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 eed0955793d7a1e0e62557076c0853d86e9ce7d0..b8baa63c4bc9a6b3b25d1acd414261203470bd51 100644 (file)
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -4840,9 +4840,15 @@ 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;
@@ -4857,7 +4863,7 @@ 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 5fafdaf13f5bd14ea41f21804e794dbe17a49abb..066e794192754f15c759b42b563e49ff06f00922 100644 (file)
--- a/src/test/regress/expected/numeric.out
+++ b/src/test/regress/expected/numeric.out
@@ -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
 --

diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
index 5c08717e7a968380af71ab4ecfaa7af6e2641477..f7e1bc9862e1a196b6b2aeb4c9faedfe1cf4da1b 100644 (file)
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -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
 --