busybox/loginutils/login.c

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/* vi: set sw=4 ts=4: */
/*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
*/
#include "busybox.h"
#include <utmp.h>
#include <sys/resource.h>
#include <syslog.h>
#ifdef CONFIG_SELINUX
#include <selinux/selinux.h> /* for is_selinux_enabled() */
#include <selinux/get_context_list.h> /* for get_default_context() */
#include <selinux/flask.h> /* for security class definitions */
#include <errno.h>
#endif
enum {
TIMEOUT = 60,
EMPTY_USERNAME_COUNT = 10,
USERNAME_SIZE = 32,
TTYNAME_SIZE = 32,
};
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static char full_tty[TTYNAME_SIZE];
static char* short_tty = full_tty;
#if ENABLE_FEATURE_UTMP
/* vv Taken from tinylogin utmp.c vv */
/*
* read_or_build_utent - see if utmp file is correct for this process
*
* System V is very picky about the contents of the utmp file
* and requires that a slot for the current process exist.
* The utmp file is scanned for an entry with the same process
* ID. If no entry exists the process exits with a message.
*
* The "picky" flag is for network and other logins that may
* use special flags. It allows the pid checks to be overridden.
* This means that getty should never invoke login with any
* command line flags.
*/
static struct utmp utent;
static void read_or_build_utent(int picky)
{
struct utmp *ut;
pid_t pid = getpid();
setutent();
/* First, try to find a valid utmp entry for this process. */
while ((ut = getutent()))
if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
(ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
break;
/* If there is one, just use it, otherwise create a new one. */
if (ut) {
utent = *ut;
} else {
if (picky)
bb_error_msg_and_die("no utmp entry found");
memset(&utent, 0, sizeof(utent));
utent.ut_type = LOGIN_PROCESS;
utent.ut_pid = pid;
strncpy(utent.ut_line, short_tty, sizeof(utent.ut_line));
/* This one is only 4 chars wide. Try to fit something
* remotely meaningful by skipping "tty"... */
strncpy(utent.ut_id, short_tty + 3, sizeof(utent.ut_id));
strncpy(utent.ut_user, "LOGIN", sizeof(utent.ut_user));
utent.ut_time = time(NULL);
}
if (!picky) /* root login */
memset(utent.ut_host, 0, sizeof(utent.ut_host));
}
/*
* write_utent - put a USER_PROCESS entry in the utmp file
*
* write_utent changes the type of the current utmp entry to
* USER_PROCESS. the wtmp file will be updated as well.
*/
static void write_utent(const char *username)
{
utent.ut_type = USER_PROCESS;
strncpy(utent.ut_user, username, sizeof(utent.ut_user));
utent.ut_time = time(NULL);
/* other fields already filled in by read_or_build_utent above */
setutent();
pututline(&utent);
endutent();
#if ENABLE_FEATURE_WTMP
if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
close(creat(bb_path_wtmp_file, 0664));
}
updwtmp(bb_path_wtmp_file, &utent);
#endif
}
#else /* !ENABLE_FEATURE_UTMP */
static inline void read_or_build_utent(int ATTRIBUTE_UNUSED picky) {}
static inline void write_utent(const char ATTRIBUTE_UNUSED *username) {}
#endif /* !ENABLE_FEATURE_UTMP */
static void die_if_nologin_and_non_root(int amroot)
{
FILE *fp;
int c;
if (access(bb_path_nologin_file, F_OK))
return;
fp = fopen(bb_path_nologin_file, "r");
if (fp) {
while ((c = getc(fp)) != EOF)
putchar((c=='\n') ? '\r' : c);
