How to mock the pam_handle struct - c

Question

Background
I am developing a module using the PAM specification and I would like to test one of the pam functions (specifically pam_sm_authenticate) to make sure that the helper functions that I have implement play nice with the specification.
The pam_sm_[authenticate, acct_mgmt...etc.] series functions all take the same parameters.
int pam_sm_acct_mgmt(pam_handle_t *pamh, int flags, int argc, const char **argv)
I am having trouble mocking struct pam_handle, but need to as this structure will contain information vital to authenticating users.
Using PAM header information from the internet (pam_appl.h and pam_private.h) I have attempted to use the structure directly as pam_handle_t normalPamh; and populate it myself, but when I try to I get the following error:
error: aggregate 'pam_handle_t normalPamh' has incomplete type and cannot be defined
I would really like to test my module to make sure that I haven't done anything that will cause segmentation faults and that I'm using memory within reasonable limits, but I am having trouble doing so because I can't mock this structure.
Question
How do I mock the pam_handle_t struct?

Answer 1

It sounds like, the headers you're referring to declare the pam-handle type along the lines of:
typedef struct pam_handle pam_handle_t;
However the actual definition of the struct pam_handle is NOT part of the headers you describe. To mock it, you would need to specify the actual structure before writing any code that code accessing the struct pam_handle members (whatever they are). I.E:
In your interface definitions, you "post-pone" the structure definition, by using handle only:
int pam_sm_acct_mgmt(pam_handle_t *pamh, int flags, int argc, const char **argv);
In your test code, where you modify handle-members for testing purposes, you have to define it, e.g.
#include "interface_to_be_tested.h"
// declare the pam_handle
struct pam_handle
{
// provide definition of struct-members here
};
...
// Test code here
Update: The structure seems to be defined in libpam/pam_private.h, so including that file in your test-code ought to be sufficient. Note the header is "private", so your actual implementation should of course NOT use this.
Hope that helps!

Answer 2

I found some open source software that does exactly what I need it to.
It's called pamtester and it compiles on a number of *nix systems.
Once it's installed you can run it like:
pamtester -v -I user=test01#test.com -I rhost=192.168.2.150 dovecot test01#test.com "authenticate(PAM_ESTABLISH_CRED)"
It will take care of everything else that is needed to establish user credentials.
I wanted to use it in automated testing through C, so I wrapped a lot of the calls in a bash script where I could specify input I wanted to change like user and ruser.
The problem is passwords need to be entered when the program asks for it. I solved this using popen in my C source.
Here is an example of what I did for reference. It's not perfect, but for anyone else that might run into a similar situation this might serve as a starting point.
int testPamSmAuthenticate(char * username, char * hostname, char * password) {
//--------------------------------------
// declarations
//--------------------------------------
char testCommand[512];
char passwordPromptResponse[128];
char resultLine[3];
FILE * testFile;
//--------------------------------------
// declarations
//--------------------------------------
sprintf(testCommand, "%s %s %s", PAM_TEST_SCRIPT_PATH, username, hostname);
sprintf(passwordPromptResponse, "%s\n", password);
//--------------------------------------
// run the command and enter a password
//--------------------------------------
if (!(testFile = popen(testCommand, "w"))){
return(1);
}
fputs(passwordPromptResponse, testFile);
pclose(testFile);
//--------------------------------------
// get the output of the command from
// the text file written by bash
//--------------------------------------
testFile = fopen(PAM_TEST_RESULT_PATH, "r");
while (fgets(resultLine, sizeof(resultLine), testFile)) {
printf("%s", resultLine);
}
fclose(testFile);
//--------------------------------------
// evaulate and return a code
// 1 == authentication good
// 0 == authentication bad
//--------------------------------------
if (strchr(resultLine, '0')) {
printf("Authentication successful!\n");
return(1);
}
printf("Authentication failed!\n");
return(0);
}
More information about the use of this program is available by downloading the source and reading it's README file.