 2
    #define PAM_HT_SILENT_MODULE 3
    
    struct loaded_module {
        char *name;
        int type; /* PAM_STATIC_MOD or PAM_DYNAMIC_MOD */
        void *dl_handle;
    };
    
    #define PAM_MT_DYNAMIC_MOD 0
    #define PAM_MT_STATIC_MOD 1
    #define PAM_MT_FAULTY_MOD 2
    
    struct handlers {
        struct handler *authenticate;
        struct handler *setcred;
        struct handler *acct_mgmt;
        struct handler *open_session;
        struct handler *close_session;
        struct handler *chauthtok;
    };
    
    struct service {
        struct loaded_module *module; /* Array of modules */
        int modules_allocated;
        int modules_used;
        int handlers_loaded;
    
        struct handlers conf;        /* the configured handlers */
        struct handlers other;       /* the default handlers */
    };
    
    /* * Environment helper functions */
    
    #define PAM_ENV_CHUNK 10 /* chunks of memory calloc()'d *
                      * at once                          */
    
    struct pam_environ {
        int entries;                 /* the number of pointers available */
        int requested;               /* the number of pointers used: * * 1 <= requested <= entries */
        char **list;                 /* the environment storage (a list * * of pointers to malloc() memory) */
    };
    
    #include <sys/time.h>
    
    typedef enum { PAM_FALSE, PAM_TRUE } _pam_boolean;
    
    struct _pam_fail_delay {
        _pam_boolean set;
        unsigned int delay;
        time_t begin;
        const void *delay_fn_ptr;
    };
    
    /* initial state in substack */
    struct _pam_substack_state {
        int impression;
        int status;
    };
    
    struct _pam_former_state {
    /* this is known and set by _pam_dispatch() */
        int choice;            /* which flavor of module function did we call? */
    
    /* state info for the _pam_dispatch_aux() function */
        int depth;             /* how deep in the stack were we? */
        int impression;        /* the impression at that time */
        int status;            /* the status before returning incomplete */
        struct _pam_substack_state *substates; /* array of initial substack states */
    
    /* state info used by pam_get_user() function */
        int fail_user;
        int want_user;
        char *prompt;          /* saved prompt information */
    
    /* state info for the pam_chauthtok() function */
        _pam_boolean update;
    };
    
    struct pam_handle {
        char *authtok;
        unsigned caller_is;
        struct pam_conv *pam_conversation;
        char *oldauthtok;
        char *prompt;                /* for use by pam_get_user() */
        char *service_name;
        char *user;
        char *rhost;
        char *ruser;
        char *tty;
        char *xdisplay;
        char *authtok_type;          /* PAM_AUTHTOK_TYPE */
        struct pam_data *data;
        struct pam_environ *env;      /* structure to maintain environment list */
        struct _pam_fail_delay fail_delay;   /* helper function for easy delays */
        struct pam_xauth_data xauth;        /* auth info for X display */
        struct service handlers;
        struct _pam_former_state former;  /* library state - support for event driven applications */
        const char *mod_name;   /* Name of the module currently executed */
        int mod_argc;               /* Number of module arguments */
        char **mod_argv;            /* module arguments */
        int choice;         /* Which function we call from the module */
    
    #ifdef HAVE_LIBAUDIT
        int audit_state;             /* keep track of reported audit messages */
    #endif
    };
    
    /* Values for select arg to _pam_dispatch() */
    #define PAM_NOT_STACKED 0
    #define PAM_AUTHENTICATE 1
    #define PAM_SETCRED 2
    #define PAM_ACCOUNT 3
    #define PAM_OPEN_SESSION 4
    #define PAM_CLOSE_SESSION 5
    #define PAM_CHAUTHTOK 6
    
