Re: [PATCH 2/2] posix: Clear close-on-exec for posix_spawn adddup2 (BZ#23640)

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

Ping.

On 19/09/2018 19:46, adhemerval.zanella@linaro.org wrote:
> From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> 
> Austin Group issue #411 [1] proposes that posix_spawn file action
> posix_spawn_file_actions_adddup2 resets the close-on-exec when
> source and destination refer to same file descriptor.
> 
> It solves the issue on multi-thread applications which uses
> close-on-exec as default, and want to hand-chose specifically
> file descriptor to purposefully inherited into a child process.
> Current approach to achieve this scenario is to use two adddup2 file
> actions and a temporary file description which do not conflict with
> any other, coupled with a close file action to avoid leaking the
> temporary file descriptor.  This approach, besides being complex,
> may fail with EMFILE/ENFILE file descriptor exaustion.
> 
> This can be more easily accomplished with an in-place removal of
> FD_CLOEXEC.  Although the resulting adddup2 semantic is slight
> different than dup2 (equal file descriptors should be handled as
> no-op), the proposed possible solution are either more complex
> (fcntl action which a limited set of operations) or results in
> unrequired operations (dup3 which also returns EINVAL for same
> file descriptor).
> 
> Checked on aarch64-linux-gnu.
> 
> 	* posix/tst-spawn.c (do_prepare, handle_restart, do_test): Add
> 	posix_spawn_file_actions_adddup2 test to check O_CLOCEXEC reset.
> 	* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Add
> 	close-on-exec reset for adddup2 file action.
> 	* sysdeps/posix/spawni.c (__spawni_child): Likewise.
> 
> [1] http://austingroupbugs.net/view.php?id=411
> ---
>  ChangeLog                        |  6 ++++
>  posix/tst-spawn.c                | 47 +++++++++++++++++++++++++-------
>  sysdeps/posix/spawni.c           | 21 ++++++++++++--
>  sysdeps/unix/sysv/linux/spawni.c | 21 ++++++++++++--
>  4 files changed, 79 insertions(+), 16 deletions(-)
> 
> diff --git a/posix/tst-spawn.c b/posix/tst-spawn.c
> index 638ba1ba55..2354417020 100644
> --- a/posix/tst-spawn.c
> +++ b/posix/tst-spawn.c
> @@ -40,17 +40,19 @@ static int restart;
>  static char *name1;
>  static char *name2;
>  static char *name3;
> +static char *name5;
>  
>  /* Descriptors for the temporary files.  */
>  static int temp_fd1 = -1;
>  static int temp_fd2 = -1;
>  static int temp_fd3 = -1;
> +static int temp_fd5 = -1;
>  
>  /* The contents of our files.  */
>  static const char fd1string[] = "This file should get closed";
>  static const char fd2string[] = "This file should stay opened";
>  static const char fd3string[] = "This file will be opened";
> -
> +static const char fd5string[] = "This file should stay opened (O_CLOEXEC)";
>  
>  /* We have a preparation function.  */
>  static void
> @@ -63,24 +65,31 @@ do_prepare (int argc, char *argv[])
>    TEST_VERIFY_EXIT ((temp_fd1 = create_temp_file ("spawn", &name1)) != -1);
>    TEST_VERIFY_EXIT ((temp_fd2 = create_temp_file ("spawn", &name2)) != -1);
>    TEST_VERIFY_EXIT ((temp_fd3 = create_temp_file ("spawn", &name3)) != -1);
> +  TEST_VERIFY_EXIT ((temp_fd5 = create_temp_file ("spawn", &name5)) != -1);
> +
> +  int flags;
> +  TEST_VERIFY_EXIT ((flags = fcntl (temp_fd5, F_GETFD, &flags)) != -1);
> +  TEST_VERIFY_EXIT (fcntl (temp_fd5, F_SETFD, flags | FD_CLOEXEC) == 0);
>  }
>  #define PREPARE do_prepare
