pam_conv(3) [osx man page]
PAM_CONV(3) BSD Library Functions Manual PAM_CONV(3) NAME
pam_conv -- PAM conversation system LIBRARY
Pluggable Authentication Module Library (libpam, -lpam) SYNOPSIS
#include <security/pam_appl.h> struct pam_message { int msg_style; char *msg; }; struct pam_response { char *resp; int resp_retcode; }; struct pam_conv { int (*conv)(int, const struct pam_message **, struct pam_response **, void *); void *appdata_ptr; }; DESCRIPTION
The PAM library uses an application-defined callback to communicate with the user. This callback is specified by the struct pam_conv passed to pam_start() at the start of the transaction. It is also possible to set or change the conversation function at any point during a PAM transaction by changing the value of the PAM_CONV item. The conversation function's first argument specifies the number of messages (up to PAM_NUM_MSG) to process. The second argument is a pointer to an array of pointers to pam_message structures containing the actual messages. Each message can have one of four types, specified by the msg_style member of struct pam_message: PAM_PROMPT_ECHO_OFF Display a prompt and accept the user's response without echoing it to the terminal. This is commonly used for passwords. PAM_PROMPT_ECHO_ON Display a prompt and accept the user's response, echoing it to the terminal. This is commonly used for login names and one-time passphrases. PAM_ERROR_MSG Display an error message. PAM_TEXT_INFO Display an informational message. In each case, the prompt or message to display is pointed to by the msg member of struct pam_message. It can be up to PAM_MAX_MSG_SIZE char- acters long, including the terminating NUL. On success, the conversation function should allocate and fill a contiguous array of struct pam_response, one for each message that was passed in. A pointer to the user's response to each message (or NULL in the case of informational or error messages) should be stored in the resp member of the corresponding struct pam_response. Each response can be up to PAM_MAX_RESP_SIZE characters long, including the terminat- ing NUL. The resp_retcode member of struct pam_response is unused and should be set to zero. The conversation function should store a pointer to this array in the location pointed to by its third argument. It is the caller's respon- sibility to release both this array and the responses themselves, using free(3). It is the conversation function's responsibility to ensure that it is legal to do so. The appdata_ptr member of struct pam_conv is passed unmodified to the conversation function as its fourth and final argument. On failure, the conversation function should release any resources it has allocated, and return one of the predefined PAM error codes. RETURN VALUES
The conversation function should return one of the following values: [PAM_BUF_ERR] Memory buffer error. [PAM_CONV_ERR] Conversation failure. [PAM_SUCCESS] Success. [PAM_SYSTEM_ERR] System error. SEE ALSO
openpam_nullconv(3), openpam_ttyconv(3), pam(3), pam_error(3), pam_get_item(3), pam_info(3), pam_prompt(3), pam_set_item(3), pam_start(3) STANDARDS
X/Open Single Sign-On Service (XSSO) - Pluggable Authentication Modules, June 1997. AUTHORS
The OpenPAM library and this manual page were developed for the FreeBSD Project by ThinkSec AS and Network Associates Laboratories, the Secu- rity Research Division of Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 (``CBOSS''), as part of the DARPA CHATS research program. BSD
June 16, 2005 BSD
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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(7) Linux-PAM Manual 06/04/2011 PAM_CONV(3)