    #define _PAM_ACTION_IS_JUMP(x) ((x) > 0)
    #define _PAM_ACTION_IGNORE 0
    #define _PAM_ACTION_OK -1
    #define _PAM_ACTION_DONE -2
    #define _PAM_ACTION_BAD -3
    #define _PAM_ACTION_DIE -4
    #define _PAM_ACTION_RESET -5
    /* Add any new entries here. Will need to change ..._UNDEF and then * need to change pam_tokens.h */
    #define _PAM_ACTION_UNDEF -6 /* this is treated as an error
                           ( = _PAM_ACTION_BAD) */
    
    #define PAM_SUBSTACK_MAX_LEVEL 16 /* maximum level of substacks */
    
    /* character tables for parsing config files */
    extern const char * const _pam_token_actions[-_PAM_ACTION_UNDEF];
    extern const char * const _pam_token_returns[_PAM_RETURN_VALUES+1];
    
    /* * internally defined functions --- these should not be directly * called by applications or modules */
    int _pam_dispatch(pam_handle_t *pamh, int flags, int choice);
    
    /* Free various allocated structures and dlclose() the libs */
    int _pam_free_handlers(pam_handle_t *pamh);
    
    /* Parse config file, allocate handler structures, dlopen() */
    int _pam_init_handlers(pam_handle_t *pamh);
    
    /* Set all hander stuff to 0/NULL - called once from pam_start() */
    void _pam_start_handlers(pam_handle_t *pamh);
    
    /* environment helper functions */
    
    /* create the environment structure */
    int _pam_make_env(pam_handle_t *pamh);
    
    /* delete the environment structure */
    void _pam_drop_env(pam_handle_t *pamh);
    
    /* these functions deal with failure delays as required by the authentication modules and application. Their *interface* is likely to remain the same although their function is hopefully going to improve */
    
    /* reset the timer to no-delay */
    void _pam_reset_timer(pam_handle_t *pamh);
    
    /* this sets the clock ticking */
    void _pam_start_timer(pam_handle_t *pamh);
    
    /* this waits for the clock to stop ticking if status != PAM_SUCCESS */
    void _pam_await_timer(pam_handle_t *pamh, int status);
    
    typedef void (*voidfunc(void))(void);
    typedef int (*servicefn)(pam_handle_t *, int, int, char **);
    
    #ifdef PAM_STATIC
    /* The next two in ../modules/_pam_static/pam_static.c */
    
    /* Return pointer to data structure used to define a static module */
    struct pam_module * _pam_open_static_handler (pam_handle_t *pamh,
                              const char *path);
    
    /* Return pointer to function requested from static module */
    
    voidfunc *_pam_get_static_sym(struct pam_module *mod, const char *symname);
    #else
    void *_pam_dlopen (const char *mod_path);
    servicefn _pam_dlsym (void *handle, const char *symbol);
    void _pam_dlclose (void *handle);
    const char *_pam_dlerror (void);
    #endif
    
    /* For now we just use a stack and linear search for module data. */
    /* If it becomes apparent that there is a lot of data, it should */
    /* changed to either a sorted list or a hash table. */
    
    struct pam_data {
         char *name;
         void *data;
         void (*cleanup)(pam_handle_t *pamh, void *data, int error_status);
         struct pam_data *next;
    };
    
    void _pam_free_data(pam_handle_t *pamh, int status);
    
    char *_pam_StrTok(char *from, const char *format, char **next);
    
    char *_pam_strdup(const char *s);
    
    char *_pam_memdup(const char *s, int len);
    
    int _pam_mkargv(char *s, char ***argv, int *argc);
    
    void _pam_sanitize(pam_handle_t *pamh);
    
    void _pam_set_default_control(int *control_array, int default_action);
    
    void _pam_parse_control(int *control_array, char *tok);
    
    #define _PAM_SYSTEM_LOG_PREFIX "PAM"
    
    /* * XXX - Take care with this. It could confuse the logic of a trailing * else */
    