>  
>  static int
>  handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
> -		const char *fd4s, const char *name)
> +		const char *fd4s, const char *name, const char *fd5s)
>  {
>    char buf[100];
>    int fd1;
>    int fd2;
>    int fd3;
>    int fd4;
> +  int fd5;
>  
>    /* First get the descriptors.  */
>    fd1 = atol (fd1s);
>    fd2 = atol (fd2s);
>    fd3 = atol (fd3s);
>    fd4 = atol (fd4s);
> +  fd5 = atol (fd5s);
>  
>    /* Sanity check.  */
>    TEST_VERIFY_EXIT (fd1 != fd2);
> @@ -89,6 +98,7 @@ handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
>    TEST_VERIFY_EXIT (fd2 != fd3);
>    TEST_VERIFY_EXIT (fd2 != fd4);
>    TEST_VERIFY_EXIT (fd3 != fd4);
> +  TEST_VERIFY_EXIT (fd4 != fd5);
>  
>    /* First the easy part: read from the file descriptor which is
>       supposed to be open.  */
> @@ -116,6 +126,10 @@ handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
>    TEST_VERIFY_EXIT (read (fd1, buf, sizeof buf) == strlen (fd1string));
>    TEST_VERIFY_EXIT (memcmp (fd1string, buf, strlen (fd1string)) == 0);
>  
> +  TEST_VERIFY_EXIT (lseek (fd5, 0, SEEK_SET) == 0);
> +  TEST_VERIFY_EXIT (read (fd5, buf, sizeof buf) == strlen (fd5string));
> +  TEST_VERIFY_EXIT (memcmp (fd5string, buf, strlen (fd5string)) == 0);
> +
>    return 0;
>  }
>  
> @@ -131,6 +145,7 @@ do_test (int argc, char *argv[])
>    char fd2name[18];
>    char fd3name[18];
>    char fd4name[18];
> +  char fd5name[18];
>    char *name3_copy;
>    char *spargv[12];
>    int i;
> @@ -141,21 +156,24 @@ do_test (int argc, char *argv[])
>         + "--library-path"	optional
>         + the library path	optional
>         + the application name
> -     - five parameters left if called through re-execution
> +     - six parameters left if called through re-execution
>         + file descriptor number which is supposed to be closed
>         + the open file descriptor
>         + the newly opened file descriptor
> -       + thhe duped second descriptor
> +       + the duped second descriptor
>         + the name of the closed descriptor
> +       + the duped fourth dile descriptor which O_CLOEXEC should be
> +	 remove by adddup2.
>    */
> -  if (argc != (restart ? 6 : 2) && argc != (restart ? 6 : 5))
> +  if (argc != (restart ? 7 : 2) && argc != (restart ? 7 : 5))
>      FAIL_EXIT1 ("wrong number of arguments (%d)", argc);
>  
>    if (restart)
> -    return handle_restart (argv[1], argv[2], argv[3], argv[4], argv[5]);
> +    return handle_restart (argv[1], argv[2], argv[3], argv[4], argv[5],
> +			   argv[6]);
>  
> -  /* Prepare the test.  We are creating two files: one which file descriptor
> -     will be marked with FD_CLOEXEC, another which is not.  */
> +  /* Prepare the test.  We are creating four files: two which file descriptor
> +     will be marked with FD_CLOEXEC, another which is not  */
>  
>    /* Write something in the files.  */
>    TEST_VERIFY_EXIT (write (temp_fd1, fd1string, strlen (fd1string))
> @@ -164,6 +182,8 @@ do_test (int argc, char *argv[])
>  		    == strlen (fd2string));
>    TEST_VERIFY_EXIT (write (temp_fd3, fd3string, strlen (fd3string))
>  		    == strlen (fd3string));
> +  TEST_VERIFY_EXIT (write (temp_fd5, fd5string, strlen (fd5string))
> +		    == strlen (fd5string));
>  
>    /* Close the third file.  It'll be opened by `spawn'.  */
>    close (temp_fd3);
> @@ -183,17 +203,23 @@ do_test (int argc, char *argv[])
>    memset (name3_copy, 'X', strlen (name3_copy));
>  
