/*-
* Copyright (c) 2007 Robert N. M. Watson
* All rights reserved.
*
* 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
*/
/*
* Sockets serialize I/O in each direction in order to avoid interlacing of
* I/O by multiple processes or threcvs recving or sending the socket. This
* is done using some form of kernel lock (varies by kernel version), called
* "sblock" in FreeBSD. However, to avoid unkillable processes waiting on
* I/O that may be entirely controlled by a remote network endpoint, that
* lock acquisition must be interruptible.
*
* To test this, set up a local domain stream socket pair and a set of three
* processes. Two processes block in recv(), the first on sbwait (wait for
* I/O), and the second on the sblock waiting for the first to finish. A
* third process is responsible for signalling the second process, then
* writing to the socket. Depending on the error returned in the second
* process, we can tell whether the sblock wait was interrupted, or if
* instead the process only woke up when the write was performed.
*/
#include <sys/socket.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
static int interrupted;
static void
signal_handler(int signum __unused)
{
interrupted++;
}
/*
* Process that will perform a blocking recv on a UNIX domain socket. This
* should return one byte of data.
*/
static void
blocking_recver(int fd)
{
ssize_t len;
char ch;
len = recv(fd, &ch, sizeof(ch), 0);
if (len < 0)
err(-1, "FAIL: blocking_recver: recv");
if (len == 0)
errx(-1, "FAIL: blocking_recver: recv: eof");
if (len != 1)
errx(-1, "FAIL: blocking_recver: recv: %zd bytes", len);
if (interrupted)
errx(-1, "FAIL: blocking_recver: interrupted wrong pid");
}
/*
* Process that will perform a locking recv on a UNIX domain socket.
*
* This is where we figure out if the test worked or not. If it has failed,
* then recv() will return EOF, as the close() arrives before the signal,
* meaning that the wait for the sblock was not interrupted; if it has
* succeeded, we get EINTR as the signal interrupts the lock request.
*/
static void
locking_recver(int fd)
{
ssize_t len;
char ch;
if (sleep(1) != 0)
err(-1, "FAIL: locking_recver: sleep");
len = recv(fd, &ch, sizeof(ch), 0);
if (len < 0 && errno != EINTR)
err(-1, "FAIL: locking_recver: recv");
if (len < 0 && errno == EINTR) {
fprintf(stderr, "PASS\n");
exit(0);
}
if (len == 0)
errx(-1, "FAIL: locking_recver: recv: eof");
if (!interrupted)
errx(-1, "FAIL: locking_recver: not interrupted");
}
static void
signaller(pid_t locking_recver_pid, int fd)
{
ssize_t len;
char ch;
if (sleep(2) != 0) {
warn("signaller sleep(2)");
return;
}
if (kill(locking_recver_pid, SIGHUP) < 0) {
warn("signaller kill(%d)", locking_recver_pid);
return;
}
if (sleep(1) != 0) {
warn("signaller sleep(1)");
return;
}
len = send(fd, &ch, sizeof(ch), 0);
if (len < 0) {
warn("signaller send");
return;
}
if (len != sizeof(ch)) {
warnx("signaller send ret %zd", len);
return;
}
if (close(fd) < 0) {
warn("signaller close");
return;
}
if (sleep(1) != 0) {
warn("signaller sleep(1)");
return;
}
}
int
main(void)
{
int error, fds[2], recver_fd, sender_fd;
pid_t blocking_recver_pid;
pid_t locking_recver_pid;
struct sigaction sa;
if (sigaction(SIGHUP, NULL, &sa) < 0)
err(-1, "FAIL: sigaction(SIGHUP, NULL, &sa)");
sa.sa_handler = signal_handler;
if (sa.sa_flags & SA_RESTART)
printf("SIGHUP restartable by default (cleared)\n");
sa.sa_flags &= ~SA_RESTART;
if (sigaction(SIGHUP, &sa, NULL) < 0)
err(-1, "FAIL: sigaction(SIGHUP, &sa, NULL)");
#if 0
if (signal(SIGHUP, signal_handler) == SIG_ERR)
err(-1, "FAIL: signal(SIGHUP)");
#endif
if (socketpair(PF_LOCAL, SOCK_STREAM, 0, fds) < 0)
err(-1, "FAIL: socketpair(PF_LOCAL, SOGK_STREAM, 0)");
sender_fd = fds[0];
recver_fd = fds[1];
blocking_recver_pid = fork();
if (blocking_recver_pid < 0)
err(-1, "FAIL: fork");
if (blocking_recver_pid == 0) {
close(sender_fd);
blocking_recver(recver_fd);
exit(0);
}
locking_recver_pid = fork();
if (locking_recver_pid < 0) {
error = errno;
kill(blocking_recver_pid, SIGKILL);
errno = error;
err(-1, "FAIL: fork");
}
if (locking_recver_pid == 0) {
close(sender_fd);
locking_recver(recver_fd);
exit(0);
}
signaller(locking_recver_pid, sender_fd);
kill(blocking_recver_pid, SIGKILL);
kill(locking_recver_pid, SIGKILL);
exit(0);
}
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