1 /*-
2 * Copyright (c) 2007 Robert N. M. Watson
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 /*
28 * Sockets serialize I/O in each direction in order to avoid interlacing of
29 * I/O by multiple processes or threcvs recving or sending the socket. This
30 * is done using some form of kernel lock (varies by kernel version), called
31 * "sblock" in FreeBSD. However, to avoid unkillable processes waiting on
32 * I/O that may be entirely controlled by a remote network endpoint, that
33 * lock acquisition must be interruptible.
34 *
35 * To test this, set up a local domain stream socket pair and a set of three
36 * processes. Two processes block in recv(), the first on sbwait (wait for
37 * I/O), and the second on the sblock waiting for the first to finish. A
38 * third process is responsible for signalling the second process, then
39 * writing to the socket. Depending on the error returned in the second
40 * process, we can tell whether the sblock wait was interrupted, or if
41 * instead the process only woke up when the write was performed.
42 */
43
44 #include <sys/socket.h>
45
46 #include <err.h>
47 #include <errno.h>
48 #include <signal.h>
49 #include <stdio.h>
50 #include <stdlib.h>
51 #include <unistd.h>
52
53 static int interrupted;
54 static void
signal_handler(int signum __unused)55 signal_handler(int signum __unused)
56 {
57
58 interrupted++;
59 }
60
61 /*
62 * Process that will perform a blocking recv on a UNIX domain socket. This
63 * should return one byte of data.
64 */
65 static void
blocking_recver(int fd)66 blocking_recver(int fd)
67 {
68 ssize_t len;
69 char ch;
70
71 len = recv(fd, &ch, sizeof(ch), 0);
72 if (len < 0)
73 err(-1, "FAIL: blocking_recver: recv");
74 if (len == 0)
75 errx(-1, "FAIL: blocking_recver: recv: eof");
76 if (len != 1)
77 errx(-1, "FAIL: blocking_recver: recv: %zd bytes", len);
78 if (interrupted)
79 errx(-1, "FAIL: blocking_recver: interrupted wrong pid");
80 }
81
82 /*
83 * Process that will perform a locking recv on a UNIX domain socket.
84 *
85 * This is where we figure out if the test worked or not. If it has failed,
86 * then recv() will return EOF, as the close() arrives before the signal,
87 * meaning that the wait for the sblock was not interrupted; if it has
88 * succeeded, we get EINTR as the signal interrupts the lock request.
89 */
90 static void
locking_recver(int fd)91 locking_recver(int fd)
92 {
93 ssize_t len;
94 char ch;
95
96 if (sleep(1) != 0)
97 err(-1, "FAIL: locking_recver: sleep");
98 len = recv(fd, &ch, sizeof(ch), 0);
99 if (len < 0 && errno != EINTR)
100 err(-1, "FAIL: locking_recver: recv");
101 if (len < 0 && errno == EINTR) {
102 fprintf(stderr, "PASS\n");
103 exit(0);
104 }
105 if (len == 0)
106 errx(-1, "FAIL: locking_recver: recv: eof");
107 if (!interrupted)
108 errx(-1, "FAIL: locking_recver: not interrupted");
109 }
110
111 static void
signaller(pid_t locking_recver_pid,int fd)112 signaller(pid_t locking_recver_pid, int fd)
113 {
114 ssize_t len;
115 char ch;
116
117 if (sleep(2) != 0) {
118 warn("signaller sleep(2)");
119 return;
120 }
121 if (kill(locking_recver_pid, SIGHUP) < 0) {
122 warn("signaller kill(%d)", locking_recver_pid);
123 return;
124 }
125 if (sleep(1) != 0) {
126 warn("signaller sleep(1)");
127 return;
128 }
129 len = send(fd, &ch, sizeof(ch), 0);
130 if (len < 0) {
131 warn("signaller send");
132 return;
133 }
134 if (len != sizeof(ch)) {
135 warnx("signaller send ret %zd", len);
136 return;
137 }
138 if (close(fd) < 0) {
139 warn("signaller close");
140 return;
141 }
142 if (sleep(1) != 0) {
143 warn("signaller sleep(1)");
144 return;
145 }
146 }
147
148 int
main(void)149 main(void)
150 {
151 int error, fds[2], recver_fd, sender_fd;
152 pid_t blocking_recver_pid;
153 pid_t locking_recver_pid;
154 struct sigaction sa;
155
156 if (sigaction(SIGHUP, NULL, &sa) < 0)
157 err(-1, "FAIL: sigaction(SIGHUP, NULL, &sa)");
158
159 sa.sa_handler = signal_handler;
160 if (sa.sa_flags & SA_RESTART)
161 printf("SIGHUP restartable by default (cleared)\n");
162 sa.sa_flags &= ~SA_RESTART;
163
164 if (sigaction(SIGHUP, &sa, NULL) < 0)
165 err(-1, "FAIL: sigaction(SIGHUP, &sa, NULL)");
166
167 #if 0
168 if (signal(SIGHUP, signal_handler) == SIG_ERR)
169 err(-1, "FAIL: signal(SIGHUP)");
170 #endif
171
172 if (socketpair(PF_LOCAL, SOCK_STREAM, 0, fds) < 0)
173 err(-1, "FAIL: socketpair(PF_LOCAL, SOGK_STREAM, 0)");
174
175 sender_fd = fds[0];
176 recver_fd = fds[1];
177
178 blocking_recver_pid = fork();
179 if (blocking_recver_pid < 0)
180 err(-1, "FAIL: fork");
181 if (blocking_recver_pid == 0) {
182 close(sender_fd);
183 blocking_recver(recver_fd);
184 exit(0);
185 }
186
187 locking_recver_pid = fork();
188 if (locking_recver_pid < 0) {
189 error = errno;
190 kill(blocking_recver_pid, SIGKILL);
191 errno = error;
192 err(-1, "FAIL: fork");
193 }
194 if (locking_recver_pid == 0) {
195 close(sender_fd);
196 locking_recver(recver_fd);
197 exit(0);
198 }
199
200 signaller(locking_recver_pid, sender_fd);
201
202 kill(blocking_recver_pid, SIGKILL);
203 kill(locking_recver_pid, SIGKILL);
204 exit(0);
205 }
206