Subject: Re: need for end*ent()?
To: John Nemeth <firstname.lastname@example.org>
From: Steven M. Bellovin <email@example.com>
Date: 09/14/2005 04:15:31
In message <200509140810.j8E8AEcN028511@vtn1.victoria.tc.ca>, John Nemeth write
>On Feb 3, 10:26pm, "Steven M. Bellovin" wrote:
>} In message <200509140707.j8E77lfP011272@vtn1.victoria.tc.ca>, John Nemeth wr
>} >On Dec 30, 7:52pm, Hubert Feyrer wrote:
>} >} On Tue, 13 Sep 2005, John Nemeth wrote:
>} >} > I am working on libwrap to remove a reference to getgrnam().
>} >} > Immediately after the use of getgrnam(), it calls endgrent() (there is
>} >} > also a call to endpwent()). I'm considering removing these in order to
>} >} > reduce possible side effects on applications using the library.
>} >} > However, I'm wondering if they should be left to ensure database
>} >} > updates are seen in long running daemons as per this paragraph in the
>} >} > manpage:
>} >} >
>} >} > It is dangerous for long-running programs to keep the file descript
>} >} > open as the database will become out of date if it is updated while
>} >} > program is running.
>} >} >
>} >} > Does anybody else have any thoughts on this issue?
>} >} The calls exist and are being used (properly) for the stated reason.
>} >} Why would you want to remove them?
>} > Because if the application happens to iterating a database by
>} >using getgrent() or getpwent() at the time it makes a call to libwrap I
>} >wouldn't want its pointer to be reset. I have no idea why an
>} >application would do this. However, I don't think it is up to me or
>} >necessarily up to any particular library to make this choice for it.
>} If that's the case, you're already in trouble, I think -- won't
>} getpwnam_r() reset the pointer? The man page doesn't say (and I
>} haven't looked at the code because I'm trying to assess expected
>} behavior), but it does say
>} Calling getpwent_r() from multiple threads will result in
>} each thread reading a disjoint portion of the password database.
> getpwent_r() isn't called by the library, just getgrnam() and
>getpwnam_r() (it will be getgrnam_r() when I'm done).
I know that getpwent_r() isn't called; that's the ambiguity in the man
page that I'm talking about: it doesn't say what happens to the pointer
if getpwnam_r() is called. I quoted the text about getpwent_r() to
show that one of the related functions would cause trouble. Sorry I
didn't make that clear.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb