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Re: pg_dump / copy bugs with "big lines" ?

From: "Daniel Verite" <daniel(at)manitou-mail(dot)org>
To: "Alvaro Herrera" <alvherre(at)2ndquadrant(dot)com>
Cc: "Tomas Vondra" <tomas(dot)vondra(at)2ndquadrant(dot)com>,"Craig Ringer" <craig(at)2ndquadrant(dot)com>,"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>,"Robert Haas" <robertmhaas(at)gmail(dot)com>,"Jim Nasby" <Jim(dot)Nasby(at)bluetreble(dot)com>,"Ronan Dunklau" <ronan(dot)dunklau(at)dalibo(dot)com>,"pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_dump / copy bugs with "big lines" ?
Date: 2016-12-05 09:57:24
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
	Alvaro Herrera wrote:

> I have now pushed this to 9.5, 9.6 and master.  It could be backpatched
> to 9.4 with ease (just a small change in heap_form_tuple); anything
> further back would require much more effort.
> I used a 32-bit limit using sizeof(int32).  I tested and all the
> mentioned cases seem to work sanely; if you can spare some more time to
> test what was committed, I'd appreciate it.

My tests are OK too but I see an issue with the code in
enlargeStringInfo(), regarding integer overflow.
The bit of comment that says:

  Note we are assuming here that limit <= INT_MAX/2, else the above
  loop could overflow.

is obsolete, it's now INT_MAX instead of INT_MAX/2.

There's a related problem here:
	newlen = 2 * str->maxlen;
	while (needed > newlen)
		newlen = 2 * newlen;
str->maxlen is an int going up to INT_MAX so [2 * str->maxlen] now
*will* overflow when [str->maxlen > INT_MAX/2].
Eventually it somehow works because of this:
	if (newlen > limit)
		newlen = limit;
but newlen is wonky (when resulting from int overflow)
before being brought back to limit.

PFA a minimal fix.

Best regards,
Daniel Vérité
PostgreSQL-powered mailer:
Twitter: @DanielVerite

Attachment: enlargestrinfo-fix.diff
Description: text/x-patch (861 bytes)

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