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#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <security/pam_appl.h>
#include <security/pam_modules.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sched.h>
#include <dlfcn.h>
#define countof(_x) ((int)((sizeof((_x)) / sizeof((_x)[0]))))
struct module_args_t {
int (*callback)(pam_handle_t *, int, int, const char **);
pam_handle_t *handler;
int flags;
int argc;
const char **argv;
};
struct auth_module_t {
const char *name;
const char *path;
const char *symbol;
struct module_args_t args;
void *dl_handler;
pid_t pid;
bool active;
};
static
struct auth_module_t modules_g[] = {
{
.name = "unix",
.path = "/usr/lib/security/pam_unix.so",
.symbol = "pam_sm_authenticate",
},
};
static int multi_auth_init(pam_handle_t *pamh, int flags,
int argc, const char **argv)
{
for (int i = 0; i < countof(modules_g); ++i) {
struct auth_module_t *mod = &modules_g[i];
mod->dl_handler = dlopen(mod->path, RTLD_NOW);
if (mod->dl_handler == NULL) {
fprintf(stderr, "%s: %m\n", mod->path);
return PAM_SYSTEM_ERR;
}
mod->args.callback = dlsym(mod->dl_handler, mod->symbol);
mod->args.handler = pamh;
mod->args.flags = flags;
mod->args.argc = argc;
mod->args.argv = argv;
if (mod->args.callback == NULL) {
return PAM_SYSTEM_ERR;
}
}
return 0;
}
static void multi_auth_fini(void)
{
for (int i = 0; i < countof(modules_g); ++i) {
dlclose(modules_g[i].dl_handler);
}
}
static int module_auth_main(void *_args)
{
struct module_args_t *args = _args;
/* the child is supposed to close after returning from this function */
return args->callback(args->handler, args->flags, args->argc, args->argv);
}
static int perform_auth(void)
{
for (int i = 0; i < countof(modules_g); ++i) {
#define STACK_SIZE (1000 * 1000)
struct auth_module_t *mod = &modules_g[i];
void *stack = malloc(STACK_SIZE);
if (stack == NULL) {
return PAM_AUTH_ERR;
}
int clone_flags = CLONE_NEWUTS|SIGCHLD;
modules_g[i].pid = clone(module_auth_main, stack + STACK_SIZE, clone_flags, &mod->args);
modules_g[i].active = true;
if (modules_g[i].pid == -1) {
return PAM_SYSTEM_ERR;
}
#undef STACK_SIZE
}
siginfo_t infos;
int modules_terminated = 0;
int ret = PAM_AUTH_ERR;
do {
/* wait for a first child to exit or be killed */
waitid(P_ALL, 0, &infos, WEXITED);
++modules_terminated;
/* find the process matching the pid */
for (int i = 0; i < countof(modules_g); ++i) {
struct auth_module_t *mod = &modules_g[i];
if (mod->pid == infos.si_pid) {
mod->active = false;
break;
}
}
if (infos.si_status == PAM_SUCCESS || infos.si_status == PAM_AUTH_ERR) {
ret = infos.si_status;
break;
}
} while (modules_terminated < countof(modules_g));
for (int i = 0; i < countof(modules_g); ++i) {
struct auth_module_t *mod = &modules_g[i];
if (!mod->active)
continue;
kill(mod->pid, SIGKILL);
waitpid(mod->pid, NULL, 0);
}
return ret;
}
PAM_EXTERN
int pam_sm_setcred(pam_handle_t *pamh, int flags, int argc, const char **argv)
{
(void)pamh;
(void)flags;
(void)argc;
(void)argv;
return PAM_SUCCESS;
}
PAM_EXTERN
int pam_sm_authenticate(pam_handle_t *pamh, int flags,
int argc, const char **argv)
{
int ret = multi_auth_init(pamh, flags, argc, argv);
if (ret == 0) {
ret = perform_auth();
}
multi_auth_fini();
return ret;
}
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