Re: BUG #18135: Incorrect memory access occurs when attaching a partition with an index

PG Bug reporting form <noreply@postgresql.org> writes:
> The function CompareIndexInfo() contains the code:
>         /* ignore expressions at this stage */
>         if ((info1->ii_IndexAttrNumbers[i] != InvalidAttrNumber) &&
>             (attmap->attnums[info2->ii_IndexAttrNumbers[i] - 1] !=
>              info1->ii_IndexAttrNumbers[i]))
>             return false;

> where info1->ii_IndexAttrNumbers[i] is checked for InvalidAttrNumber
> (i. e. it's not an expression), but info2->ii_IndexAttrNumbers[i] is not.

Agreed, that's pretty broken, and it's not just that it risks an
invalid access.  I don't think this reliably rejects cases where
one index has an expression and the other doesn't.  Even if it does
work, it's way too complicated to convince oneself that that's
rejected.  I think for clarity we should code it as attached.

            regards, tom lane

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 716de171a4..3d5adab2c5 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -2559,7 +2559,7 @@ CompareIndexInfo(const IndexInfo *info1, const IndexInfo *info2,

     /*
      * and columns match through the attribute map (actual attribute numbers
-     * might differ!)  Note that this implies that index columns that are
+     * might differ!)  Note that this checks that index columns that are
      * expressions appear in the same positions.  We will next compare the
      * expressions themselves.
      */
@@ -2568,13 +2568,22 @@ CompareIndexInfo(const IndexInfo *info1, const IndexInfo *info2,
         if (attmap->maplen < info2->ii_IndexAttrNumbers[i])
             elog(ERROR, "incorrect attribute map");

-        /* ignore expressions at this stage */
-        if ((info1->ii_IndexAttrNumbers[i] != InvalidAttrNumber) &&
-            (attmap->attnums[info2->ii_IndexAttrNumbers[i] - 1] !=
-             info1->ii_IndexAttrNumbers[i]))
-            return false;
+        /* ignore expressions for now (but check their collation/opfamily) */
+        if (!(info1->ii_IndexAttrNumbers[i] == InvalidAttrNumber &&
+              info2->ii_IndexAttrNumbers[i] == InvalidAttrNumber))
+        {
+            /* fail if just one index has an expression in this column */
+            if (info1->ii_IndexAttrNumbers[i] == InvalidAttrNumber ||
+                info2->ii_IndexAttrNumbers[i] == InvalidAttrNumber)
+                return false;
+
+            /* both are columns, so check for match after mapping */
+            if (attmap->attnums[info2->ii_IndexAttrNumbers[i] - 1] !=
+                info1->ii_IndexAttrNumbers[i])
+                return false;
+        }

-        /* collation and opfamily is not valid for including columns */
+        /* collation and opfamily are not valid for included columns */
         if (i >= info1->ii_NumIndexKeyAttrs)
             continue;