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/*
* Copyright (c) 2001 Markus Friedl. All rights reserved.
* Copyright (c) 2021 Darren Tucker (dtucker at dtucker net).
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "includes.h"
#ifndef HAVE_PSELECT
#include <sys/types.h>
#include <sys/time.h>
#ifdef HAVE_SYS_SELECT_H
# include <sys/select.h>
#endif
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "log.h"
#include "misc.h" /* for set_nonblock */
#ifndef HAVE_SIGHANDLER_T
typedef void (*sighandler_t)(int);
#endif
static sighandler_t saved_sighandler[_NSIG];
/*
* Set up the descriptors. Because they are close-on-exec, in the case
* where sshd's re-exec fails notify_pipe will still point to a descriptor
* that was closed by the exec attempt but if that descriptor has been
* reopened then we'll attempt to use that. Ensure that notify_pipe is
* outside of the range used by sshd re-exec but within NFDBITS (so we don't
* need to expand the fd_sets).
*/
#define REEXEC_MIN_FREE_FD (STDERR_FILENO + 4)
static int
pselect_notify_setup_fd(int *fd)
{
int r;
if ((r = fcntl(*fd, F_DUPFD, REEXEC_MIN_FREE_FD)) < 0 ||
fcntl(r, F_SETFD, FD_CLOEXEC) < 0 || r >= FD_SETSIZE)
return -1;
(void)close(*fd);
return (*fd = r);
}
/*
* we write to this pipe if a SIGCHLD is caught in order to avoid
* the race between select() and child_terminated
*/
static pid_t notify_pid;
static int notify_pipe[2];
static void
pselect_notify_setup(void)
{
static int initialized;
if (initialized && notify_pid == getpid())
return;
if (notify_pid == 0)
debug3_f("initializing");
else {
debug3_f("pid changed, reinitializing");
if (notify_pipe[0] != -1)
close(notify_pipe[0]);
if (notify_pipe[1] != -1)
close(notify_pipe[1]);
}
if (pipe(notify_pipe) == -1) {
error("pipe(notify_pipe) failed %s", strerror(errno));
} else if (pselect_notify_setup_fd(¬ify_pipe[0]) == -1 ||
pselect_notify_setup_fd(¬ify_pipe[1]) == -1) {
error("fcntl(notify_pipe, ...) failed %s", strerror(errno));
close(notify_pipe[0]);
close(notify_pipe[1]);
} else {
set_nonblock(notify_pipe[0]);
set_nonblock(notify_pipe[1]);
notify_pid = getpid();
debug3_f("pid %d saved %d pipe0 %d pipe1 %d", getpid(),
notify_pid, notify_pipe[0], notify_pipe[1]);
initialized = 1;
return;
}
notify_pipe[0] = -1; /* read end */
notify_pipe[1] = -1; /* write end */
}
static void
pselect_notify_parent(void)
{
if (notify_pipe[1] != -1)
(void)write(notify_pipe[1], "", 1);
}
static void
pselect_notify_prepare(fd_set *readset)
{
if (notify_pipe[0] != -1)
FD_SET(notify_pipe[0], readset);
}
static void
pselect_notify_done(fd_set *readset)
{
char c;
if (notify_pipe[0] != -1 && FD_ISSET(notify_pipe[0], readset)) {
while (read(notify_pipe[0], &c, 1) != -1)
debug2_f("reading");
FD_CLR(notify_pipe[0], readset);
}
}
/*ARGSUSED*/
static void
pselect_sig_handler(int sig)
{
int save_errno = errno;
pselect_notify_parent();
if (saved_sighandler[sig] != NULL)
(*saved_sighandler[sig])(sig); /* call original handler */
errno = save_errno;
}
/*
* A minimal implementation of pselect(2), built on top of select(2).
*/
int
pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
const struct timespec *timeout, const sigset_t *mask)
{
int ret, sig, saved_errno, unmasked = 0;
sigset_t osig;
struct sigaction sa, osa;
struct timeval tv, *tvp = NULL;
if (timeout != NULL) {
tv.tv_sec = timeout->tv_sec;
tv.tv_usec = timeout->tv_nsec / 1000;
tvp = &tv;
}
if (mask == NULL) /* no signal mask, just call select */
return select(nfds, readfds, writefds, exceptfds, tvp);
/* For each signal we're unmasking, install our handler if needed. */
for (sig = 0; sig < _NSIG; sig++) {
if (sig == SIGKILL || sig == SIGSTOP || sigismember(mask, sig))
continue;
if (sigaction(sig, NULL, &sa) == 0 &&
sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL) {
unmasked = 1;
if (sa.sa_handler == pselect_sig_handler)
continue;
sa.sa_handler = pselect_sig_handler;
if (sigaction(sig, &sa, &osa) == 0) {
debug3_f("installing signal handler for %s, "
"previous %p", strsignal(sig),
osa.sa_handler);
saved_sighandler[sig] = osa.sa_handler;
}
}
}
if (unmasked) {
pselect_notify_setup();
pselect_notify_prepare(readfds);
nfds = MAX(nfds, notify_pipe[0] + 1);
}
/* Unmask signals, call select then restore signal mask. */
sigprocmask(SIG_SETMASK, mask, &osig);
ret = select(nfds, readfds, writefds, exceptfds, tvp);
saved_errno = errno;
sigprocmask(SIG_SETMASK, &osig, NULL);
if (unmasked)
pselect_notify_done(readfds);
errno = saved_errno;
return ret;
}
#endif
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