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 a5dec22d9ca32c4e7851bd155755df66290ea260..2e61355f120102b94353580c688e20cd412d116b 100644 (file)
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -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;

diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.out
index 635c7d98408b20b29e6f17461bca3e7d5a3e2501..4abcb02d117a6e5ae1f95129846599ecad3452f3 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 1d380face20cb38bd9c55324ef39dc584b3bc1cd..fc1953601a17fb274d0fcb5dbaa389e9062d8813 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
 --