treewide: use _exit() over exit()

In the podman CI I noticed many seccomp denials in our logs even though
tests passed:
comm="pasta.avx2" exe="/usr/bin/pasta.avx2" sig=31 arch=c000003e
syscall=202 compat=0 ip=0x7fb3d31f69db code=0x80000000

Which is futex being called and blocked by the pasta profile. After a
few tries I managed to reproduce locally with this loop in ~20 min:
while :;
  do podman run -d --network bridge quay.io/libpod/testimage:20241011 \
	sleep 100 && \
  sleep 10 && \
  podman rm -fa -t0
done

And using a pasta version with prctl(PR_SET_DUMPABLE, 1); set I got the
following stack trace:
Stack trace of thread 1:
  #0  0x00007fc95e6de91b __lll_lock_wait_private (libc.so.6 + 0x9491b)
  #1  0x00007fc95e68d6de __run_exit_handlers (libc.so.6 + 0x436de)
  #2  0x00007fc95e68d70e exit (libc.so.6 + 0x4370e)
  #3  0x000055f31b78c50b n/a (n/a + 0x0)
  #4  0x00007fc95e68d70e exit (libc.so.6 + 0x4370e)
  #5  0x000055f31b78d5a2 n/a (n/a + 0x0)

Pasta got killed in exit(), it seems glibc is trying to use a lock when
running exit handlers even though no exit handlers are defined.

Given no exit handlers are needed we can call _exit() instead. This
skips exit handlers and does not flush stdio streams compared to exit()
which should be fine for the use here.

Based on the input from Stefano I did not change the test/doc programs
or qrap as they do not use seccomp filters.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

conf.c

@@ -769,7 +769,7 @@ static void conf_ip6_local(struct ip6_ctx *ip6)
  * usage() - Print usage, exit with given status code
  * @name:	Executable name
  * @f:		Stream to print usage info to
- * @status:	Status code for exit()
+ * @status:	Status code for _exit()
  */
 static void usage(const char *name, FILE *f, int status)
 {
@@ -925,7 +925,7 @@ static void usage(const char *name, FILE *f, int status)
 		"    SPEC is as described for TCP above\n"
 		"    default: none\n");
 
-	exit(status);
+	_exit(status);
 
 pasta_opts:
 
@@ -980,7 +980,7 @@ pasta_opts:
 		"  --ns-mac-addr ADDR	Set MAC address on tap interface\n"
 		"  --no-splice		Disable inbound socket splicing\n");
 
-	exit(status);
+	_exit(status);
 }
 
 /**
@@ -1482,7 +1482,7 @@ void conf(struct ctx *c, int argc, char **argv)
 			FPRINTF(stdout,
 				c->mode == MODE_PASTA ? "pasta " : "passt ");
 			FPRINTF(stdout, VERSION_BLOB);
-			exit(EXIT_SUCCESS);
+			_exit(EXIT_SUCCESS);
 		case 15:
 			ret = snprintf(c->ip4.ifname_out,
 				       sizeof(c->ip4.ifname_out), "%s", optarg);

log.h

@@ -32,13 +32,13 @@ void logmsg_perror(int pri, const char *format, ...)
 #define die(...)							\
 	do {								\
 		err(__VA_ARGS__);					\
-		exit(EXIT_FAILURE);					\
+		_exit(EXIT_FAILURE);					\
 	} while (0)
 
 #define die_perror(...)							\
 	do {								\
 		err_perror(__VA_ARGS__);				\
-		exit(EXIT_FAILURE);					\
+		_exit(EXIT_FAILURE);					\
 	} while (0)
 
 extern int log_trace;

passt.c

@@ -167,7 +167,7 @@ void exit_handler(int signal)
 {
 	(void)signal;
 
