From 52994e9e5686b10a92bc93ec0f4e15c7fbc18242 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 14 Aug 2011 15:40:21 -0400
Subject: [PATCH] Fix unsafe order of operations in foreign-table DDL commands.
When updating or deleting a system catalog tuple, it's necessary to acquire
RowExclusiveLock on the catalog before looking up the tuple; otherwise a
concurrent VACUUM FULL on the catalog might move the tuple to a different
TID before we can apply the update. Coding patterns that find the tuple
via a table scan aren't at risk here, but when obtaining the tuple from a
catalog cache, correct ordering is important; and several routines in
foreigncmds.c got it wrong. Noted while running the regression tests in
parallel with VACUUM FULL of assorted system catalogs.
For consistency I moved all the heap_open calls to the starts of their
functions, including a couple for which there was no actual bug.
Back-patch to 8.4 where foreigncmds.c was added.
---
src/backend/commands/foreigncmds.c | 39 ++++++++++++++----------------
1 file changed, 18 insertions(+), 21 deletions(-)
diff --git a/src/backend/commands/foreigncmds.c b/src/backend/commands/foreigncmds.c
index d16932ba6a0..3a3c1313668 100644
--- a/src/backend/commands/foreigncmds.c
+++ b/src/backend/commands/foreigncmds.c
@@ -215,6 +215,8 @@ AlterForeignDataWrapperOwner(const char *name, Oid newOwnerId)
Oid fdwId;
Form_pg_foreign_data_wrapper form;
+ rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
+
/* Must be a superuser to change a FDW owner */
if (!superuser())
ereport(ERROR,
@@ -231,8 +233,6 @@ AlterForeignDataWrapperOwner(const char *name, Oid newOwnerId)
name),
errhint("The owner of a foreign-data wrapper must be a superuser.")));
- rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
-
tup = SearchSysCacheCopy1(FOREIGNDATAWRAPPERNAME, CStringGetDatum(name));
if (!HeapTupleIsValid(tup))
@@ -432,6 +432,8 @@ CreateForeignDataWrapper(CreateFdwStmt *stmt)
ObjectAddress myself;
ObjectAddress referenced;
+ rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
+
/* Must be super user */
if (!superuser())
ereport(ERROR,
@@ -455,8 +457,6 @@ CreateForeignDataWrapper(CreateFdwStmt *stmt)
/*
* Insert tuple into pg_foreign_data_wrapper.
*/
- rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
-
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
@@ -545,6 +545,8 @@ AlterForeignDataWrapper(AlterFdwStmt *stmt)
Oid fdwhandler;
Oid fdwvalidator;
+ rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
+
/* Must be super user */
if (!superuser())
ereport(ERROR,
@@ -635,9 +637,6 @@ AlterForeignDataWrapper(AlterFdwStmt *stmt)
}
/* Everything looks good - update the tuple */
-
- rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
-
tp = heap_modify_tuple(tp, RelationGetDescr(rel),
repl_val, repl_null, repl_repl);
@@ -773,6 +772,8 @@ CreateForeignServer(CreateForeignServerStmt *stmt)
ObjectAddress referenced;
ForeignDataWrapper *fdw;
+ rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
+
/* For now the owner cannot be specified on create. Use effective user ID. */
ownerId = GetUserId();
@@ -798,8 +799,6 @@ CreateForeignServer(CreateForeignServerStmt *stmt)
/*
* Insert tuple into pg_foreign_server.
*/
- rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
-
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
@@ -880,6 +879,8 @@ AlterForeignServer(AlterForeignServerStmt *stmt)
Oid srvId;
Form_pg_foreign_server srvForm;
+ rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
+
tp = SearchSysCacheCopy1(FOREIGNSERVERNAME,
CStringGetDatum(stmt->servername));
@@ -945,9 +946,6 @@ AlterForeignServer(AlterForeignServerStmt *stmt)
}
/* Everything looks good - update the tuple */
-
- rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
-
tp = heap_modify_tuple(tp, RelationGetDescr(rel),
repl_val, repl_null, repl_repl);
@@ -1068,6 +1066,8 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
ForeignServer *srv;
ForeignDataWrapper *fdw;
+ rel = heap_open(UserMappingRelationId, RowExclusiveLock);
+
useId = GetUserOidFromMapping(stmt->username, false);
/* Check that the server exists. */
@@ -1093,8 +1093,6 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
/*
* Insert tuple into pg_user_mapping.
*/
- rel = heap_open(UserMappingRelationId, RowExclusiveLock);
-
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
@@ -1161,6 +1159,8 @@ AlterUserMapping(AlterUserMappingStmt *stmt)
Oid umId;
ForeignServer *srv;
+ rel = heap_open(UserMappingRelationId, RowExclusiveLock);
+
useId = GetUserOidFromMapping(stmt->username, false);
srv = GetForeignServerByName(stmt->servername, false);
@@ -1218,9 +1218,6 @@ AlterUserMapping(AlterUserMappingStmt *stmt)
}
/* Everything looks good - update the tuple */
-
- rel = heap_open(UserMappingRelationId, RowExclusiveLock);
-
tp = heap_modify_tuple(tp, RelationGetDescr(rel),
repl_val, repl_null, repl_repl);
@@ -1344,11 +1341,13 @@ CreateForeignTable(CreateForeignTableStmt *stmt, Oid relid)
ForeignServer *server;
/*
- * Advance command counter to ensure the pg_attribute tuple visible; the
- * tuple might be updated to add constraints in previous step.
+ * Advance command counter to ensure the pg_attribute tuple is visible;
+ * the tuple might be updated to add constraints in previous step.
*/
CommandCounterIncrement();
+ ftrel = heap_open(ForeignTableRelationId, RowExclusiveLock);
+
/*
* For now the owner cannot be specified on create. Use effective user ID.
*/
@@ -1368,8 +1367,6 @@ CreateForeignTable(CreateForeignTableStmt *stmt, Oid relid)
/*
* Insert tuple into pg_foreign_table.
*/
- ftrel = heap_open(ForeignTableRelationId, RowExclusiveLock);
-
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
--
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