Hello,
So I think my last attempt was misguided; attached is a simpler
reproducer that exhibits the problem following these steps:
1. create a socket, bind it, and mark it as O_NONBLOCK;
2. select on that socket to wait for an incoming connection;
3. clear its O_NONBLOCK flag;
4. call accept, which returns a connected socket;
5. notice that O_NONBLOCK is set on that new socket (it shouldn’t).
I believe the problem is that the connection is made why the original
socket is marked O_NONBLOCK, and pflocal’s ‘S_socket_connect’ inherits
that O_NONBLOCK flag in the socket it gets via ‘sock_clone’. The test
program later clears O_NONBLOCK but it has no effect since in pflocal
the connected socket has already been created with O_NONBLOCK and queued.
The patch below fixes that (and thus fixes the Shepherd socket
activation, as yelninei initially reported).
Thoughts?
Ludo’.
PS: I wanted to test my modified pflocal by setting it on an arbitrary
node and remapping but that kind of trick doesn’t work:
--8<---------------cut here---------------start------------->8---
ludo@childhurd ~$ settrans -ca pflocal-server /hurd/pflocal
ludo@childhurd ~$ ./remap /servers/socket/1 $PWD/pflocal-server -- ./simple
bind: Cannot assign requested address
settrans: fsys_goaway: (ipc/mig) server died
--8<---------------cut here---------------end--------------->8---
As Samuel found out, this is because /hurd/ifsock uses
/servers/socket/1 and there must be a “confused deputy” problem where
ifsock talks to the wrong pflocal.
#define _GNU_SOURCE 1
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <string.h>
#include <fcntl.h>
#include <error.h>
static void
terminate (const char *message)
{
perror (message);
exit (EXIT_FAILURE);
}
static void
child (const struct sockaddr *addr, socklen_t len)
{
int sock = socket (PF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0);
if (sock < 0) terminate ("socket");
int err = connect (sock, addr, len);
if (err) terminate ("connect");
static const char buf[] = "hello, world!\n";
ssize_t written = write (sock, buf, sizeof buf);
if (written < 0) terminate ("write");
exit (EXIT_SUCCESS);
}
int
main ()
{
int err;
int sock = socket (PF_UNIX, SOCK_STREAM | SOCK_NONBLOCK, 0);
if (sock < 0) terminate ("socket");
struct sockaddr_un addr;
addr.sun_family = AF_LOCAL;
strcpy (addr.sun_path, "/tmp/sock");
unlink ("/tmp/sock");
err = bind (sock, &addr, sizeof addr);
if (err) terminate ("bind");
err = listen (sock, 1);
if (err) terminate ("listen");
if (fork () == 0)
child ((struct sockaddr *) &addr, sizeof addr);
fd_set read_fds;
FD_ZERO (&read_fds);
FD_SET (sock, &read_fds);
struct timeval timeout = { .tv_sec = 100, .tv_usec = 0 };
err = select (FD_SETSIZE, &read_fds, NULL, NULL, &timeout);
if (err < 0) terminate ("select");
int flags = fcntl (sock, F_GETFL);
err = fcntl (sock, F_SETFL, flags & ~O_NONBLOCK);
if (err) terminate ("F_SETFL");
if ((fcntl (sock, F_GETFL) & O_NONBLOCK) != 0)
printf ("sock %d O_NONBLOCK!\n", sock);
struct sockaddr_storage peer;
socklen_t len;
int connection = accept (sock, (struct sockaddr *) &peer, &len);
if (connection < 0) terminate ("accept");
if ((fcntl (connection, F_GETFL) & O_NONBLOCK) != 0)
printf ("connection %d O_NONBLOCK!\n", connection);
char buf[1024];
err = read (connection, buf, sizeof buf);
if (err < 0) terminate ("read");
printf ("read '%s'\n", buf);
}
>From 5d55fd67221696187c697bbdc5067f617059e8fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <[email protected]>
Date: Thu, 8 May 2025 23:11:36 +0200
Subject: [PATCH] pflocal: Do not inherit PFLOCAL_SOCK_NONBLOCK across
connect/accept.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Previously, ‘accept’ would return an O_NONBLOCK socket if the listening
socket was O_NONBLOCK at the time the connection was made. With this
change, ‘accept’ always returns a socket where O_NONBLOCK is cleared.
---
pflocal/sock.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/pflocal/sock.c b/pflocal/sock.c
index 90c618ec..6bc061d6 100644
--- a/pflocal/sock.c
+++ b/pflocal/sock.c
@@ -1,6 +1,6 @@
/* Sock functions
- Copyright (C) 1995,96,2000,01,02, 2005 Free Software Foundation, Inc.
+ Copyright (C) 1995,96,2000,01,02, 2005, 2025 Free Software Foundation, Inc.
Written by Miles Bader <[email protected]>
This program is free software; you can redistribute it and/or
@@ -167,8 +167,11 @@ sock_clone (struct sock *template, struct sock **sock)
if (err)
return err;
- /* Copy some properties from TEMPLATE. */
- (*sock)->flags = template->flags & ~PFLOCAL_SOCK_CONNECTED;
+ /* Copy some properties from TEMPLATE. Clear O_NONBLOCK because the socket
+ returned by 'accept' must not inherit O_NONBLOCK from the parent
+ socket. */
+ (*sock)->flags =
+ template->flags & ~(PFLOCAL_SOCK_CONNECTED | PFLOCAL_SOCK_NONBLOCK);
return 0;
}
base-commit: 50f494ee743a0892380eebfbf428f398bc3b40f5
--
2.49.0
