Fix subscriber invalid memory access on DDL.

This patch allows building the local relmap cache for a subscribed
relation after processing pending invalidation messages and potential
relcache updates.  Without this, the attributes in the local cache don't
tally with the updated relcache entry leading to invalid memory access.

Reported-by Jehan-Guillaume de Rorthais
Author: Jehan-Guillaume de Rorthais and Vignesh C
Reviewed-by: Amit Kapila
Backpatch-through: 10
Discussion: https://postgr.es/m/20191025175929.7e90dbf5@firost

diff --git a/src/backend/replication/logical/relation.c b/src/backend/replication/logical/relation.c
index aa59c455d4cdb10b1d4b8cd1f8641d29ef10d601..fa8489c6d43b5204df6da8d2a7553fdbe71f00b7 100644 (file)
--- a/src/backend/replication/logical/relation.c
+++ b/src/backend/replication/logical/relation.c
@@ -220,6 +220,8 @@ logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
 {
    LogicalRepRelMapEntry *entry;
    bool        found;
+   Oid         relid = InvalidOid;
+   LogicalRepRelation *remoterel;
 
    if (LogicalRepRelMap == NULL)
        logicalrep_relmap_init();
@@ -232,19 +234,16 @@ logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
        elog(ERROR, "no relation map entry for remote relation ID %u",
             remoteid);
 
-   /* Need to update the local cache? */
+   remoterel = &entry->remoterel;
+
+   /*
+    * When opening and locking a relation, pending invalidation messages are
+    * processed which can invalidate the relation.  We need to update the
+    * local cache both when we are first time accessing the relation and when
+    * the relation is invalidated (aka entry->localreloid is set InvalidOid).
+    */
    if (!OidIsValid(entry->localreloid))
    {
-       Oid         relid;
-       int         i;
-       int         found;
-       Bitmapset  *idkey;
-       TupleDesc   desc;
-       LogicalRepRelation *remoterel;
-       MemoryContext oldctx;
-
-       remoterel = &entry->remoterel;
-
        /* Try to find and lock the relation by name. */
        relid = RangeVarGetRelid(makeRangeVar(remoterel->nspname,
                                              remoterel->relname, -1),
@@ -256,6 +255,21 @@ logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
                            remoterel->nspname, remoterel->relname)));
        entry->localrel = heap_open(relid, NoLock);
 
+   }
+   else
+   {
+       relid = entry->localreloid;
+       entry->localrel = heap_open(entry->localreloid, lockmode);
+   }
+
+   if (!OidIsValid(entry->localreloid))
+   {
+       int         found;
+       Bitmapset  *idkey;
+       TupleDesc   desc;
+       MemoryContext oldctx;
+       int         i;
+
        /* Check for supported relkind. */
        CheckSubscriptionRelkind(entry->localrel->rd_rel->relkind,
                                 remoterel->nspname, remoterel->relname);
@@ -349,8 +363,6 @@ logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
 
        entry->localreloid = relid;
    }
-   else
-       entry->localrel = heap_open(entry->localreloid, lockmode);
 
    if (entry->state != SUBREL_STATE_READY)
        entry->state = GetSubscriptionRelState(MySubscription->oid,