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

  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
  

On 17/04/23 10:39, Sergey Bugaev via Libc-alpha wrote:
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>

Add some description of what the test is accomplishing here.
Some small nits below, the patch LGTM.

> ---
> 
> 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";

Just remove the 'const' comment here.

> +  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>
  

Hello,

On Tue, Apr 18, 2023 at 3:13 PM Adhemerval Zanella Netto wrote:
> On 17/04/23 10:39, Sergey Bugaev via Libc-alpha wrote:
> > Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
>
> Add some description of what the test is accomplishing here.

Do you mean in the commit message? Done.

Also changed:
* in send_fd, memset the cmsg_storage to zero before filling it
* in send_fd, set msg_controllen to sizeof (cmsg_storage) (aka
  CMSG_SPACE (sizeof (fd))), not CMSG_LEN (sizeof (fd))
* dropped the /* const */

And here's the test passing on x86_64-linux:

socketpair(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, [3, 4]) = 0
sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=6}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[0]}], msg_controllen=24, msg_flags=0}, 0) = 6
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=100}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[5]}], msg_controllen=24, msg_flags=0}, 0) = 6
fcntl(5, F_GETFD)                       = 0
close(5)                                = 0
sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=6}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[0]}], msg_controllen=24, msg_flags=0}, 0) = 6
recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=100}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[5]}], msg_controllen=24, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 6
fcntl(5, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
close(5)                                = 0
close(3)                                = 0
close(4)                                = 0

Sergey

---- >8 ----

From 256a774a16e1bb3d721e2be82dc4bbab119bf6ea Mon Sep 17 00:00:00 2001
From: Sergey Bugaev <bugaevc@gmail.com>
Date: Mon, 17 Apr 2023 16:28:35 +0300
Subject: [RFC PATCH v3 4/4] socket: Add a test for MSG_CMSG_CLOEXEC

This checks that:
* We can send and receive fds over Unix domain sockets using SCM_RIGHTS;
* msg_controllen, cmsg_level, cmsg_type, cmsg_len are all filled in
  correctly on receive;
* Most importantly, the received fd has or has not the close-on-exec
  flag set depending on whether we pass MSG_CMSG_CLOEXEC to recvmsg ().

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 socket/Makefile           |   1 +
 socket/tst-cmsg_cloexec.c | 126 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 127 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..a18f4912
--- /dev/null
+++ b/socket/tst-cmsg_cloexec.c
@@ -0,0 +1,126 @@
+/* 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)
+{
+  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 = sizeof (cmsg_storage)
+    };
+
+  memset (&cmsg_storage, 0, sizeof (cmsg_storage));
+
+  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_SPACE (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>
  

On 18/04/23 12:37, Sergey Bugaev wrote:
> Hello,
> 
> On Tue, Apr 18, 2023 at 3:13 PM Adhemerval Zanella Netto wrote:
>> On 17/04/23 10:39, Sergey Bugaev via Libc-alpha wrote:
>>> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
>>
>> Add some description of what the test is accomplishing here.
> 
> Do you mean in the commit message? Done.
> 
> Also changed:
> * in send_fd, memset the cmsg_storage to zero before filling it
> * in send_fd, set msg_controllen to sizeof (cmsg_storage) (aka
>   CMSG_SPACE (sizeof (fd))), not CMSG_LEN (sizeof (fd))
> * dropped the /* const */
> 
> And here's the test passing on x86_64-linux:
> 
> socketpair(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, [3, 4]) = 0
> sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=6}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[0]}], msg_controllen=24, msg_flags=0}, 0) = 6
> recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=100}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[5]}], msg_controllen=24, msg_flags=0}, 0) = 6
> fcntl(5, F_GETFD)                       = 0
> close(5)                                = 0
> sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=6}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[0]}], msg_controllen=24, msg_flags=0}, 0) = 6
> recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="hello\0", iov_len=100}], msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, cmsg_data=[5]}], msg_controllen=24, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 6
> fcntl(5, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
> close(5)                                = 0
> close(3)                                = 0
> close(4)                                = 0
> 
> Sergey
> 
> ---- >8 ----
> 
> From 256a774a16e1bb3d721e2be82dc4bbab119bf6ea Mon Sep 17 00:00:00 2001
> From: Sergey Bugaev <bugaevc@gmail.com>
> Date: Mon, 17 Apr 2023 16:28:35 +0300
> Subject: [RFC PATCH v3 4/4] socket: Add a test for MSG_CMSG_CLOEXEC
> 
> This checks that:
> * We can send and receive fds over Unix domain sockets using SCM_RIGHTS;
> * msg_controllen, cmsg_level, cmsg_type, cmsg_len are all filled in
>   correctly on receive;
> * Most importantly, the received fd has or has not the close-on-exec
>   flag set depending on whether we pass MSG_CMSG_CLOEXEC to recvmsg ().
> 
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  socket/Makefile           |   1 +
>  socket/tst-cmsg_cloexec.c | 126 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 127 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..a18f4912
> --- /dev/null
> +++ b/socket/tst-cmsg_cloexec.c
> @@ -0,0 +1,126 @@
> +/* 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)
> +{
> +  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 = sizeof (cmsg_storage)
> +    };
> +
> +  memset (&cmsg_storage, 0, sizeof (cmsg_storage));
> +
> +  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_SPACE (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>