1/* Handle locking of password file.
2 Copyright (C) 1996-2016 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <http://www.gnu.org/licenses/>. */
19
20#include <fcntl.h>
21#include <libc-lock.h>
22#include <shadow.h>
23#include <signal.h>
24#include <string.h>
25#include <unistd.h>
26#include <sys/file.h>
27
28#include <kernel-features.h>
29
30
31/* Name of the lock file. */
32#define PWD_LOCKFILE "/etc/.pwd.lock"
33
34/* How long to wait for getting the lock before returning with an
35 error. */
36#define TIMEOUT 15 /* sec */
37
38
39/* File descriptor for lock file. */
40static int lock_fd = -1;
41
42/* Prevent problems in multithreaded program by using mutex. */
43__libc_lock_define_initialized (static, lock)
44
45
46/* Prototypes for local functions. */
47static void noop_handler (int __sig);
48
49
50/* We cannot simply return in error cases. We have to close the file
51 and perhaps restore the signal handler. */
52#define RETURN_CLOSE_FD(code) \
53 do { \
54 if ((code) < 0 && lock_fd >= 0) \
55 { \
56 __close (lock_fd); \
57 lock_fd = -1; \
58 } \
59 __libc_lock_unlock (lock); \
60 return (code); \
61 } while (0)
62
63#define RETURN_RESTORE_HANDLER(code) \
64 do { \
65 /* Restore old action handler for alarm. We don't need to know \
66 about the current one. */ \
67 __sigaction (SIGALRM, &saved_act, NULL); \
68 RETURN_CLOSE_FD (code); \
69 } while (0)
70
71#define RETURN_CLEAR_ALARM(code) \
72 do { \
73 /* Clear alarm. */ \
74 alarm (0); \
75 /* Restore old set of handled signals. We don't need to know \
76 about the current one.*/ \
77 __sigprocmask (SIG_SETMASK, &saved_set, NULL); \
78 RETURN_RESTORE_HANDLER (code); \
79 } while (0)
80
81
82int
83__lckpwdf (void)
84{
85 sigset_t saved_set; /* Saved set of caught signals. */
86 struct sigaction saved_act; /* Saved signal action. */
87 sigset_t new_set; /* New set of caught signals. */
88 struct sigaction new_act; /* New signal action. */
89 struct flock fl; /* Information struct for locking. */
90 int result;
91
92 if (lock_fd != -1)
93 /* Still locked by own process. */
94 return -1;
95
96 /* Prevent problems caused by multiple threads. */
97 __libc_lock_lock (lock);
98
99 int oflags = O_WRONLY | O_CREAT;
100#ifdef O_CLOEXEC
101 oflags |= O_CLOEXEC;
102#endif
103 lock_fd = __open (PWD_LOCKFILE, oflags, 0600);
104 if (lock_fd == -1)
105 /* Cannot create lock file. */
106 RETURN_CLOSE_FD (-1);
107
108#ifndef __ASSUME_O_CLOEXEC
109# ifdef O_CLOEXEC
110 if (__have_o_cloexec <= 0)
111# endif
112 {
113 /* Make sure file gets correctly closed when process finished. */
114 int flags = __fcntl (lock_fd, F_GETFD, 0);
115 if (flags == -1)
116 /* Cannot get file flags. */
117 RETURN_CLOSE_FD (-1);
118# ifdef O_CLOEXEC
119 if (__have_o_cloexec == 0)
120 __have_o_cloexec = (flags & FD_CLOEXEC) == 0 ? -1 : 1;
121 if (__have_o_cloexec < 0)
122# endif
123 {
124 flags |= FD_CLOEXEC; /* Close on exit. */
125 if (__fcntl (lock_fd, F_SETFD, flags) < 0)
126 /* Cannot set new flags. */
127 RETURN_CLOSE_FD (-1);
128 }
129 }
130#endif
131
132 /* Now we have to get exclusive write access. Since multiple
133 process could try this we won't stop when it first fails.
134 Instead we set a timeout for the system call. Once the timer
135 expires it is likely that there are some problems which cannot be
136 resolved by waiting.
137
138 It is important that we don't change the signal state. We must
139 restore the old signal behaviour. */
140 memset (&new_act, '\0', sizeof (struct sigaction));
141 new_act.sa_handler = noop_handler;
142 __sigfillset (&new_act.sa_mask);
143 new_act.sa_flags = 0ul;
144
145 /* Install new action handler for alarm and save old. */
146 if (__sigaction (SIGALRM, &new_act, &saved_act) < 0)
147 /* Cannot install signal handler. */
148 RETURN_CLOSE_FD (-1);
149
150 /* Now make sure the alarm signal is not blocked. */
151 __sigemptyset (&new_set);
152 __sigaddset (&new_set, SIGALRM);
153 if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
154 RETURN_RESTORE_HANDLER (-1);
155
156 /* Start timer. If we cannot get the lock in the specified time we
157 get a signal. */
158 alarm (TIMEOUT);
159
160 /* Try to get the lock. */
161 memset (&fl, '\0', sizeof (struct flock));
162 fl.l_type = F_WRLCK;
163 fl.l_whence = SEEK_SET;
164 result = __fcntl (lock_fd, F_SETLKW, &fl);
165
166 RETURN_CLEAR_ALARM (result);
167}
168weak_alias (__lckpwdf, lckpwdf)
169
170
171int
172__ulckpwdf (void)
173{
174 int result;
175
176 if (lock_fd == -1)
177 /* There is no lock set. */
178 result = -1;
179 else
180 {
181 /* Prevent problems caused by multiple threads. */
182 __libc_lock_lock (lock);
183
184 result = __close (lock_fd);
185
186 /* Mark descriptor as unused. */
187 lock_fd = -1;
188
189 /* Clear mutex. */
190 __libc_lock_unlock (lock);
191 }
192
193 return result;
194}
195weak_alias (__ulckpwdf, ulckpwdf)
196
197
198static void
199noop_handler (int sig)
200{
201 /* We simply return which makes the `fcntl' call return with an error. */
202}
203