    #define IF_NO_PAMH(X,pamh,ERR) \
    if ((pamh) == NULL) {                             \
        syslog(LOG_ERR, _PAM_SYSTEM_LOG_PREFIX " " X ": NULL pam handle passed"); \
        return ERR;                                   \
    }
    
    /* * include some helpful macros */
    
    #include <security/_pam_macros.h>
    
    /* used to work out where control currently resides (in an application or in a module) */
    
    #define _PAM_CALLED_FROM_MODULE 1
    #define _PAM_CALLED_FROM_APP 2
    
    #define __PAM_FROM_MODULE(pamh) ((pamh)->caller_is == _PAM_CALLED_FROM_MODULE)
    #define __PAM_FROM_APP(pamh) ((pamh)->caller_is == _PAM_CALLED_FROM_APP)
    #define __PAM_TO_MODULE(pamh) \
            do { (pamh)->caller_is = _PAM_CALLED_FROM_MODULE; } while (0)
    #define __PAM_TO_APP(pamh) \
            do { (pamh)->caller_is = _PAM_CALLED_FROM_APP; } while (0)
    
    #ifdef HAVE_LIBAUDIT
    extern int _pam_auditlog(pam_handle_t *pamh, int action, int retval, int flags);
    extern int _pam_audit_end(pam_handle_t *pamh, int pam_status);
    #endif
    
    
    #endif /* _PAM_PRIVATE_H_ */

编写验证模块`pam_test_auth.c`：

#include "pam_private.h"
    #include <string.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <stdio.h>
    #include <syslog.h>
    #include <crypt.h>
    #include <shadow.h>
    #include <pwd.h>
    #include <security/pam_modules.h>
    
    #define MAXSIZE 128
    
    PAM_EXTERN int pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **argv ) {
        int i,j,count,lower_letter,upper_letter,digit;
        char *user_name, passwd[MAXSIZE], *my_crypt_passwd, salt[MAXSIZE];
        struct spwd *my_spwd;
        struct passwd *my_passwd;
    
        //get user name with pam_get_item function
        pam_get_item(pamh, PAM_USER, (const void **)&user_name);
    
        count = 0;
        do{
            // 输入超过三次退出
            if(count >= 3) {
                printf("[ERROR] Try over 3 times!\n");
                return PAM_ABORT;
            }
    
            // 输入密码
            printf("Passwd: ");
            scanf("%s", passwd);
            count++;
    
            // 打印用户名和密码
            printf("---Your Input---\n");
            printf("UserName: %s\n", user_name);
            printf("Password: %s\n", passwd);
    
            // 判断用户是否存在
            my_passwd = getpwnam(user_name);
            if (my_passwd == NULL) {
                printf("[ERROR] User not exist!\n");
                return PAM_ABORT;
            }
    
            // 密码长度不符合要求
            if (strlen(passwd) < 8) {
                printf("[ERROR] Your password length < 8\n");
                continue;
            }
    
            // 密码强度不符合要求
            lower_letter = upper_letter = digit = 0;
            for(i=0; i < strlen(passwd); i++) {
                if (passwd[i] >= 'a' && passwd[i] <= 'z')
                    lower_letter++;
                else if (passwd[i] >= 'A' && passwd[i] <= 'Z')
                    upper_letter++;
                else if (passwd[i] >= '0' && passwd[i] <= '9')
                    digit++;
            }
            if (!lower_letter || !upper_letter || !digit) {
                printf("[ERROR] Your passwd must contains lower_letter,upper_letter and digit\n");
                continue;
            }
    
            //从/etc/shadow文件中取出密码信息
            my_spwd = getspnam(user_name);
    
            //得到加密salt
            for (i=0,j=0;i<strlen(my_spwd->sp_pwdp);i++) {
                if(my_spwd->sp_pwdp[i] == '$') {
                    j++;
                    if(j == 3)
                        break;
                }
                salt[i] = my_spwd->sp_pwdp[i];
            }
            salt[i] = '\0';
    
