/*
* $Id$
*
* Copyright (c) 1999 Andrew G. Morgan <morgan@linux.kernel.org>
*/
/*
* WARNING: AS WRITTEN THIS CODE IS NOT SECURE. THE MD5 IMPLEMENTATION
* NEEDS TO BE INTEGRATED MORE NATIVELY.
*/
#include <fcntl.h>
#include <pwd.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <security/pam_modules.h>
#include <security/pam_client.h>
#include <security/_pam_macros.h>
/*
* This is a sample module that demonstrates the use of binary prompts
* and how they can be used to implement sophisticated authentication
* schemes.
*/
struct ps_state_s {
int retval; /* last retval returned by the authentication fn */
int state; /* what state the module was in when it
returned incomplete */
char *username; /* the name of the local user */
char server_cookie[33]; /* storage for 32 bytes of server cookie */
char client_cookie[33]; /* storage for 32 bytes of client cookie */
char *secret_data; /* pointer to <NUL> terminated secret_data */
int invalid_secret; /* indication of whether the secret is valid */
pamc_bp_t current_prompt; /* place to store the current prompt */
pamc_bp_t current_reply; /* place to receive the reply prompt */
};
#define PS_STATE_ID "PAM_SECRET__STATE"
#define PS_AGENT_ID "secret@here"
#define PS_STATE_DEAD 0
#define PS_STATE_INIT 1
#define PS_STATE_PROMPT1 2
#define PS_STATE_PROMPT2 3
#define MAX_LEN_HOSTNAME 512
#define MAX_FILE_LINE_LEN 1024
/*
* Routine for generating 16*8 bits of random data represented in ASCII hex
*/
static int generate_cookie(unsigned char *buffer_33)
{
static const char hexarray[] = "0123456789abcdef";
int i, fd;
/* fill buffer_33 with 32 hex characters (lower case) + '\0' */
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0) {
D(("failed to open /dev/urandom"));
return 0;
}
read(fd, buffer_33 + 16, 16);
close(fd);
/* expand top 16 bytes into 32 nibbles */
for (i=0; i<16; ++i) {
buffer_33[2*i ] = hexarray[(buffer_33[16+i] & 0xf0)>>4];
buffer_33[2*i+1] = hexarray[(buffer_33[16+i] & 0x0f)];
}
buffer_33[32] = '\0';
return 1;
}
/*
* XXX - This is a hack, and is fundamentally insecure. Its subject to
* all sorts of attacks not to mention the fact that all our secrets
* will be displayed on the command line for someone doing 'ps' to
* see. This is just for programming convenience in this instance, it
* needs to be replaced with the md5 code. Although I am loath to
* add yet another instance of md5 code to the Linux-PAM source code.
* [Need to think of a cleaner way to do this for the distribution as
* a whole...]
*/
#define COMMAND_FORMAT "/bin/echo -n '%s|%s|%s'|/usr/bin/md5sum -"
int create_digest(const char *d1, const char *d2, const char *d3,
char *buffer_33)
{
int length;
char *buffer;
FILE *pipe;
length = strlen(d1)+strlen(d2)+strlen(d3)+sizeof(COMMAND_FORMAT);
buffer = malloc(length);
if (buffer == NULL) {
D(("out of memory"));
return 0;
}
sprintf(buffer, COMMAND_FORMAT, d1,d2,d3);
D(("executing pipe [%s]", buffer));
pipe = popen(buffer, "r");
memset(buffer, 0, length);
free(buffer);
if (pipe == NULL) {
D(("failed to launch pipe"));
return 0;
}
if (fgets(buffer_33, 33, pipe) == NULL) {
D(("failed to read digest"));
return 0;
}
if (strlen(buffer_33) != 32) {
D(("digest was not 32 chars"));
return 0;
}
fclose(pipe);
D(("done [%s]", buffer_33));
return 1;
}
/*
* method to attempt to instruct the application's conversation function
*/
static int converse(pam_handle_t *pamh, struct ps_state_s *new)
{
int retval;
struct pam_conv *conv;
D(("called"));
retval = pam_get_item(pamh, PAM_CONV, (const void **) &conv);
if (retval == PAM_SUCCESS) {
struct pam_message msg;
struct pam_response *single_reply;
const struct pam_message *msg_ptr;
memset(&msg, 0, sizeof(msg));
msg.msg_style = PAM_BINARY_PROMPT;
msg.msg = (const char *) new->current_prompt;
msg_ptr = &msg;
single_reply = NULL;
