Daniel Verite wrote:
> 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 is obsolete, it's now INT_MAX instead of INT_MAX/2.
I would keep this comment but use UINT_MAX/2 instead.
> 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.
Yeah, you're right. We also need to cast "needed" to Size in the while
test; and the repalloc_huge() call no longer needs a cast.
I propose the attached.
Not sure if we also need to cast the assignment to str->maxlen in the
last line.
--
Álvaro Herrera https://www.2ndQuadrant.com/
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commit 1327c2eea9c7ca074d88bb167bd4c35338d2de0b[m
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
AuthorDate: Tue Jan 10 02:46:42 2017 -0300
CommitDate: Tue Jan 10 02:46:42 2017 -0300
Fix overflow check in StringInfo
A thinko I introduced in fa2fa9955280. Also, amend a similarly broken
comment.
Report and patch by Daniel Vérité.
Discussion:
https://postgr.es/m/1706e85e-60d2-494e-8a64-9af1e1b21...@manitou-mail.org
diff --git a/src/backend/lib/stringinfo.c b/src/backend/lib/stringinfo.c
index bdc204e..11d751a 100644
--- a/src/backend/lib/stringinfo.c
+++ b/src/backend/lib/stringinfo.c
@@ -313,19 +313,19 @@ enlargeStringInfo(StringInfo str, int needed)
* for efficiency, double the buffer size each time it overflows.
* Actually, we might need to more than double it if 'needed' is big...
*/
- newlen = 2 * str->maxlen;
- while (needed > newlen)
+ newlen = 2 * (Size) str->maxlen;
+ while ((Size) needed > newlen)
newlen = 2 * newlen;
/*
* Clamp to the limit in case we went past it. Note we are assuming
here
- * that limit <= INT_MAX/2, else the above loop could overflow. We will
+ * that limit <= UINT_MAX/2, else the above loop could overflow. We
will
* still have newlen >= needed.
*/
if (newlen > limit)
newlen = limit;
- str->data = (char *) repalloc_huge(str->data, (Size) newlen);
+ str->data = (char *) repalloc_huge(str->data, newlen);
str->maxlen = newlen;
}
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