postgres.git / summary / log / commit / refs
commit fe578cbd4b4262496d44cb5cd110eae3c4aff48c
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue Aug 08 23:18:12 2017 +0000
Fix datumSerialize infrastructure to not crash on non-varlena data.
Commit 1efc7e538 did a poor job of emulating existing logic for touching
Datums that might be expanded-object pointers. It didn't check for typlen
being -1 first, which meant it could crash on fixed-length pass-by-ref
values, and probably on cstring values as well. It also didn't use
DatumGetPointer before VARATT_IS_EXTERNAL_EXPANDED, which while currently
harmless is not according to documentation nor prevailing style.
I also think the lack of any explanation as to why datumSerialize makes
these particular nonobvious choices is pretty awful, so fix that.
Per report from Jarred Ward. Back-patch to 9.6 where this code came in.
Discussion: https://postgr.es/m/6F61E6D2-2F5E-4794-9479-A429BE1CEA4B@simple.com
src/backend/utils/adt/datum.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/src/backend/utils/adt/datum.c b/src/backend/utils/adt/datum.c
index c6c296b9609..d02e3c81106 100644
--- a/src/backend/utils/adt/datum.c
+++ b/src/backend/utils/adt/datum.c
@@ -264,11 +264,11 @@ datumEstimateSpace(Datum value, bool isnull, bool typByVal, int typLen)
/* no need to use add_size, can't overflow */
if (typByVal)
sz += sizeof(Datum);
- else if (VARATT_IS_EXTERNAL_EXPANDED(value))
+ else if (typLen == -1 &&
+ VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(value)))
{
- ExpandedObjectHeader *eoh = DatumGetEOHP(value);
-
- sz += EOH_get_flat_size(eoh);
+ /* Expanded objects need to be flattened, see comment below */
+ sz += EOH_get_flat_size(DatumGetEOHP(value));
}
else
sz += datumGetSize(value, typByVal, typLen);
@@ -282,6 +282,13 @@ datumEstimateSpace(Datum value, bool isnull, bool typByVal, int typLen)
*
* Serialize a possibly-NULL datum into caller-provided storage.
*
+ * Note: "expanded" objects are flattened so as to produce a self-contained
+ * representation, but other sorts of toast pointers are transferred as-is.
+ * This is because the intended use of this function is to pass the value
+ * to another process within the same database server. The other process
+ * could not access an "expanded" object within this process's memory, but
+ * we assume it can dereference the same TOAST pointers this one can.
+ *
* The format is as follows: first, we write a 4-byte header word, which
* is either the length of a pass-by-reference datum, -1 for a
* pass-by-value datum, or -2 for a NULL. If the value is NULL, nothing
@@ -306,7 +313,8 @@ datumSerialize(Datum value, bool isnull, bool typByVal, int typLen,
header = -2;
else if (typByVal)
header = -1;
- else if (VARATT_IS_EXTERNAL_EXPANDED(value))
+ else if (typLen == -1 &&
+ VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(value)))
{
eoh = DatumGetEOHP(value);
header = EOH_get_flat_size(eoh);
[parent: 1924ef416687]