>    /* We dup the second descriptor.  */
> -  fd4 = MAX (2, MAX (temp_fd1, MAX (temp_fd2, temp_fd3))) + 1;
> +  fd4 = MAX (2, MAX (temp_fd1, MAX (temp_fd2, MAX (temp_fd3, temp_fd5)))) + 1;
>    TEST_VERIFY_EXIT (posix_spawn_file_actions_adddup2 (&actions, temp_fd2,
>  						      fd4) == 0);
>  
> +  /* We clear the O_CLOEXEC on fourth descriptor, so it should be
> +     stay open on child.  */
> +  TEST_VERIFY_EXIT (posix_spawn_file_actions_adddup2 (&actions, temp_fd5,
> +						      temp_fd5) == 0);
> +
>    /* Now spawn the process.  */
>    snprintf (fd1name, sizeof fd1name, "%d", temp_fd1);
>    snprintf (fd2name, sizeof fd2name, "%d", temp_fd2);
>    snprintf (fd3name, sizeof fd3name, "%d", temp_fd3);
>    snprintf (fd4name, sizeof fd4name, "%d", fd4);
> +  snprintf (fd5name, sizeof fd5name, "%d", temp_fd5);
>  
> -  for (i = 0; i < (argc == (restart ? 6 : 5) ? 4 : 1); i++)
> +  for (i = 0; i < (argc == (restart ? 7 : 5) ? 4 : 1); i++)
>      spargv[i] = argv[i + 1];
>    spargv[i++] = (char *) "--direct";
>    spargv[i++] = (char *) "--restart";
> @@ -202,6 +228,7 @@ do_test (int argc, char *argv[])
>    spargv[i++] = fd3name;
>    spargv[i++] = fd4name;
>    spargv[i++] = name1;
> +  spargv[i++] = fd5name;
>    spargv[i] = NULL;
>  
>    TEST_VERIFY_EXIT (posix_spawn (&pid, argv[1], &actions, NULL, spargv,
> diff --git a/sysdeps/posix/spawni.c b/sysdeps/posix/spawni.c
> index b138ab4393..d322db5c19 100644
> --- a/sysdeps/posix/spawni.c
> +++ b/sysdeps/posix/spawni.c
> @@ -204,10 +204,25 @@ __spawni_child (void *arguments)
>  	      break;
>  
>  	    case spawn_do_dup2:
> -	      if (__dup2 (action->action.dup2_action.fd,
> -			  action->action.dup2_action.newfd)
> +	      /* Austin Group issue #411 requires adddup2 action with source
> +		 and destination being equal to remove close-on-exec flag.  */
> +	      if (action->action.dup2_action.fd
>  		  != action->action.dup2_action.newfd)
> -		goto fail;
> +		{
> +		  if (__dup2 (action->action.dup2_action.fd,
> +			     action->action.dup2_action.newfd)
> +		      != action->action.dup2_action.newfd)
> +		    goto fail;
> +		}
> +	      else
> +		{
> +		  int fd = action->action.dup2_action.newfd;
> +		  int flags = __fcntl (fd, F_GETFD, 0);
> +		  if (flags == -1)
> +		    goto fail;
> +		  if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
> +		    goto fail;
> +		}
>  	      break;
>  	    }
>  	}
> diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c
> index 85239cedbf..b2304ffe60 100644
> --- a/sysdeps/unix/sysv/linux/spawni.c
> +++ b/sysdeps/unix/sysv/linux/spawni.c
> @@ -253,10 +253,25 @@ __spawni_child (void *arguments)
>  	      break;
>  
>  	    case spawn_do_dup2:
> -	      if (__dup2 (action->action.dup2_action.fd,
> -			  action->action.dup2_action.newfd)
> +	      /* Austin Group issue #411 requires adddup2 action with source
> +		 and destination being equal to remove close-on-exec flag.  */
> +	      if (action->action.dup2_action.fd
>  		  != action->action.dup2_action.newfd)
> -		goto fail;
> +		{
> +		  if (__dup2 (action->action.dup2_action.fd,
> +			     action->action.dup2_action.newfd)
> +		      != action->action.dup2_action.newfd)
> +		    goto fail;
> +		}
> +	      else
> +		{
> +		  int fd = action->action.dup2_action.newfd;
> +		  int flags = __fcntl (fd, F_GETFD, 0);
> +		  if (flags == -1)
> +		    goto fail;
> +		  if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
> +		    goto fail;
> +		}
>  	      break;
>  	    }
>  	}
>