Skip site navigation (1) Skip section navigation (2)

Re: [HACKERS] Open 6.4 items

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tom Ivar Helbekkmo <tih(at)nhh(dot)no>
Cc: hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Open 6.4 items
Date: 1998-10-09 15:01:29
Message-ID: 22954.907945289@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Ivar Helbekkmo <tih(at)nhh(dot)no> writes:
> Now I'm explicitly asking for at least one byte more than I need, and
> I'm pretty damn sure that I never touch that extra byte, but something
> seems to, since the problem goes away.  It's arrogant of me, I know,
> but barring a complete misunderstanding on my part of how variable
> size records work (or a stupid bug that I've been staring at for hours
> without seeing, of course), I'd say that something outside my code is
> at fault.  Any ideas as to how to try to find out?

Well, I hate to ruin your day, but coming pre-armed with the knowledge
that the code is writing one byte too many, it's pretty obvious that the
first loop in inet_net_pton_ipv4 does indeed do that.  Specifically at
			else if (size-- > 0)
				*++dst = 0, dirty = 0;
where, when size (the number of remaining destination bytes) is reduced
to 0, the code nonetheless advances dst and clears the next byte.
The loop logic is fundamentally faulty: you can't check for emsgsize
overflow until you get a digit that is supposed to go into another byte.
I'd try something like

	tmp = 0;
	ndigits = 0;           // ndigits is # of hex digits seen for cur byte
	while (ch = next hex digit)
	{
		n = numeric equivalent of ch;
		assert(n >= 0 && n <= 15);
		tmp = (tmp << 4) | n;
		if (++ndigits == 2)
		{
			if (size-- <= 0)
				goto emsgsize;
			*dst++ = (u_char) tmp;
			tmp = 0, ndigits = 0;
		}
	}
	if (ndigits)
		goto enoent;	// odd number of hex digits is bogus


BTW, shouldn't this routine clear out all "size" bytes of the
destination, even if the given data doesn't fill it all?  A memset
at the top might be worthwhile.

			regards, tom lane

Responses

pgsql-hackers by date

Next:From: Bruce MomjianDate: 1998-10-09 16:39:17
Subject: Re: [HACKERS] version functions (was NT port of PGSQL - success)
Previous:From: Jan WieckDate: 1998-10-09 14:07:21
Subject: Re: [HACKERS] PL patches (one more)

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group