retval = conv->conv(1, &msg_ptr, &single_reply, conv->appdata_ptr);
if (retval == PAM_SUCCESS) {
if ((single_reply == NULL) || (single_reply->resp == NULL)) {
retval == PAM_CONV_ERR;
} else {
new->current_reply = (pamc_bp_t) single_reply->resp;
single_reply->resp = NULL;
}
}
if (single_reply) {
free(single_reply);
}
}
#ifdef PAM_DEBUG
if (retval == PAM_SUCCESS) {
D(("reply has length=%d and control=%u",
PAM_BP_LENGTH(new->current_reply),
PAM_BP_CONTROL(new->current_reply)));
}
D(("returning %s", pam_strerror(pamh, retval)));
#endif
return retval;
}
/*
* identify the secret in question
*/
#define SECRET_FILE_FORMAT "%s/.secret@here"
char *identify_secret(char *identity, const char *user)
{
struct passwd *pwd;
char *temp;
FILE *secrets;
int length_id;
pwd = getpwnam(user);
if ((pwd == NULL) || (pwd->pw_dir == NULL)) {
D(("user [%s] is not known", user));
return NULL;
}
length_id = strlen(pwd->pw_dir) + sizeof(SECRET_FILE_FORMAT);
temp = malloc(length_id);
if (temp == NULL) {
D(("out of memory"));
pwd = NULL;
return NULL;
}
sprintf(temp, SECRET_FILE_FORMAT, pwd->pw_dir);
pwd = NULL;
D(("opening key file [%s]", temp));
secrets = fopen(temp, "r");
memset(temp, 0, length_id);
if (secrets == NULL) {
D(("failed to open key file"));
return NULL;
}
length_id = strlen(identity);
temp = malloc(MAX_FILE_LINE_LEN);
for (;;) {
char *secret = NULL;
if (fgets(temp, MAX_FILE_LINE_LEN, secrets) == NULL) {
fclose(secrets);
return NULL;
}
D(("cf[%s][%s]", identity, temp));
if (memcmp(temp, identity, length_id)) {
continue;
}
D(("found entry"));
fclose(secrets);
for (secret=temp+length_id; *secret; ++secret) {
if (!(*secret == ' ' || *secret == '\n' || *secret == '\t')) {
break;
}
}
memmove(temp, secret, MAX_FILE_LINE_LEN-(secret-(temp+length_id)));
secret = temp;
for (; *secret; ++secret) {
if (*secret == ' ' || *secret == '\n' || *secret == '\t') {
break;
}
}
if (*secret) {
*secret = '\0';
}
D(("secret found [%s]", temp));
return temp;
}
/* NOT REACHED */
}
/*
* function to perform the two message authentication process
* (with support for event driven conversation functions)
*/
static int auth_sequence(pam_handle_t *pamh,
const struct ps_state_s *old, struct ps_state_s *new)
{
const char *rhostname;
const char *rusername;
int retval;
retval = pam_get_item(pamh, PAM_RUSER, (const void **) &rusername);
if ((retval != PAM_SUCCESS) || (rusername == NULL)) {
D(("failed to obtain an rusername"));
new->state = PS_STATE_DEAD;
return PAM_AUTH_ERR;
}
retval = pam_get_item(pamh, PAM_RHOST, (const void **) &rhostname);
if ((retval != PAM_SUCCESS) || (rhostname == NULL)) {
D(("failed to identify local hostname: ", pam_strerror(pamh, retval)));
new->state = PS_STATE_DEAD;
return PAM_AUTH_ERR;
}
D(("switch on new->state=%d [%s@%s]", new->state, rusername, rhostname));
switch (new->state) {
case PS_STATE_INIT:
{
const char *user = NULL;
retval = pam_get_user(pamh, &user, NULL);
if ((retval == PAM_SUCCESS) && (user == NULL)) {
D(("success but no username?"));
new->state = PS_STATE_DEAD;
retval = PAM_USER_UNKNOWN;
}
if (retval != PAM_SUCCESS) {
if (retval == PAM_CONV_AGAIN) {
retval = PAM_INCOMPLETE;
} else {
new->state = PS_STATE_DEAD;
}
D(("state init failed: %s", pam_strerror(pamh, retval)));
return retval;
}
/* nothing else in this 'case' can be retried */
new->username = strdup(user);
if (new->username == NULL) {
D(("out of memory"));
new->state = PS_STATE_DEAD;
return PAM_BUF_ERR;
}
if (! generate_cookie(new->server_cookie)) {
D(("problem generating server cookie"));
new->state = PS_STATE_DEAD;
return PAM_ABORT;
}
new->current_prompt = NULL;
PAM_BP_RENEW(&new->current_prompt, PAM_BPC_SELECT,
sizeof(PS_AGENT_ID) + strlen(rusername) + 1
+ strlen(rhostname) + 1 + 32);
sprintf(PAM_BP_WDATA(new->current_prompt),
PS_AGENT_ID "/%s@%s|%.32s", rusername, rhostname,
new->server_cookie);
