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is obsolete, it's now INT_MAX instead of INT_MAX/2.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: http://www.manitou-mail.org
Twitter: @DanielVerite
diff --git a/src/backend/lib/stringinfo.c b/src/backend/lib/stringinfo.c
index b618b37..b01afbe 100644
--- a/src/backend/lib/stringinfo.c
+++ b/src/backend/lib/stringinfo.c
@@ -313,14 +313,13 @@ 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;
+ newlen = 2 * (Size)str->maxlen; /* avoid integer overflow */
while (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
- * still have newlen >= needed.
+ * Clamp to the limit in case we went past it. We will still have
+ * newlen >= needed.
*/
if (newlen > limit)
newlen = limit;
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