pam_get_item() problems

[Jason Gerfen]

I am looking for assistance using the pam_get_item() function.  
According to the pam module writters guide on kernel.org I should use 
pam_get_item() as the following:

extern int pam_get_item( const pam_handle_t *pamh,
                                              int item_type,
                                              const void **item );


As you can see in the code below it should retrieve the password entered 
during login and store it in the const void **password variable.  But 
what happens is it completely crashes the display manager.  I don't get 
it, I have looked at other people's source (pam_krb5afs.c for example) 
and they are calling the pam_get_item() function in much the same way 
and yet it isn't crashing their display.  Am I missing something or over 
looking a compile option perhaps?  Any help is greatly appreciated.

configured my pam configuration as:
/etc/pam.d/xdm & /etc/pam.d/gdm (GUI login stuff for KDE & Gnome)

auth sufficient pam_test.so try_first_pass


I have compiled the following code as:

%> gcc -fPIC -o pam_test.o -c pam_test.c

%> ld --shared -x -lc -o pam_test.so pam_test.o -lpam

%> cp -m 755 pam_test.so /lib/security;


[code snip]

/* PAM includes */

#include <security/pam_modules.h>

#include <security/_pam_macros.h>

#include <security/pam_appl.h>

/* PAM definitions */

#define PAM_SM_ACCOUNT

#define PAM_SM_AUTH

#define PAM_SM_PASSWORD

#define PAM_SM_SESSION

/* Log events to syslog */

static void _pam_log(int err, const char *format, ...)

{

    va_list  args;

    va_start(args, format);

    openlog("PAM-RemoteKRB5", LOG_PID | LOG_NDELAY, LOG_SYSLOG);

    vsyslog(err, format, args);

    va_end(args);

    closelog();

}

PAM_EXTERN

int pam_sm_authenticate( pam_handle_t *pamh, int flags, int argc, const char **argv )

{

    int retval;

    udataptr myUser = &localUser;

    myConfigPtr myConfig = &localConfig;

    char user[15];

    const void ** password;

    myUser->usrname=user;

    if( ( retval = pam_get_user( pamh, &( myUser->usrname ), "pam_tester: " ) != PAM_SUCCESS ) ) {

        _pam_log( LOG_ERR, "Could not obtain username" );

        return 1;

    } else {

        _pam_log( LOG_ERR, "Obtained Username: %s", myUser->usrname );

    }

// This bit is not working?!

    if( pam_get_item( pamh, PAM_AUTHTOK, password ) != PAM_SUCCESS ) {

        _pam_log( LOG_ERR, "Error retrieving password" );

        return 1;

    } else {

        strcpy( *( &( myUser->password ) ), *password );

    }

}


Jason Gerfen wrote:

> Oops, thanks for the pointer... I will modify that.  Know anything 
> about using the pam_get_item()?
>
> Justin F. wrote:
>
>>> {
>>>    int retval;
>>>    udataptr myUser = &localUser;
>>>    myConfigPtr myConfig = &localConfig;
>>>    char user[15];
>>>    char *password;
>>>    myUser->usrname=user;
>>>    char error_msg[30];
>>>
>>>    if( ( retval = pam_get_user( pamh, &( myUser->usrname ), "PAM_test
>>> login:" ) != PAM_SUCCESS ) ) {
>>>        strcpy( error_msg, "Could not obtain user name: " );
>>>        strcat( error_msg, myUser->usrname );
>>>   
>>
>>
>> You do not feel having a fixed length array of 30b with a 28b 
>> messages and
>> strcat'ing a username into it could cause problems?
>> This leads you with like 1 byte usernames.
>>
>>
>>  
>>
>>>    if( ( retval = pam_get_user( pamh, &( myUser->usrname ), "PAM_test
>>> login:" ) == PAM_SUCCESS ) ) {
>>>        strcpy( error_msg, "Obtained username: " );
>>>        strcat( error_msg, myUser->usrname );
>>>   
>>
>>
>>
>> Same deal here, however you have more wiggle room.
>>
>>
>> However, I am not a pam expert, so I can't really answer your 
>> question- I
>> just noticed those two potential overflows.
>>
>> Justin F.
>>
>>
>>
>>  
>>
>>> -- 
>>> Jason Gerfen
>>> jason.gerfen at scl.utah.edu
>>>
>>> "And remember... If the ladies
>>> don't find you handsome, they
>>> should at least find you handy..."
>>>             ~The Red Green show
>>>
>>> _______________________________________________
>>> Pam-list mailing list
>>> Pam-list at redhat.com
>>> https://www.redhat.com/mailman/listinfo/pam-list
>>>
>>>
>>>   
>>
>>
>>
>> _______________________________________________
>> Pam-list mailing list
>> Pam-list at redhat.com
>> https://www.redhat.com/mailman/listinfo/pam-list
>>  
>>
>
>


-- 
Jason Gerfen
jason.gerfen at scl.utah.edu

"And remember... If the ladies
 don't find you handsome, they
 should at least find you handy..."
             ~The Red Green show