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 (x2).

On 29/10/2018 16:32, Adhemerval Zanella wrote:
> 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;
>>  	    }
>>  	}
>>