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/* pam_keyinit.c: Initialise the session keyring on login through a PAM module
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include "config.h"
#include <stdarg.h>
#include <string.h>
#include <syslog.h>
#include <pwd.h>
#include <unistd.h>
#include <errno.h>
#include <security/pam_modules.h>
#include <security/pam_modutil.h>
#include <security/pam_ext.h>
#include <sys/syscall.h>
#define KEY_SPEC_SESSION_KEYRING -3 /* ID for session keyring */
#define KEY_SPEC_USER_KEYRING -4 /* ID for UID-specific keyring */
#define KEY_SPEC_USER_SESSION_KEYRING -5 /* - key ID for UID-session keyring */
#define KEYCTL_GET_KEYRING_ID 0 /* ask for a keyring's ID */
#define KEYCTL_JOIN_SESSION_KEYRING 1 /* start named session keyring */
#define KEYCTL_REVOKE 3 /* revoke a key */
#define KEYCTL_LINK 8 /* link a key into a keyring */
static int my_session_keyring;
static int session_counter;
static int do_revoke;
static int xdebug = 0;
static void debug(pam_handle_t *pamh, const char *fmt, ...)
__attribute__((format(printf, 2, 3)));
static void debug(pam_handle_t *pamh, const char *fmt, ...)
{
va_list va;
if (xdebug) {
va_start(va, fmt);
pam_vsyslog(pamh, LOG_DEBUG, fmt, va);
va_end(va);
}
}
static int error(pam_handle_t *pamh, const char *fmt, ...)
__attribute__((format(printf, 2, 3)));
static int error(pam_handle_t *pamh, const char *fmt, ...)
{
va_list va;
va_start(va, fmt);
pam_vsyslog(pamh, LOG_ERR, fmt, va);
va_end(va);
return PAM_SESSION_ERR;
}
/*
* initialise the session keyring for this process
*/
static int init_keyrings(pam_handle_t *pamh, int force)
{
int session, usession, ret;
if (!force) {
/* get the IDs of the session keyring and the user session
* keyring */
session = syscall(__NR_keyctl,
KEYCTL_GET_KEYRING_ID,
KEY_SPEC_SESSION_KEYRING,
0);
debug(pamh, "GET SESSION = %d", session);
if (session < 0) {
/* don't worry about keyrings if facility not
* installed */
if (errno == ENOSYS)
return PAM_SUCCESS;
return PAM_SESSION_ERR;
}
usession = syscall(__NR_keyctl,
KEYCTL_GET_KEYRING_ID,
KEY_SPEC_USER_SESSION_KEYRING,
0);
debug(pamh, "GET SESSION = %d", usession);
if (usession < 0)
return PAM_SESSION_ERR;
/* if the user session keyring is our keyring, then we don't
* need to do anything if we're not forcing */
if (session != usession)
return PAM_SUCCESS;
}
/* create a session keyring, discarding the old one */
ret = syscall(__NR_keyctl,
KEYCTL_JOIN_SESSION_KEYRING,
NULL);
debug(pamh, "JOIN = %d", ret);
if (ret < 0)
return PAM_SESSION_ERR;
my_session_keyring = ret;
/* make a link from the session keyring to the user keyring */
ret = syscall(__NR_keyctl,
KEYCTL_LINK,
KEY_SPEC_USER_KEYRING,
KEY_SPEC_SESSION_KEYRING);
return ret < 0 ? PAM_SESSION_ERR : PAM_SUCCESS;
}
/*
* revoke the session keyring for this process
*/
static void kill_keyrings(pam_handle_t *pamh)
{
/* revoke the session keyring we created earlier */
if (my_session_keyring > 0) {
debug(pamh, "REVOKE %d", my_session_keyring);
syscall(__NR_keyctl,
KEYCTL_REVOKE,
my_session_keyring);
my_session_keyring = 0;
}
}
/*
* open a PAM session by making sure there's a session keyring
*/
PAM_EXTERN
int pam_sm_open_session(pam_handle_t *pamh, int flags UNUSED,
int argc, const char **argv)
{
struct passwd *pw;
const char *username;
int ret, old_uid, uid, old_gid, gid, loop, force = 0;
for (loop = 0; loop < argc; loop++) {
if (strcmp(argv[loop], "force") == 0)
force = 1;
else if (strcmp(argv[loop], "debug") == 0)
xdebug = 1;
else if (strcmp(argv[loop], "revoke") == 0)
do_revoke = 1;
}
/* don't do anything if already created a keyring (will be called
* multiple times if mentioned more than once in a pam script)
*/
session_counter++;
debug(pamh, "OPEN %d", session_counter);
if (my_session_keyring > 0)
return PAM_SUCCESS;
/* look up the target UID */
ret = pam_get_user(pamh, &username, "key user");
if (ret != PAM_SUCCESS)
return ret;
pw = pam_modutil_getpwnam(pamh, username);
if (!pw) {
error(pamh, "Unable to look up user \"%s\"\n", username);
return PAM_USER_UNKNOWN;
}
uid = pw->pw_uid;
old_uid = getuid();
gid = pw->pw_gid;
old_gid = getgid();
debug(pamh, "UID:%d [%d] GID:%d [%d]", uid, old_uid, gid, old_gid);
/* switch to the real UID and GID so that the keyring ends up owned by
* the right user */
if (uid != old_uid && setreuid(uid, -1) < 0)
return error(pamh, "Unable to change UID to %d temporarily\n", uid);
if (gid != old_gid && setregid(gid, -1) < 0) {
error(pamh, "Unable to change GID to %d temporarily\n", gid);
setreuid(old_uid, -1);
return PAM_SESSION_ERR;
}
ret = init_keyrings(pamh, force);
/* return to the orignal UID and GID (probably root) */
if (uid != old_uid && setreuid(old_uid, -1) < 0)
ret = error(pamh, "Unable to change UID back to %d\n", old_uid);
if (gid != old_gid && setregid(old_gid, -1) < 0)
ret = error(pamh, "Unable to change GID back to %d\n", old_gid);
return ret;
}
/*
* close a PAM session by revoking the session keyring if requested
*/
PAM_EXTERN
int pam_sm_close_session(pam_handle_t *pamh, int flags UNUSED,
int argc UNUSED, const char **argv UNUSED)
{
debug(pamh, "CLOSE %d,%d,%d",
session_counter, my_session_keyring, do_revoke);
session_counter--;
if (session_counter == 0 && my_session_keyring > 0 && do_revoke)
kill_keyrings(pamh);
return PAM_SUCCESS;
}
#ifdef PAM_STATIC
/* static module data */
struct pam_module _pam_keyinit_modstruct = {
"pam_keyinit",
NULL,
NULL,
NULL,
pam_sm_open_session,
pam_sm_close_session,
NULL
};
#endif
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