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

[Adhemerval Zanella Netto]

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>