-	exit(EXIT_SUCCESS);
+	_exit(EXIT_SUCCESS);
 }
 
 /**
@@ -210,7 +210,7 @@ int main(int argc, char **argv)
 	sigaction(SIGQUIT, &sa, NULL);
 
 	if (argc < 1)
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 
 	strncpy(argv0, argv[0], PATH_MAX - 1);
 	name = basename(argv0);
@@ -226,7 +226,7 @@ int main(int argc, char **argv)
 	} else if (strstr(name, "passt")) {
 		c.mode = MODE_PASST;
 	} else {
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 	}
 
 	madvise(pkt_buf, TAP_BUF_BYTES, MADV_HUGEPAGE);
@@ -259,7 +259,7 @@ int main(int argc, char **argv)
 	flow_init();
 
 	if ((!c.no_udp && udp_init(&c)) || (!c.no_tcp && tcp_init(&c)))
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 
 	proto_update_l2_buf(c.guest_mac, c.our_tap_mac);
 

pasta.c

@@ -73,12 +73,12 @@ void pasta_child_handler(int signal)
 	    !waitid(P_PID, pasta_child_pid, &infop, WEXITED | WNOHANG)) {
 		if (infop.si_pid == pasta_child_pid) {
 			if (infop.si_code == CLD_EXITED)
-				exit(infop.si_status);
+				_exit(infop.si_status);
 
 			/* If killed by a signal, si_status is the number.
 			 * Follow common shell convention of returning it + 128.
 			 */
-			exit(infop.si_status + 128);
+			_exit(infop.si_status + 128);
 
 			/* Nothing to do, detached PID namespace going away */
 		}
@@ -499,7 +499,7 @@ void pasta_netns_quit_inotify_handler(struct ctx *c, int inotify_fd)
 		return;
 
 	info("Namespace %s is gone, exiting", c->netns_base);
-	exit(EXIT_SUCCESS);
+	_exit(EXIT_SUCCESS);
 }
 
 /**
@@ -525,7 +525,7 @@ void pasta_netns_quit_timer_handler(struct ctx *c, union epoll_ref ref)
 			return;
 
 		info("Namespace %s is gone, exiting", c->netns_base);
-		exit(EXIT_SUCCESS);
+		_exit(EXIT_SUCCESS);
 	}
 
 	close(fd);

tap.c

@@ -1002,7 +1002,7 @@ void tap_sock_reset(struct ctx *c)
 	info("Client connection closed%s", c->one_off ? ", exiting" : "");
 
 	if (c->one_off)
-		exit(EXIT_SUCCESS);
+		_exit(EXIT_SUCCESS);
 
 	/* Close the connected socket, wait for a new connection */
 	epoll_del(c, c->fd_tap);

util.c

@@ -405,7 +405,7 @@ void pidfile_write(int fd, pid_t pid)
 
 	if (write(fd, pid_buf, n) < 0) {
 		perror("PID file write");
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 	}
 
 	close(fd);
@@ -441,12 +441,12 @@ int __daemon(int pidfile_fd, int devnull_fd)
 
 	if (pid == -1) {
 		perror("fork");
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 	}
 
 	if (pid) {
 		pidfile_write(pidfile_fd, pid);
-		exit(EXIT_SUCCESS);
+		_exit(EXIT_SUCCESS);
 	}
 
 	if (setsid()				< 0 ||
@@ -454,7 +454,7 @@ int __daemon(int pidfile_fd, int devnull_fd)
 	    dup2(devnull_fd, STDOUT_FILENO)	< 0 ||
 	    dup2(devnull_fd, STDERR_FILENO)	< 0 ||
 	    close(devnull_fd))
-		exit(EXIT_FAILURE);
+		_exit(EXIT_FAILURE);
 
 	return 0;
 }

vhost_user.c

@@ -60,7 +60,7 @@ void vu_print_capabilities(void)
 	info("{");
 	info("  \"type\": \"net\"");
 	info("}");
-	exit(EXIT_SUCCESS);
+	_exit(EXIT_SUCCESS);
 }
 
 /**