1/* Handle locking of password file.
2 Copyright (C) 1996-2021 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 <https://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#include <sigsetops.h>
28
29#include <kernel-features.h>
30
31
32/* Name of the lock file. */
33#define PWD_LOCKFILE "/etc/.pwd.lock"
34
35/* How long to wait for getting the lock before returning with an
36 error. */
37#define TIMEOUT 15 /* sec */
38
39
40/* File descriptor for lock file. */
41static int lock_fd = -1;
42
43/* Prevent problems in multithreaded program by using mutex. */
44__libc_lock_define_initialized (static, lock)
45
46
47/* Prototypes for local functions. */
48static void noop_handler (int __sig);
49
50
51/* We cannot simply return in error cases. We have to close the file
52 and perhaps restore the signal handler. */
53#define RETURN_CLOSE_FD(code) \
54 do { \
55 if ((code) < 0 && lock_fd >= 0) \
56 { \
57 __close (lock_fd); \
58 lock_fd = -1; \
59 } \
60 __libc_lock_unlock (lock); \
61 return (code); \
62 } while (0)
63
64#define RETURN_RESTORE_HANDLER(code) \
65 do { \
66 /* Restore old action handler for alarm. We don't need to know \
67 about the current one. */ \
68 __sigaction (SIGALRM, &saved_act, NULL); \
69 RETURN_CLOSE_FD (code); \
70 } while (0)
71
72#define RETURN_CLEAR_ALARM(code) \
73 do { \
74 /* Clear alarm. */ \
75 alarm (0); \
76 /* Restore old set of handled signals. We don't need to know \
77 about the current one.*/ \
78 __sigprocmask (SIG_SETMASK, &saved_set, NULL); \
79 RETURN_RESTORE_HANDLER (code); \
80 } while (0)
81
82
83int
84__lckpwdf (void)
85{
86 sigset_t saved_set; /* Saved set of caught signals. */
87 struct sigaction saved_act; /* Saved signal action. */
88 sigset_t new_set; /* New set of caught signals. */
89 struct sigaction new_act; /* New signal action. */
90 struct flock fl; /* Information struct for locking. */
91 int result;
92
93 if (lock_fd != -1)
94 /* Still locked by own process. */
95 return -1;
96
97 /* Prevent problems caused by multiple threads. */
98 __libc_lock_lock (lock);
99
100 int oflags = O_WRONLY | O_CREAT | O_CLOEXEC;
101 lock_fd = __open (PWD_LOCKFILE, oflags, 0600);
102 if (lock_fd == -1)
103 /* Cannot create lock file. */
104 RETURN_CLOSE_FD (-1);
105
106 /* Now we have to get exclusive write access. Since multiple
107 process could try this we won't stop when it first fails.
108 Instead we set a timeout for the system call. Once the timer
109 expires it is likely that there are some problems which cannot be
110 resolved by waiting.
111
112 It is important that we don't change the signal state. We must
113 restore the old signal behaviour. */
114 memset (&new_act, '\0', sizeof (struct sigaction));
115 new_act.sa_handler = noop_handler;
116 __sigfillset (&new_act.sa_mask);
117 new_act.sa_flags = 0ul;
118
119 /* Install new action handler for alarm and save old. */
120 if (__sigaction (SIGALRM, &new_act, &saved_act) < 0)
121 /* Cannot install signal handler. */
122 RETURN_CLOSE_FD (-1);
123
124 /* Now make sure the alarm signal is not blocked. */
125 __sigemptyset (&new_set);
126 __sigaddset (&new_set, SIGALRM);
127 if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
128 RETURN_RESTORE_HANDLER (-1);
129
130 /* Start timer. If we cannot get the lock in the specified time we
131 get a signal. */
132 alarm (TIMEOUT);
133
134 /* Try to get the lock. */
135 memset (&fl, '\0', sizeof (struct flock));
136 fl.l_type = F_WRLCK;
137 fl.l_whence = SEEK_SET;
138 result = __fcntl (lock_fd, F_SETLKW, &fl);
139
140 RETURN_CLEAR_ALARM (result);
141}
142weak_alias (__lckpwdf, lckpwdf)
143
144
145int
146__ulckpwdf (void)
147{
148 int result;
149
150 if (lock_fd == -1)
151 /* There is no lock set. */
152 result = -1;
153 else
154 {
155 /* Prevent problems caused by multiple threads. */
156 __libc_lock_lock (lock);
157
158 result = __close (lock_fd);
159
160 /* Mark descriptor as unused. */
161 lock_fd = -1;
162
163 /* Clear mutex. */
164 __libc_lock_unlock (lock);
165 }
166
167 return result;
168}
169weak_alias (__ulckpwdf, ulckpwdf)
170
171
172static void
173noop_handler (int sig)
174{
175 /* We simply return which makes the `fcntl' call return with an error. */
176}
177