misc_conv(3) [centos man page]
MISC_CONV(3) Linux-PAM Manual MISC_CONV(3) NAME
misc_conv - text based conversation function SYNOPSIS
#include <security/pam_misc.h> int misc_conv(int num_msg, const struct pam_message **msgm, struct pam_response **response, void *appdata_ptr); DESCRIPTION
The misc_conv function is part of libpam_misc and not of the standard libpam library. This function will prompt the user with the appropriate comments and obtain the appropriate inputs as directed by authentication modules. In addition to simply slotting into the appropriate pam_conv(3), this function provides some time-out facilities. The function exports five variables that can be used by an application programmer to limit the amount of time this conversation function will spend waiting for the user to type something. The five variabls are as follows: time_t pam_misc_conv_warn_time; This variable contains the time (as returned by time(2)) that the user should be first warned that the clock is ticking. By default it has the value 0, which indicates that no such warning will be given. The application may set its value to sometime in the future, but this should be done prior to passing control to the Linux-PAM library. const char *pam_misc_conv_warn_line; Used in conjuction with pam_misc_conv_warn_time, this variable is a pointer to the string that will be displayed when it becomes time to warn the user that the timeout is approaching. Its default value is a translated version of "...Time is running out...", but this can be changed by the application prior to passing control to Linux-PAM. time_t pam_misc_conv_die_time; This variable contains the time (as returned by time(2)) that the will time out. By default it has the value 0, which indicates that the conversation function will not timeout. The application may set its value to sometime in the future, but this should be done prior to passing control to the Linux-PAM library. const char *pam_misc_conv_die_line; Used in conjuction with pam_misc_conv_die_time, this variable is a pointer to the string that will be displayed when the conversation times out. Its default value is a translated version of "...Sorry, your time is up!", but this can be changed by the application prior to passing control to Linux-PAM. int pam_misc_conv_died; Following a return from the Linux-PAM libraray, the value of this variable indicates whether the conversation has timed out. A value of 1 indicates the time-out occurred. The following two function pointers are available for supporting binary prompts in the conversation function. They are optimized for the current incarnation of the libpamc library and are subject to change. int (*pam_binary_handler_fn)(void *appdata, pamc_bp_t *prompt_p); This function pointer is initialized to NULL but can be filled with a function that provides machine-machine (hidden) message exchange. It is intended for use with hidden authentication protocols such as RSA or Diffie-Hellman key exchanges. (This is still under development.) int (*pam_binary_handler_free)(void *appdata, pamc_bp_t *delete_me); This function pointer is initialized to PAM_BP_RENEW(delete_me, 0, 0), but can be redefined as desired by the application. SEE ALSO
pam_conv(3), pam(8) STANDARDS
The misc_conv function is part of the libpam_misc Library and not defined in any standard. Linux-PAM Manual 09/19/2013 MISC_CONV(3)
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PAM_CONV(3) Linux-PAM Manual PAM_CONV(3) NAME
pam_conv - PAM conversation function SYNOPSIS
#include <security/pam_appl.h> struct pam_message { int msg_style; const char *msg; }; struct pam_response { char *resp; int resp_retcode; }; struct pam_conv { int (*conv)(int num_msg, const struct pam_message **msg, struct pam_response **resp, void *appdata_ptr); void *appdata_ptr; }; DESCRIPTION
The PAM library uses an application-defined callback to allow a direct communication between a loaded module and the application. This callback is specified by the struct pam_conv passed to pam_start(3) at the start of the transaction. When a module calls the referenced conv() function, the argument appdata_ptr is set to the second element of this structure. The other arguments of a call to conv() concern the information exchanged by module and application. That is to say, num_msg holds the length of the array of pointers, msg. After a successful return, the pointer resp points to an array of pam_response structures, holding the application supplied text. The resp_retcode member of this struct is unused and should be set to zero. It is the caller's responsibility to release both, this array and the responses themselves, using free(3). Note, *resp is a struct pam_response array and not an array of pointers. The number of responses is always equal to the num_msg conversation function argument. This does require that the response array is free(3)'d after every call to the conversation function. The index of the responses corresponds directly to the prompt index in the pam_message array. On failure, the conversation function should release any resources it has allocated, and return one of the predefined PAM error codes. Each message can have one of four types, specified by the msg_style member of struct pam_message: PAM_PROMPT_ECHO_OFF Obtain a string without echoing any text. PAM_PROMPT_ECHO_ON Obtain a string whilst echoing text. PAM_ERROR_MSG Display an error message. PAM_TEXT_INFO Display some text. The point of having an array of messages is that it becomes possible to pass a number of things to the application in a single call from the module. It can also be convenient for the application that related things come at once: a windows based application can then present a single form with many messages/prompts on at once. In passing, it is worth noting that there is a descrepency between the way Linux-PAM handles the const struct pam_message **msg conversation function argument from the way that Solaris' PAM (and derivitives, known to include HP/UX, are there others?) does. Linux-PAM interprets the msg argument as entirely equivalent to the following prototype const struct pam_message *msg[] (which, in spirit, is consistent with the commonly used prototypes for argv argument to the familiar main() function: char **argv; and char *argv[]). Said another way Linux-PAM interprets the msg argument as a pointer to an array of num_msg read only 'struct pam_message' pointers. Solaris' PAM implementation interprets this argument as a pointer to a pointer to an array of num_msg pam_message structures. Fortunately, perhaps, for most module/application developers when num_msg has a value of one these two definitions are entirely equivalent. Unfortunately, casually raising this number to two has led to unanticipated compatibility problems. For what its worth the two known module writer work-arounds for trying to maintain source level compatibility with both PAM implementations are: o never call the conversation function with num_msg greater than one. o set up msg as doubly referenced so both types of conversation function can find the messages. That is, make msg[n] = & (( *msg )[n]) RETURN VALUES
PAM_BUF_ERR Memory buffer error. PAM_CONV_ERR Conversation failure. The application should not set *resp. PAM_SUCCESS Success. SEE ALSO
pam_start(3), pam_set_item(3), pam_get_item(3), pam_strerror(3), pam(8) Linux-PAM Manual 04/01/2010 PAM_CONV(3)