1 /*
2 * Copyright (c) 2001 Markus Friedl. All rights reserved.
3 * Copyright (c) 2021 Darren Tucker (dtucker at dtucker net).
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 ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26 #include "includes.h"
27 #ifndef HAVE_PSELECT
28
29 #include <sys/types.h>
30 #include <sys/time.h>
31 #ifdef HAVE_SYS_SELECT_H
32 # include <sys/select.h>
33 #endif
34
35 #include <errno.h>
36 #include <fcntl.h>
37 #include <signal.h>
38 #include <stdlib.h>
39 #include <string.h>
40 #include <unistd.h>
41
42 #include "log.h"
43 #include "misc.h" /* for set_nonblock */
44
45 #ifndef HAVE_SIGHANDLER_T
46 typedef void (*sighandler_t)(int);
47 #endif
48
49 static sighandler_t saved_sighandler[_NSIG];
50
51 /*
52 * Set up the descriptors. Because they are close-on-exec, in the case
53 * where sshd's re-exec fails notify_pipe will still point to a descriptor
54 * that was closed by the exec attempt but if that descriptor has been
55 * reopened then we'll attempt to use that. Ensure that notify_pipe is
56 * outside of the range used by sshd re-exec but within NFDBITS (so we don't
57 * need to expand the fd_sets).
58 */
59 #define REEXEC_MIN_FREE_FD (STDERR_FILENO + 4)
60 static int
pselect_notify_setup_fd(int * fd)61 pselect_notify_setup_fd(int *fd)
62 {
63 int r;
64
65 if ((r = fcntl(*fd, F_DUPFD, REEXEC_MIN_FREE_FD)) < 0 ||
66 fcntl(r, F_SETFD, FD_CLOEXEC) < 0 || r >= FD_SETSIZE)
67 return -1;
68 (void)close(*fd);
69 return (*fd = r);
70 }
71
72 /*
73 * we write to this pipe if a SIGCHLD is caught in order to avoid
74 * the race between select() and child_terminated
75 */
76 static pid_t notify_pid;
77 static int notify_pipe[2];
78 static void
pselect_notify_setup(void)79 pselect_notify_setup(void)
80 {
81 static int initialized;
82
83 if (initialized && notify_pid == getpid())
84 return;
85 if (notify_pid == 0)
86 debug3_f("initializing");
87 else {
88 debug3_f("pid changed, reinitializing");
89 if (notify_pipe[0] != -1)
90 close(notify_pipe[0]);
91 if (notify_pipe[1] != -1)
92 close(notify_pipe[1]);
93 }
94 if (pipe(notify_pipe) == -1) {
95 error("pipe(notify_pipe) failed %s", strerror(errno));
96 } else if (pselect_notify_setup_fd(¬ify_pipe[0]) == -1 ||
97 pselect_notify_setup_fd(¬ify_pipe[1]) == -1) {
98 error("fcntl(notify_pipe, ...) failed %s", strerror(errno));
99 close(notify_pipe[0]);
100 close(notify_pipe[1]);
101 } else {
102 set_nonblock(notify_pipe[0]);
103 set_nonblock(notify_pipe[1]);
104 notify_pid = getpid();
105 debug3_f("pid %d saved %d pipe0 %d pipe1 %d", getpid(),
106 notify_pid, notify_pipe[0], notify_pipe[1]);
107 initialized = 1;
108 return;
109 }
110 notify_pipe[0] = -1; /* read end */
111 notify_pipe[1] = -1; /* write end */
112 }
113 static void
pselect_notify_parent(void)114 pselect_notify_parent(void)
115 {
116 if (notify_pipe[1] != -1)
117 (void)write(notify_pipe[1], "", 1);
118 }
119 static void
pselect_notify_prepare(fd_set * readset)120 pselect_notify_prepare(fd_set *readset)
121 {
122 if (notify_pipe[0] != -1)
123 FD_SET(notify_pipe[0], readset);
124 }
125 static void
pselect_notify_done(fd_set * readset)126 pselect_notify_done(fd_set *readset)
127 {
128 char c;
129
130 if (notify_pipe[0] != -1 && FD_ISSET(notify_pipe[0], readset)) {
131 while (read(notify_pipe[0], &c, 1) != -1)
132 debug2_f("reading");
133 FD_CLR(notify_pipe[0], readset);
134 }
135 }
136
137 /*ARGSUSED*/
138 static void
pselect_sig_handler(int sig)139 pselect_sig_handler(int sig)
140 {
141 int save_errno = errno;
142
143 pselect_notify_parent();
144 if (saved_sighandler[sig] != NULL)
145 (*saved_sighandler[sig])(sig); /* call original handler */
146 errno = save_errno;
147 }
148
149 /*
150 * A minimal implementation of pselect(2), built on top of select(2).
151 */
152
153 int
pselect(int nfds,fd_set * readfds,fd_set * writefds,fd_set * exceptfds,const struct timespec * timeout,const sigset_t * mask)154 pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
155 const struct timespec *timeout, const sigset_t *mask)
156 {
157 int ret, sig, saved_errno, unmasked = 0;
158 sigset_t osig;
159 struct sigaction sa, osa;
160 struct timeval tv, *tvp = NULL;
161
162 if (timeout != NULL) {
163 tv.tv_sec = timeout->tv_sec;
164 tv.tv_usec = timeout->tv_nsec / 1000;
165 tvp = &tv;
166 }
167 if (mask == NULL) /* no signal mask, just call select */
168 return select(nfds, readfds, writefds, exceptfds, tvp);
169
170 /* For each signal we're unmasking, install our handler if needed. */
171 for (sig = 0; sig < _NSIG; sig++) {
172 if (sig == SIGKILL || sig == SIGSTOP || sigismember(mask, sig))
173 continue;
174 if (sigaction(sig, NULL, &sa) == 0 &&
175 sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL) {
176 unmasked = 1;
177 if (sa.sa_handler == pselect_sig_handler)
178 continue;
179 sa.sa_handler = pselect_sig_handler;
180 if (sigaction(sig, &sa, &osa) == 0) {
181 debug3_f("installing signal handler for %s, "
182 "previous %p", strsignal(sig),
183 osa.sa_handler);
184 saved_sighandler[sig] = osa.sa_handler;
185 }
186 }
187 }
188 if (unmasked) {
189 pselect_notify_setup();
190 pselect_notify_prepare(readfds);
191 nfds = MAX(nfds, notify_pipe[0] + 1);
192 }
193
194 /* Unmask signals, call select then restore signal mask. */
195 sigprocmask(SIG_SETMASK, mask, &osig);
196 ret = select(nfds, readfds, writefds, exceptfds, tvp);
197 saved_errno = errno;
198 sigprocmask(SIG_SETMASK, &osig, NULL);
199
200 if (unmasked)
201 pselect_notify_done(readfds);
202 errno = saved_errno;
203 return ret;
204 }
205 #endif
206