daemon: recognise named Unix stdin sockets

clientserver.c

@@ -22,6 +22,9 @@
 #include "rsync.h"
 #include "itypes.h"
 #include "ifuncs.h"
+#ifdef HAVE_SYS_UN_H
+#include <sys/un.h>
+#endif
 
 extern int quiet;
 extern int dry_run;
@@ -1722,8 +1725,10 @@ static void become_daemon(void)
 	}
 }
 
-/* Inetd supplies a connected IP stream on stdin. Other launchers may use a
- * local socket for process I/O, which must not select inetd mode. */
+/* Inetd supplies a connected IP stream on stdin. Socket activation may also
+ * supply a connected Unix stream whose local endpoint has a name. Other
+ * launchers may use an unnamed local socket for process I/O, which must not
+ * select inetd mode. */
 static int is_inetd_socket(int fd)
 {
 	int type;
@@ -1736,11 +1741,38 @@ static int is_inetd_socket(int fd)
 	 || getpeername(fd, (struct sockaddr *)&peer, &peer_len) != 0)
 		return 0;
 
-	return peer.ss_family == AF_INET
+	if (peer.ss_family == AF_INET
 #ifdef INET6
-	    || peer.ss_family == AF_INET6
+	 || peer.ss_family == AF_INET6
 #endif
-	    ;
+	)
+		return 1;
+
+#ifdef HAVE_SYS_UN_H
+	if (peer.ss_family == AF_UNIX) {
+		struct sockaddr_storage local = {0};
+		struct sockaddr_un *local_un = (struct sockaddr_un *)&local;
+		socklen_t local_len = sizeof local;
+		size_t path_len, i;
+
+		if (getsockname(fd, (struct sockaddr *)&local, &local_len) != 0
+		 || local.ss_family != AF_UNIX)
+			return 0;
+
+		if (local_len <= (socklen_t)offsetof(struct sockaddr_un, sun_path))
+			return 0;
+		path_len = (size_t)local_len - offsetof(struct sockaddr_un, sun_path);
+		if (path_len > sizeof local_un->sun_path)
+			path_len = sizeof local_un->sun_path;
+		for (i = 0; i < path_len; i++) {
+			if (local_un->sun_path[i] != '\0')
+				return 1;
+		}
+		return 0;
+	}
+#endif
+
+	return 0;
 }
 
 int daemon_main(void)

testsuite/daemon-stdin-unix-listener_test.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""A named Unix listener on stdin selects inetd-style daemon mode."""
+
+import os
+import socket
+import subprocess
+import sys
+import tempfile
+
+from rsyncfns import (
+    SCRATCHDIR, claim_free_port, rmtree, rsync_argv, test_fail,
+    test_skipped, write_daemon_conf,
+)
+
+if not hasattr(socket, 'AF_UNIX'):
+    test_skipped('Unix-domain sockets are unavailable')
+if sys.platform == 'cygwin':
+    test_skipped('Cygwin cannot pass a named Unix listener as daemon stdin')
+
+base = SCRATCHDIR / 'daemon-stdin-unix-listener'
+rmtree(base)
+module = base / 'module'
+module.mkdir(parents=True)
+conf = write_daemon_conf([
+    ('module', {'path': str(module), 'read only': 'yes'}),
+])
+port = claim_free_port(12980)
+
+
+def check_listener(address, label):
+    listener = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    client = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    child = None
+    proc = None
+    try:
+        try:
+            listener.bind(address)
+            listener.listen(1)
+            client.connect(address)
+            child, _ = listener.accept()
+        except (OSError, ValueError) as e:
+            test_skipped(f'{label} Unix listener is unavailable: {e}')
+
+        proc = subprocess.Popen(
+            rsync_argv('--daemon', '--no-detach', f'--config={conf}',
+                       f'--port={port}'),
+            stdin=child.fileno(), stdout=child.fileno(),
+            stderr=subprocess.PIPE, close_fds=True,
+        )
+        child.close()
+        child = None
+
+        client.settimeout(2)
+        try:
+            greeting = client.recv(256)
+        except socket.timeout:
+            test_fail(f'{label}: daemon did not greet the accepted Unix connection')
+        if not greeting.startswith(b'@RSYNCD:'):
+            test_fail(f'{label}: unexpected daemon greeting: {greeting!r}')
+    finally:
+        if child is not None:
+            child.close()
+        client.close()
+        listener.close()
+        if proc is not None:
+            try:
+                proc.wait(timeout=2)
+            except subprocess.TimeoutExpired:
+                proc.terminate()
+                try:
+                    proc.wait(timeout=2)
+                except subprocess.TimeoutExpired:
+                    proc.kill()
+                    proc.wait(timeout=2)
+
+
+with tempfile.TemporaryDirectory(prefix='rsync-listener-') as tmpdir:
+    check_listener(f'{tmpdir}/rsyncd.sock', 'filesystem')
+
+if sys.platform.startswith('linux'):
+    # A leading NUL selects Linux's abstract Unix namespace.
+    check_listener(f'\0rsync-stdin-listener-{os.getpid()}', 'abstract')
+
+print('named Unix stdin listeners select inetd-style daemon mode')

testsuite/skiplist/cygwin.txt

@@ -29,6 +29,7 @@ daemon-module-chdir-symlink
 daemon-module-private-parent
 daemon-secrets-file-symlink
 daemon-stdin-local-socket             # Cygwin Python has no AF_UNIX socketpair
+daemon-stdin-unix-listener            # Cygwin cannot pass a named AF_UNIX listener as daemon stdin
 devices
 dir-sgid
 early-input-symlink