/* note, the BP is guaranteed by the spec to be <NUL> terminated */
D(("initialization packet [%s]", PAM_BP_DATA(new->current_prompt)));
/* fall through */
new->state = PS_STATE_PROMPT1;
D(("fall through to state_prompt1"));
}
case PS_STATE_PROMPT1:
{
int i, length;
/* send {secret@here/jdoe@client.host|<s_cookie>} */
retval = converse(pamh, new);
if (retval != PAM_SUCCESS) {
if (retval == PAM_CONV_AGAIN) {
D(("conversation failed to complete"));
return PAM_INCOMPLETE;
} else {
new->state = PS_STATE_DEAD;
return retval;
}
}
if (retval != PAM_SUCCESS) {
D(("failed to read ruser@rhost"));
new->state = PS_STATE_DEAD;
return PAM_AUTH_ERR;
}
/* expect to receive the following {<seqid>|<a_cookie>} */
if (new->current_reply == NULL) {
D(("converstation returned [%s] but gave no reply",
pam_strerror(pamh, retval)));
new->state = PS_STATE_DEAD;
return PAM_CONV_ERR;
}
/* find | */
length = PAM_BP_LENGTH(new->current_reply);
for (i=0; i<length; ++i) {
if (PAM_BP_RDATA(new->current_reply)[i] == '|') {
break;
}
}
if (i >= length) {
D(("malformed response (no |) of length %d", length));
new->state = PS_STATE_DEAD;
return PAM_CONV_ERR;
}
if ((length - ++i) != 32) {
D(("cookie is incorrect length (%d,%d) %d != 32",
length, i, length-i));
new->state = PS_STATE_DEAD;
return PAM_CONV_ERR;
}
/* copy client cookie */
memcpy(new->client_cookie, PAM_BP_RDATA(new->current_reply)+i, 32);
/* generate a prompt that is length(seqid) + length(|) + 32 long */
PAM_BP_RENEW(&new->current_prompt, PAM_BPC_OK, i+32);
/* copy the head of the response prompt */
memcpy(PAM_BP_WDATA(new->current_prompt),
PAM_BP_RDATA(new->current_reply), i);
PAM_BP_RENEW(&new->current_reply, 0, 0);
/* look up the secret */
new->invalid_secret = 0;
if (new->secret_data == NULL) {
char *ruser_rhost;
ruser_rhost = malloc(strlen(rusername)+2+strlen(rhostname));
if (ruser_rhost == NULL) {
D(("out of memory"));
new->state = PS_STATE_DEAD;
return PAM_BUF_ERR;
}
sprintf(ruser_rhost, "%s@%s", rusername, rhostname);
new->secret_data = identify_secret(ruser_rhost, new->username);
memset(ruser_rhost, 0, strlen(ruser_rhost));
free(ruser_rhost);
}
if (new->secret_data == NULL) {
D(("secret not found for user"));
new->invalid_secret = 1;
/* need to make up a secret */
new->secret_data = malloc(32 + 1);
if (new->secret_data == NULL) {
D(("out of memory"));
new->state = PS_STATE_DEAD;
return PAM_BUF_ERR;
}
if (! generate_cookie(new->secret_data)) {
D(("what's up - no fake cookie generated?"));
new->state = PS_STATE_DEAD;
return PAM_ABORT;
}
}
/* construct md5[<client_cookie>|<server_cookie>|<secret_data>] */
if (! create_digest(new->client_cookie, new->server_cookie,
new->secret_data,
PAM_BP_WDATA(new->current_prompt)+i)) {
D(("md5 digesting failed"));
new->state = PS_STATE_DEAD;
return PAM_ABORT;
}
/* prompt2 is now constructed - fall through to send it */
}
case PS_STATE_PROMPT2:
{
/* send {<seqid>|md5[<client_cookie>|<server_cookie>|<secret_data>]} */
retval = converse(pamh, new);
if (retval != PAM_SUCCESS) {
if (retval == PAM_CONV_AGAIN) {
D(("conversation failed to complete"));
return PAM_INCOMPLETE;
} else {
new->state = PS_STATE_DEAD;
return retval;
}
}
/* After we complete this section, we should not be able to
recall this authentication function. So, we force all
future calls into the weeds. */
new->state = PS_STATE_DEAD;
/* expect reply:{md5[<secret_data>|<server_cookie>|<client_cookie>]} */
{
int cf;
char expectation[33];
if (!create_digest(new->secret_data, new->server_cookie,
new->client_cookie, expectation)) {
new->state = PS_STATE_DEAD;
return PAM_ABORT;
}
cf = strcmp(expectation, PAM_BP_RDATA(new->current_reply));
memset(expectation, 0, sizeof(expectation));
if (cf || new->invalid_secret) {
D(("failed to authenticate"));
return PAM_AUTH_ERR;
}
}
D(("correctly authenticated :)"));
