Date: Sun, 23 Jun 2002 12:04:52 -0500 From: "Matthew D. Fuller" <fullermd@over-yonder.net> To: Paul Herman <pherman@frenchfries.net> Cc: "Geoffrey C. Speicher" <geoff@sea-incorporated.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: bug in pw, -STABLE [patch] Message-ID: <20020623170452.GG81018@over-yonder.net> In-Reply-To: <20020623094323.F38369-100000@mammoth.eat.frenchfries.net> References: <20020623160439.GE81018@over-yonder.net> <20020623094323.F38369-100000@mammoth.eat.frenchfries.net>
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On Sun, Jun 23, 2002 at 09:59:10AM -0700 I heard the voice of
Paul Herman, and lo! it spake thus:
>
> I can't imagine it would be too extensive of a rewrite. The temp
> file code could be kept, and in fileupd.c:fileupdate() instead of
> rename("/etc/master.passwd.new", "/etc/master.passwd"), it just
> copies the contents of the .new file into the original file (that
> has the O_EXLOCK.)
Yes, but that would open up the problem that cause the rename(2) to be
used in the first place; i.e., rename() is atomic; read(2)/write(2)'ing a
bunch of data isn't, so a system crash at the wrong time would leave you
with a partial master.passwd. It wouldn't be the end of the world, of
course, since you'd still have the [s]pwd.db, so you could login, and
you'd have the master.passwd.new, so you could recover, but you'd have to
notice it and catch it before pw(8) or friends ran again. rename(2)'s
guarantee is what saves you there. From the manpage:
int
rename(const char *from, const char *to);
[...]
Rename() guarantees that if to already exists, an instance of to will
always exist, even if the system should crash in the middle of the opera-
tion.
--
Matthew Fuller (MF4839) | fullermd@over-yonder.net
Systems/Network Administrator | http://www.over-yonder.net/~fullermd/
"The only reason I'm burning my candle at both ends, is because I
haven't figured out how to light the middle yet"
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