From: Tom Lane Date: Mon, 21 Sep 2015 16:11:32 +0000 (-0400) Subject: Fix possible internal overflow in numeric multiplication. X-Git-Tag: REL9_6_BETA1~1335 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=246693e5ae8a36f015294aa8c73dbbf0d4e542a8;p=postgresql 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 d72f6c75038d8d37e64a29a04b911f728044d83b, so back-patch to all supported branches. --- diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c index 1bfa29e1b2..1667d8093f 100644 --- a/src/backend/utils/adt/numeric.c +++ b/src/backend/utils/adt/numeric.c @@ -5789,9 +5789,15 @@ 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; @@ -5806,7 +5812,7 @@ 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; diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.out index e6ee548e7c..c1886fd663 100644 --- a/src/test/regress/expected/numeric.out +++ b/src/test/regress/expected/numeric.out @@ -1333,6 +1333,33 @@ 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 -- diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql index 982287c33a..49ec478bd9 100644 --- a/src/test/regress/sql/numeric.sql +++ b/src/test/regress/sql/numeric.sql @@ -821,6 +821,18 @@ 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 --