            //计算出用户输入密码+salt后的密码
            my_crypt_passwd = crypt(passwd, salt);
    
            //比较密码是正确
            if(strcmp(my_spwd->sp_pwdp, my_crypt_passwd) == 0) {
                printf("Verify Success!\n");
                break;
            } else {
                printf("Verify Error!\n");
                return PAM_ABORT;
            }
        }while(1);
    
        //check the passwd
    
        return PAM_SUCCESS;
    }
    
        PAM_EXTERN int
    pam_sm_setcred (pam_handle_t *pamh, int flags ,int argc , const char **argv) {
        int retval;
        retval = PAM_SUCCESS;
        return retval;
    }
    
    #ifdef PAM_STATIC
    struct pam_module _pam_unix_auth_modstruct = {
        "pam_unix_auth",
        pam_sm_authenticate,
        pam_sm_setcred,
        NULL,
        NULL,
        NULL,
        NULL
    };
    #endif

生成动态库：

> gcc -o pam\_test\_auth.so -shared -fPIC pam\_test\_auth.c -lpam -lcrypt

将其放到`/lib/x86_64-linux-gnu/security`中：

> sudo mv pam\_test\_auth.so /lib/x86\_64-linux-gnu/security

因为这里我们只编写登陆验证，因此去掉账户有效性的验证，修改test.c代码如下：

#include <stdio.h>
    #include <stdlib.h>
    #include <security/pam_appl.h>
    #include <security/pam_misc.h>
    #include <security/pam_modules.h>
    
    #define MAXSIZE 128
    #define SERVICE_NAME "my_pam"
    
    int main(void) {
        int res;
        char user_name[MAXSIZE];
        pam_handle_t *handle;
        static struct pam_conv conv = {
            misc_conv,
            NULL
        };
    
        printf("UserName: ");
        scanf("%s", user_name); 
    
        res = pam_start(SERVICE_NAME, user_name, &conv, &handle);
        if (res == PAM_SUCCESS)
            puts("pam service start!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        res = pam_authenticate(handle, 0);
        if (res == PAM_SUCCESS)
            puts("passwd authenticate success!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        res = pam_end(handle, res);
        if (res == PAM_SUCCESS)
            puts("pam service end!");
        else
            printf("%s\n",pam_strerror(handle, res));
    
        return 0;
    }

重新编译`test.c`：

> gcc test.c -lpam -lpam\_misc -ldl -o test

别忘了`/etc/pam.d`中的服务配置信息还要修改为我们自己写的动态库：

wxs@ubuntu:~/my_pam$ sudo cat /etc/pam.d/my_pam 
    auth required /lib/x86_64-linux-gnu/security/pam_test_auth.so
    account required /lib/x86_64-linux-gnu/security/pam_test_auth.so

一切就绪，我们准备一个账号来测试：

用户名：mdzz
    密码：mdzzMDZZ123

此时运行程序：

因为我们代码逻辑是先判断密码强度再验证正确（这个逻辑并不正确，只是为了演示使用），因此当密码强度不够时：

![运行结果2][2]

当尝试次数超过三次时：

![运行结果3][3]

正确输入时：

![运行结果4][4]

[PAM]: /images/20220604/99da6ff11c18495fafd8dcbdf1444795.png
[PAM 1]: /images/20220604/8726ab49d08a455cbf6909ffc5c70f0d.png
[pam.d]: /images/20220604/1cf231fd6a294cb9830a19ba3f5d87a6.png
[PAM 2]: /images/20220604/4135b399601a490f930e478e18faadfe.png
[1]: /images/20220604/9b7182f5a97e48b4aab25c2c4bb4b327.png
[2]: /images/20220604/178a9980e93b43e7a19d75b4a9653fa6.png
[3]: /images/20220604/d26f10d6eeab42f8bd804ff2af31a5e7.png
[4]: /images/20220604/ba8c157dc4c54745814345a8d4d8f496.png