fflush(stdout);
fclose(fp);
} else
puts("\r\nSystem closed for routine maintenance\r");
if (!amroot)
exit(1);
puts("\r\n[Disconnect bypassed -- root login allowed.]\r");
}
#if ENABLE_FEATURE_SECURETTY
static int check_securetty(void)
{
FILE *fp;
int i;
char buf[BUFSIZ];
fp = fopen(bb_path_securetty_file, "r");
if (!fp) {
/* A missing securetty file is not an error. */
return 1;
}
while (fgets(buf, sizeof(buf)-1, fp)) {
for (i = strlen(buf)-1; i>=0; --i) {
if (!isspace(buf[i]))
break;
}
buf[++i] = '\0';
if ((buf[0]=='\0') || (buf[0]=='#'))
continue;
if (strcmp(buf, short_tty) == 0) {
fclose(fp);
return 1;
}
}
fclose(fp);
return 0;
}
#else
static inline int check_securetty(void) { return 1; }
#endif
static void get_username_or_die(char *buf, int size_buf)
{
int c, cntdown;
cntdown = EMPTY_USERNAME_COUNT;
prompt:
/* skip whitespace */
print_login_prompt();
do {
c = getchar();
if (c == EOF) exit(1);
if (c == '\n') {
if (!--cntdown) exit(1);
goto prompt;
}
} while (isspace(c));
*buf++ = c;
if (!fgets(buf, size_buf-2, stdin))
exit(1);
if (!strchr(buf, '\n'))
exit(1);
while (isgraph(*buf)) buf++;
*buf = '\0';
}
static void motd(void)
{
FILE *fp;
int c;
fp = fopen(bb_path_motd_file, "r");
if (fp) {
while ((c = getc(fp)) != EOF)
putchar(c);
fclose(fp);
}
}
static void nonblock(int fd)
{
fcntl(fd, F_SETFL, O_NONBLOCK | fcntl(fd, F_GETFL));
}
static void alarm_handler(int sig ATTRIBUTE_UNUSED)
{
/* This is the escape hatch! Poor serial line users and the like
* arrive here when their connection is broken.
* We don't want to block here */
nonblock(1);
nonblock(2);
bb_info_msg("\r\nLogin timed out after %d seconds\r", TIMEOUT);
exit(EXIT_SUCCESS);
}
int login_main(int argc, char **argv);
int login_main(int argc, char **argv)
{
enum {
LOGIN_OPT_f = (1<<0),
LOGIN_OPT_h = (1<<1),
LOGIN_OPT_p = (1<<2),
};
char fromhost[512];
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char username[USERNAME_SIZE];
const char *tmp;
int amroot;
unsigned opt;
int count = 0;
struct passwd *pw;
char *opt_host = NULL;
char *opt_user = NULL;
USE_SELINUX(security_context_t user_sid = NULL;)
username[0] = '\0';
amroot = (getuid() == 0);
signal(SIGALRM, alarm_handler);
alarm(TIMEOUT);
opt = getopt32(argc, argv, "f:h:p", &opt_user, &opt_host);
if (opt & LOGIN_OPT_f) {
if (!amroot)
bb_error_msg_and_die("-f is for root only");
safe_strncpy(username, opt_user, sizeof(username));
}
if (optind < argc) /* user from command line (getty) */
safe_strncpy(username, argv[optind], sizeof(username));
/* Let's find out and memorize our tty */
if (!isatty(0) || !isatty(1) || !isatty(2))
return EXIT_FAILURE; /* Must be a terminal */
safe_strncpy(full_tty, "UNKNOWN", sizeof(full_tty));
tmp = ttyname(0);
if (tmp) {
safe_strncpy(full_tty, tmp, sizeof(full_tty));
if (strncmp(full_tty, "/dev/", 5) == 0)
short_tty = full_tty + 5;
}
read_or_build_utent(!amroot);
if (opt_host) {
USE_FEATURE_UTMP(
safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
)
snprintf(fromhost, sizeof(fromhost)-1, " on '%.100s' from "
"'%.200s'", short_tty, opt_host);
}
else
snprintf(fromhost, sizeof(fromhost)-1, " on '%.100s'", short_tty);
bb_setpgrp;
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openlog(applet_name, LOG_PID | LOG_CONS | LOG_NOWAIT, LOG_AUTH);
while (1) {
if (!username[0])
get_username_or_die(username, sizeof(username));
pw = getpwnam(username);
if (!pw) {
safe_strncpy(username, "UNKNOWN", sizeof(username));
goto auth_failed;
}
if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
goto auth_failed;
if (opt & LOGIN_OPT_f)
break; /* -f USER: success without asking passwd */
if (pw->pw_uid == 0 && !check_securetty())
goto auth_failed;
/* Don't check the password if password entry is empty (!) */
if (!pw->pw_passwd[0])
break;
/* authorization takes place here */
if (correct_password(pw))
break;
auth_failed:
opt &= ~LOGIN_OPT_f;
bb_do_delay(FAIL_DELAY);
puts("Login incorrect");
if (++count == 3) {
syslog(LOG_WARNING, "invalid password for '%s'%s",
username, fromhost);
return EXIT_FAILURE;
}
username[0] = '\0';
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}
alarm(0);
die_if_nologin_and_non_root(pw->pw_uid == 0);
write_utent(username);
#ifdef CONFIG_SELINUX
if (is_selinux_enabled()) {
security_context_t old_tty_sid, new_tty_sid;
if (get_default_context(username, NULL, &user_sid)) {
bb_error_msg_and_die("cannot get SID for %s",
username);
}
if (getfilecon(full_tty, &old_tty_sid) < 0) {
bb_perror_msg_and_die("getfilecon(%s) failed",
full_tty);
}
if (security_compute_relabel(user_sid, old_tty_sid,
SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
bb_perror_msg_and_die("security_change_sid(%s) failed",
full_tty);
}
if (setfilecon(full_tty, new_tty_sid) != 0) {
bb_perror_msg_and_die("chsid(%s, %s) failed",
full_tty, new_tty_sid);
}
}
#endif
/* Try these, but don't complain if they fail.
* _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
fchown(0, pw->pw_uid, pw->pw_gid);
fchmod(0, 0600);
/* TODO: be nommu-friendly, use spawn? */
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if (ENABLE_LOGIN_SCRIPTS) {
char *script = getenv("LOGIN_PRE_SUID_SCRIPT");
if (script) {
char *t_argv[2] = { script, NULL };
switch (fork()) {
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case -1: break;
case 0: /* child */
xchdir("/");
setenv("LOGIN_TTY", full_tty, 1);
setenv("LOGIN_USER", pw->pw_name, 1);
setenv("LOGIN_UID", utoa(pw->pw_uid), 1);
setenv("LOGIN_GID", utoa(pw->pw_gid), 1);
setenv("LOGIN_SHELL", pw->pw_shell, 1);
BB_EXECVP(script, t_argv);
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exit(1);
default: /* parent */
wait(NULL);
}
}
}
change_identity(pw);
tmp = pw->pw_shell;
if (!tmp || !*tmp)
tmp = DEFAULT_SHELL;
setup_environment(tmp, 1, !(opt & LOGIN_OPT_p), pw);
motd();
if (pw->pw_uid == 0)
syslog(LOG_INFO, "root login%s", fromhost);
#ifdef CONFIG_SELINUX
/* well, a simple setexeccon() here would do the job as well,
* but let's play the game for now */
set_current_security_context(user_sid);
#endif
// util-linux login also does:
// /* start new session */
// setsid();
// /* TIOCSCTTY: steal tty from other process group */
// if (ioctl(0, TIOCSCTTY, 1)) error_msg...
/* set signals to defaults */
signal(SIGALRM, SIG_DFL);
/* Is this correct? This way user can ctrl-c out of /etc/profile,
* potentially creating security breach (tested with bash 3.0).
* But without this, bash 3.0 will not enable ctrl-c either.
* Maybe bash is buggy?
* Need to find out what standards say about /bin/login -
* should it leave SIGINT etc enabled or disabled? */
signal(SIGINT, SIG_DFL);
run_shell(tmp, 1, 0, 0); /* exec the shell finally */
return EXIT_FAILURE;
}