c - 跳过指纹读取器 PAM 模块以从 C 应用程序使用 PAM 进行身份验证

Question

我想使用 PAM 对我的 C 网络应用程序的用户进行身份验证，并且我找到了一个 a nice PAM example在 Stack 上，我附在底部。问题是，在我的开发机器中，我有一个 PAM 设置使用的指纹读取器，如 /etc/pam.d/common-auth 中所示:

#%PAM-1.0                                                                                                                                                                                                                        
#                                                                                                                                                                                                                                
# This file is autogenerated by pam-config. All changes                                                                                                                                                                          
# will be overwritten.                                                                                                                                                                                                           
#                                                                                                                                                                                                                                
# Authentication-related modules common to all services                                                                                                                                                                          
#                                                                                                                                                                                                                                
# This file is included from other service-specific PAM config files,                                                                                                                                                            
# and should contain a list of the authentication modules that define                                                                                                                                                            
# the central authentication scheme for use on the system                                                                                                                                                                        
# (e.g., /etc/shadow, LDAP, Kerberos, etc.). The default is to use the                                                                                                                                                           
# traditional Unix authentication mechanisms.                                                                                                                                                                                    
#                                                                                                                                                                                                                                
auth    required    pam_env.so                                                                                                                                                                                                 
auth    sufficient  pam_fprint.so                                                                                                                                                                                             
auth    optional    pam_gnome_keyring.so                                                                                                                                                                                         
auth    required    pam_unix2.so

pam_fprint.so 是指纹读取器插件。当您正常登录时，扫描可能会失败并提示您输入密码。但是，sshd 守护进程根本不启动指纹，我想了解它是如何跳过它的，因为例如 /etc/pam.d/sshd 引用了 common-auth 模块，所以它必须拉它..

#%PAM-1.0
auth     requisite  pam_nologin.so
auth     include        common-auth
account  requisite      pam_nologin.so
account  include        common-account
password include        common-password
session  required   pam_loginuid.so
session  include        common-session
session  optional       pam_lastlog.so   silent noupdate showfailed

我已尝试从 C 程序中引用“sshd”方案，但它仍会启动指纹读取器。我想以某种方式在 C 中跳过指纹读取器并保留我的指纹读取器默认配置。

    #include <stdlib.h>
    #include <iostream>
    #include <fstream>
    #include <security/pam_appl.h>
    #include <unistd.h>

// To build this:
// g++ test.cpp -lpam -o test

struct pam_response *reply;

//function used to get user input
int function_conversation(int num_msg, const struct pam_message **msg, struct pam_response **resp, void *appdata_ptr)
{
  *resp = reply;
  return PAM_SUCCESS;
}

int main(int argc, char** argv)
{
  if(argc != 2) {
      fprintf(stderr, "Usage: check_user <username>\n");
      exit(1);
  }
  const char *username;
  username = argv[1];

  const struct pam_conv local_conversation = { function_conversation, NULL };
  pam_handle_t *local_auth_handle = NULL; // this gets set by pam_start

  int retval;

  // local_auth_handle gets set based on the service
  retval = pam_start("common-auth", username, &local_conversation, &local_auth_handle);

  if (retval != PAM_SUCCESS)
  {
    std::cout << "pam_start returned " << retval << std::endl;
    exit(retval);
  }

  reply = (struct pam_response *)malloc(sizeof(struct pam_response));

  // *** Get the password by any method, or maybe it was passed into this function.
  reply[0].resp = getpass("Password: ");
  reply[0].resp_retcode = 0;

  retval = pam_authenticate(local_auth_handle, 0);

  if (retval != PAM_SUCCESS)
  {
    if (retval == PAM_AUTH_ERR)
    {
      std::cout << "Authentication failure." << std::endl;
    }
    else
    {
      std::cout << "pam_authenticate returned " << retval << std::endl;
    }
    exit(retval);
  }

  std::cout << "Authenticated." << std::endl;

  retval = pam_end(local_auth_handle, retval);

  if (retval != PAM_SUCCESS)
  {
    std::cout << "pam_end returned " << retval << std::endl;
    exit(retval);
  }

  return retval;
}

Answer 1

我怀疑 sshd 是否真的跳过了那个模块。相反，我怀疑指纹识别器身份验证模块(明智地)正在检查身份验证用户是在本地系统上还是通过网络(它可以从 rhost 等 PAM 数据中找出来) ) 如果这是网络身份验证，则只是默默地不执行任何操作。您可以尝试查看源代码，看看它是否有这样的测试，或者尝试通过 pam_set_item 设置 PAM_RHOST，看看是否会改变行为。

为了回答您的实际问题，我认为除了一个模块之外，没有办法告诉 PAM 运行特定的 PAM 组。做你想做的事情的预期方法是在 /etc/pam.d 中创建一个新的配置文件，该文件与你传递给 pam_start 的应用程序名称匹配em>不包含common-auth，而是只包含您要运行的模块。