return PAM_SUCCESS;
}
default:
new->state = PS_STATE_DEAD;
case PS_STATE_DEAD:
D(("state is currently dead/unknown"));
return PAM_AUTH_ERR;
}
fprintf(stderr, "pam_secret: this should not be reached\n");
return PAM_ABORT;
}
static void clean_data(pam_handle_t *pamh, void *datum, int error_status)
{
struct ps_state_s *data = datum;
D(("liberating datum=%p", datum));
if (data) {
D(("renew prompt"));
PAM_BP_RENEW(&data->current_prompt, 0, 0);
D(("renew reply"));
PAM_BP_RENEW(&data->current_reply, 0, 0);
D(("overwrite datum"));
memset(data, 0, sizeof(struct ps_state_s));
D(("liberate datum"));
free(data);
}
D(("done."));
}
/*
* front end for the authentication function
*/
int pam_sm_authenticate(pam_handle_t *pamh, int flags,
int argc, const char **argv)
{
int retval;
struct ps_state_s *new_data;
const struct ps_state_s *old_data;
D(("called"));
new_data = calloc(1, sizeof(struct ps_state_s));
if (new_data == NULL) {
D(("out of memory"));
return PAM_BUF_ERR;
}
new_data->retval = PAM_SUCCESS;
retval = pam_get_data(pamh, PS_STATE_ID, (const void **) &old_data);
if (retval == PAM_SUCCESS) {
new_data->state = old_data->state;
memcpy(new_data->server_cookie, old_data->server_cookie, 32);
memcpy(new_data->client_cookie, old_data->client_cookie, 32);
if (old_data->username) {
new_data->username = strdup(old_data->username);
}
if (old_data->secret_data) {
new_data->secret_data = strdup(old_data->secret_data);
}
if (old_data->current_prompt) {
int length;
length = PAM_BP_LENGTH(old_data->current_prompt);
PAM_BP_RENEW(&new_data->current_prompt,
PAM_BP_CONTROL(old_data->current_prompt), length);
PAM_BP_FILL(new_data->current_prompt, 0, length,
PAM_BP_RDATA(old_data->current_prompt));
}
/* don't need to duplicate current_reply */
} else {
old_data = NULL;
new_data->state = PS_STATE_INIT;
}
D(("call auth_sequence"));
new_data->retval = auth_sequence(pamh, old_data, new_data);
D(("returned from auth_sequence"));
retval = pam_set_data(pamh, PS_STATE_ID, new_data, clean_data);
if (retval != PAM_SUCCESS) {
D(("unable to store new_data"));
} else {
retval = new_data->retval;
}
old_data = new_data = NULL;
D(("done (%d)", retval));
return retval;
}
/*
* front end for the credential setting function
*/
#define AUTH_SESSION_TICKET_ENV_FORMAT "AUTH_SESSION_TICKET="
int pam_sm_setcred(pam_handle_t *pamh, int flags,
int argc, const char **argv)
{
int retval;
const struct ps_state_s *old_data;
D(("called"));
/* XXX - need to pay attention to the various flavors of call */
/* XXX - need provide an option to turn this feature on/off: if
other modules want to supply an AUTH_SESSION_TICKET, we should
leave it up to the admin which module dominiates. */
retval = pam_get_data(pamh, PS_STATE_ID, (const void **) &old_data);
if (retval != PAM_SUCCESS) {
D(("no data to base decision on"));
return PAM_AUTH_ERR;
}
/*
* If ok, export a derived shared secret session ticket to the
* client's PAM environment - the ticket has the form
*
* AUTH_SESSION_TICKET =
* md5[<server_cookie>|<secret_data>|<client_cookie>]
*
* This is a precursor to supporting a spoof resistant trusted
* path mechanism. This shared secret ticket can be used to add
* a hard-to-guess checksum to further authentication data.
*/
retval = old_data->retval;
if (retval == PAM_SUCCESS) {
char envticket[sizeof(AUTH_SESSION_TICKET_ENV_FORMAT)+32];
memcpy(envticket, AUTH_SESSION_TICKET_ENV_FORMAT,
sizeof(AUTH_SESSION_TICKET_ENV_FORMAT));
if (! create_digest(old_data->server_cookie, old_data->secret_data,
old_data->client_cookie,
envticket+sizeof(AUTH_SESSION_TICKET_ENV_FORMAT)-1
)) {
D(("unable to generate a digest for session ticket"));
return PAM_ABORT;
}
D(("putenv[%s]", envticket));
retval = pam_putenv(pamh, envticket);
memset(envticket, 0, sizeof(envticket));
}
old_data = NULL;
D(("done (%d)", retval));
return retval;
}