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Fix possible internal overflow in numeric multiplication. 

mul_var() postpones propagating carries until it risks overflow in its
internal digit array.  However, the logic failed to account for the
possibility of overflow in the carry propagation step, allowing wrong
results to be generated in corner cases.  We must slightly reduce the
when-to-propagate-carries threshold to avoid that.

Discovered and fixed by Dean Rasheed, with small adjustments by me.

This has been wrong since commit d72f6c7503,
so back-patch to all supported branches.
This commit is contained in:
Tom Lane 2015-09-21 12:11:32 -04:00
parent 24aed2124a
commit a89781e347
3 changed files with 49 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/backend/utils/adt/numeric.c
View File

@ -4191,9 +4191,15 @@ mul_var(NumericVar *var1, NumericVar *var2, NumericVar *result,
* to avoid normalizing carries immediately.
*
* maxdig tracks the maximum possible value of any dig[] entry; when this
* threatens to exceed INT_MAX, we take the time to propagate carries. To
* avoid overflow in maxdig itself, it actually represents the max
* possible value divided by NBASE-1.
* threatens to exceed INT_MAX, we take the time to propagate carries.
* Furthermore, we need to ensure that overflow doesn't occur during the
* carry propagation passes either. The carry values could be as much as
* INT_MAX/NBASE, so really we must normalize when digits threaten to
* exceed INT_MAX - INT_MAX/NBASE.
*
* To avoid overflow in maxdig itself, it actually represents the max
* possible value divided by NBASE-1, ie, at the top of the loop it is
* known that no dig[] entry exceeds maxdig * (NBASE-1).
*/
dig = (int *) palloc0(res_ndigits * sizeof(int));
maxdig = 0;
@ -4208,7 +4214,7 @@ mul_var(NumericVar *var1, NumericVar *var2, NumericVar *result,
/* Time to normalize? */
maxdig += var1digit;
if (maxdig > INT_MAX / (NBASE - 1))
if (maxdig > (INT_MAX - INT_MAX / NBASE) / (NBASE - 1))
{
/* Yes, do it */
carry = 0;

27
src/test/regress/expected/numeric.out
View File

@ -1309,6 +1309,33 @@ SELECT * FROM num_input_test;
NaN
(7 rows)
--
-- Test some corner cases for multiplication
--
select 4790999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
?column?
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
47909999999999999999999999999999999999999999999999999999999999999999999999999999999999985209000000000000000000000000000000000000000000000000000000000000000000000000000000000001
(1 row)
select 4789999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
?column?
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
47899999999999999999999999999999999999999999999999999999999999999999999999999999999999985210000000000000000000000000000000000000000000000000000000000000000000000000000000000001
(1 row)
select 4770999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
?column?
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
47709999999999999999999999999999999999999999999999999999999999999999999999999999999999985229000000000000000000000000000000000000000000000000000000000000000000000000000000000001
(1 row)
select 4769999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
?column?
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
47699999999999999999999999999999999999999999999999999999999999999999999999999999999999985230000000000000000000000000000000000000000000000000000000000000000000000000000000000001
(1 row)
--
-- Test some corner cases for division
--

12
src/test/regress/sql/numeric.sql
View File

@ -811,6 +811,18 @@ INSERT INTO num_input_test(n1) VALUES (' N aN ');
SELECT * FROM num_input_test;
--
-- Test some corner cases for multiplication
--
select 4790999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
select 4789999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
select 4770999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
select 4769999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
--
-- Test some corner cases for division
--