Date: Fri, 05 Nov 1999 16:08:04 -0200 From: Fabio Dias <duwde@elitenet.com.br> To: Philip Inglesant <philip@dircon.net> Cc: freebsd-stable@FreeBSD.ORG Subject: Re: Password file updating Message-ID: <38231D04.AD517B79@elitenet.com.br> References: <000501bf27bf$95b706a0$f12170c2@desktop97.dircon.co.uk>
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Philip Inglesant wrote:
> When the server end of this password update system gets a request, it
> flock()s master.password, makes a temporary copy of /etc/master.passwd,
> /etc/passwd, /etc/pwd.db, and /etc/spwd.db, and uses ordinary write() to the
> update passwd and master.passwd copies and dbopen() etc to update these
> temporary copies of pwd.db and spwd.db. I copied this source from the
> standard pwd_mkdb FreeeBSD source, with minor modifications.
I think you should update only a temporary copy of master.passwd, and
them
call pwd_mkdb(8), as does chpass(1), passwd(1), vipw(8) and all others.
> But once the update to the temporary files is done, of course my program has
> to update the real live files. It does this using rename().
>
> I am pretty sure that it is during the tiny period of time that the rename()
> is happening that the problem occurs.
quoting from pwd_mkdb(8) man page :
--
Because of the necessity for atomic update of the password files,
pwd_mkdb uses rename(2) to install them. This, however, requires
that
the file specified on the command line live on the same file system
as
the /etc directory.
There are the obvious races with multiple people running pwd_mkdb
on dif-
ferent password files at the same time. The front-ends to
pwd_mkdb,
chpass(1), passwd(1) and vipw(8), handle the locking necessary to
avoid
this problem.
--
rename(2) does a atomic update, your problem seems to rely on the
front-end
you're using, not on rename(2) itself. As I said before, update only a
temporary copy of master.passwd (as all password programs does) but take
care of the locking scheme utilized by those programs, and them call
pwd_mkdb(8).
Check out chpass/passwd/vipw sources.
Fabio Dias
duwde@elitenet.com.br
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