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glibc/shadow/lckpwdf.c
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/* Handle locking of password file. | |
Copyright (C) 1996-2016 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996. | |
The GNU C Library is free software; you can redistribute it and/or | |
modify it under the terms of the GNU Lesser General Public | |
License as published by the Free Software Foundation; either | |
version 2.1 of the License, or (at your option) any later version. | |
The GNU C Library is distributed in the hope that it will be useful, | |
but WITHOUT ANY WARRANTY; without even the implied warranty of | |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
Lesser General Public License for more details. | |
You should have received a copy of the GNU Lesser General Public | |
License along with the GNU C Library; if not, see | |
<http://www.gnu.org/licenses/>. */ | |
#include <fcntl.h> | |
#include <libc-lock.h> | |
#include <shadow.h> | |
#include <signal.h> | |
#include <string.h> | |
#include <unistd.h> | |
#include <sys/file.h> | |
#include <kernel-features.h> | |
/* Name of the lock file. */ | |
#define PWD_LOCKFILE "/etc/.pwd.lock" | |
/* How long to wait for getting the lock before returning with an | |
error. */ | |
#define TIMEOUT 15 /* sec */ | |
/* File descriptor for lock file. */ | |
static int lock_fd = -1; | |
/* Prevent problems in multithreaded program by using mutex. */ | |
__libc_lock_define_initialized (static, lock) | |
/* Prototypes for local functions. */ | |
static void noop_handler (int __sig); | |
/* We cannot simply return in error cases. We have to close the file | |
and perhaps restore the signal handler. */ | |
#define RETURN_CLOSE_FD(code) \ | |
do { \ | |
if ((code) < 0 && lock_fd >= 0) \ | |
{ \ | |
__close (lock_fd); \ | |
lock_fd = -1; \ | |
} \ | |
__libc_lock_unlock (lock); \ | |
return (code); \ | |
} while (0) | |
#define RETURN_RESTORE_HANDLER(code) \ | |
do { \ | |
/* Restore old action handler for alarm. We don't need to know \ | |
about the current one. */ \ | |
__sigaction (SIGALRM, &saved_act, NULL); \ | |
RETURN_CLOSE_FD (code); \ | |
} while (0) | |
#define RETURN_CLEAR_ALARM(code) \ | |
do { \ | |
/* Clear alarm. */ \ | |
alarm (0); \ | |
/* Restore old set of handled signals. We don't need to know \ | |
about the current one.*/ \ | |
__sigprocmask (SIG_SETMASK, &saved_set, NULL); \ | |
RETURN_RESTORE_HANDLER (code); \ | |
} while (0) | |
int | |
__lckpwdf (void) | |
{ | |
sigset_t saved_set; /* Saved set of caught signals. */ | |
struct sigaction saved_act; /* Saved signal action. */ | |
sigset_t new_set; /* New set of caught signals. */ | |
struct sigaction new_act; /* New signal action. */ | |
struct flock fl; /* Information struct for locking. */ | |
int result; | |
if (lock_fd != -1) | |
/* Still locked by own process. */ | |
return -1; | |
/* Prevent problems caused by multiple threads. */ | |
__libc_lock_lock (lock); | |
int oflags = O_WRONLY | O_CREAT; | |
#ifdef O_CLOEXEC | |
oflags |= O_CLOEXEC; | |
#endif | |
lock_fd = __open (PWD_LOCKFILE, oflags, 0600); | |
if (lock_fd == -1) | |
/* Cannot create lock file. */ | |
RETURN_CLOSE_FD (-1); | |
#ifndef __ASSUME_O_CLOEXEC | |
# ifdef O_CLOEXEC | |
if (__have_o_cloexec <= 0) | |
# endif | |
{ | |
/* Make sure file gets correctly closed when process finished. */ | |
int flags = __fcntl (lock_fd, F_GETFD, 0); | |
if (flags == -1) | |
/* Cannot get file flags. */ | |
RETURN_CLOSE_FD (-1); | |
# ifdef O_CLOEXEC | |
if (__have_o_cloexec == 0) | |
__have_o_cloexec = (flags & FD_CLOEXEC) == 0 ? -1 : 1; | |
if (__have_o_cloexec < 0) | |
# endif | |
{ | |
flags |= FD_CLOEXEC; /* Close on exit. */ | |
if (__fcntl (lock_fd, F_SETFD, flags) < 0) | |
/* Cannot set new flags. */ | |
RETURN_CLOSE_FD (-1); | |
} | |
} | |
#endif | |
/* Now we have to get exclusive write access. Since multiple | |
process could try this we won't stop when it first fails. | |
Instead we set a timeout for the system call. Once the timer | |
expires it is likely that there are some problems which cannot be | |
resolved by waiting. | |
It is important that we don't change the signal state. We must | |
restore the old signal behaviour. */ | |
memset (&new_act, '\0', sizeof (struct sigaction)); | |
new_act.sa_handler = noop_handler; | |
__sigfillset (&new_act.sa_mask); | |
new_act.sa_flags = 0ul; | |
/* Install new action handler for alarm and save old. */ | |
if (__sigaction (SIGALRM, &new_act, &saved_act) < 0) | |
/* Cannot install signal handler. */ | |
RETURN_CLOSE_FD (-1); | |
/* Now make sure the alarm signal is not blocked. */ | |
__sigemptyset (&new_set); | |
__sigaddset (&new_set, SIGALRM); | |
if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0) | |
RETURN_RESTORE_HANDLER (-1); | |
/* Start timer. If we cannot get the lock in the specified time we | |
get a signal. */ | |
alarm (TIMEOUT); | |
/* Try to get the lock. */ | |
memset (&fl, '\0', sizeof (struct flock)); | |
fl.l_type = F_WRLCK; | |
fl.l_whence = SEEK_SET; | |
result = __fcntl (lock_fd, F_SETLKW, &fl); | |
RETURN_CLEAR_ALARM (result); | |
} | |
weak_alias (__lckpwdf, lckpwdf) | |
int | |
__ulckpwdf (void) | |
{ | |
int result; | |
if (lock_fd == -1) | |
/* There is no lock set. */ | |
result = -1; | |
else | |
{ | |
/* Prevent problems caused by multiple threads. */ | |
__libc_lock_lock (lock); | |
result = __close (lock_fd); | |
/* Mark descriptor as unused. */ | |
lock_fd = -1; | |
/* Clear mutex. */ | |
__libc_lock_unlock (lock); | |
} | |
return result; | |
} | |
weak_alias (__ulckpwdf, ulckpwdf) | |
static void | |
noop_handler (int sig) | |
{ | |
/* We simply return which makes the `fcntl' call return with an error. */ | |
} |