[RFC PATCH 4/4] socket: Add a test for MSG_CMSG_CLOEXEC

[Sergey Bugaev]

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---

This is an attempt to write a test, roughly based on
sysdeps/unix/sysv/linux/tst-scm_rights.c

Please tell me if this needs any changes. For instance, I opted to do
my own error checking for sendmsg/recvmsg/socketpair, but I could've
alternatively added xsendmsg/xrecvmsg/xsocketpair. This is also looser
on the coding style side, e.g. variables are defined mid-function
instead of upfront, since that's what I saw in tst-scm_rights.c; I can
get rid of that if that's not intended.

I placed this into the generic socket/ since it should also work on
Linux (though I only tested it on i686-gnu myself). Please tell me if
this would be better suited for sysdeps/mach/hurd/ instead.

 socket/Makefile           |   1 +
 socket/tst-cmsg_cloexec.c | 124 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 socket/tst-cmsg_cloexec.c

diff --git a/socket/Makefile b/socket/Makefile
index fffed7dd..94951ae3 100644
--- a/socket/Makefile
+++ b/socket/Makefile
@@ -35,6 +35,7 @@ tests := \
   tst-accept4 \
   tst-sockopt \
   tst-cmsghdr \
+  tst-cmsg_cloexec \
   # tests
 
 tests-internal := \
diff --git a/socket/tst-cmsg_cloexec.c b/socket/tst-cmsg_cloexec.c
new file mode 100644
index 00000000..237c3db2
--- /dev/null
+++ b/socket/tst-cmsg_cloexec.c
@@ -0,0 +1,124 @@
+/* Smoke test for MSG_CMSG_CLOEXEC.
+   Copyright (C) 2021-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <support/xunistd.h>
+#include <support/check.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <string.h>
+#include <fcntl.h>
+
+static void
+send_fd (int sockfd, int fd)
+{
+  /* const */ char data[] = "hello";
+  struct iovec iov = { .iov_base = data, .iov_len = sizeof (data) };
+
+  union
+  {
+    struct cmsghdr header;
+    char bytes[CMSG_SPACE (sizeof (fd))];
+  } cmsg_storage;
+
+  struct msghdr msg =
+    {
+      .msg_iov = &iov,
+      .msg_iovlen = 1,
+      .msg_control = cmsg_storage.bytes,
+      .msg_controllen = CMSG_LEN (sizeof (fd))
+    };
+
+  struct cmsghdr *cmsg = CMSG_FIRSTHDR (&msg);
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
+  memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
+
+  ssize_t nsent = sendmsg (sockfd, &msg, 0);
+  if (nsent < 0)
+    FAIL_EXIT1 ("sendmsg (%d): %m", sockfd);
+  TEST_COMPARE (nsent, sizeof (data));
+}
+
+static int
+recv_fd (int sockfd, int flags)
+{
+  char buffer[100];
+  struct iovec iov = { .iov_base = buffer, .iov_len = sizeof (buffer) };
+
+  union
+  {
+    struct cmsghdr header;
+    char bytes[100];
+  } cmsg_storage;
+
+  struct msghdr msg =
+    {
+      .msg_iov = &iov,
+      .msg_iovlen = 1,
+      .msg_control = cmsg_storage.bytes,
+      .msg_controllen = sizeof (cmsg_storage)
+    };
+
+  ssize_t nrecv = recvmsg (sockfd, &msg, flags);
+  if (nrecv < 0)
+    FAIL_EXIT1 ("recvmsg (%d): %m", sockfd);
+
+  TEST_COMPARE (msg.msg_controllen, CMSG_LEN (sizeof (int)));
+  struct cmsghdr *cmsg = CMSG_FIRSTHDR (&msg);
+  TEST_COMPARE (cmsg->cmsg_level, SOL_SOCKET);
+  TEST_COMPARE (cmsg->cmsg_type, SCM_RIGHTS);
+  TEST_COMPARE (cmsg->cmsg_len, CMSG_LEN (sizeof (int)));
+
+  int fd;
+  memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
+  return fd;
+}
+
+static int
+do_test (void)
+{
+  int sockfd[2];
+  int newfd;
+  int flags;
+  int rc = socketpair (AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, sockfd);
+  if (rc < 0)
+    FAIL_EXIT1 ("socketpair: %m");
+
+  send_fd (sockfd[1], STDIN_FILENO);
+  newfd = recv_fd (sockfd[0], 0);
+  TEST_VERIFY_EXIT (newfd > 0);
+  flags = fcntl (newfd, F_GETFD, 0);
+  TEST_VERIFY_EXIT (flags != -1);
+  TEST_VERIFY (!(flags & FD_CLOEXEC));
+  xclose (newfd);
+
+  send_fd (sockfd[1], STDIN_FILENO);
+  newfd = recv_fd (sockfd[0], MSG_CMSG_CLOEXEC);
+  TEST_VERIFY_EXIT (newfd > 0);
+  flags = fcntl (newfd, F_GETFD, 0);
+  TEST_VERIFY_EXIT (flags != -1);
+  TEST_VERIFY (flags & FD_CLOEXEC);
+  xclose (newfd);
+
+  xclose (sockfd[0]);
+  xclose (sockfd[1]);
+  return 0;
+}
+
+#include <support/test-driver.c>
-- 
2.39.2