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. */ |
40 | static 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. */ |
47 | static 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 | |
82 | int |
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 | } |
168 | weak_alias (__lckpwdf, lckpwdf) |
169 | |
170 | |
171 | int |
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 | } |
195 | weak_alias (__ulckpwdf, ulckpwdf) |
196 | |
197 | |
198 | static void |
199 | noop_handler (int sig) |
200 | { |
201 | /* We simply return which makes the `fcntl' call return with an error. */ |
202 | } |
203 | |