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Fix unsafe order of operations in foreign-table DDL commands.

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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.
This commit is contained in:
Tom Lane 2011-08-14 15:40:36 -04:00
parent 739cbdd9c3
commit 5707f35559
1 changed files with 14 additions and 17 deletions
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31
src/backend/commands/foreigncmds.c
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@ -202,6 +202,8 @@ 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,
@ -218,8 +220,6 @@ 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))
@ -340,6 +340,8 @@ CreateForeignDataWrapper(CreateFdwStmt *stmt)
Datum fdwoptions;
Oid ownerId;
rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
/* Must be super user */
if (!superuser())
ereport(ERROR,
@ -363,8 +365,6 @@ 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));
@ -435,6 +435,8 @@ AlterForeignDataWrapper(AlterFdwStmt *stmt)
Datum datum;
Oid fdwvalidator;
rel = heap_open(ForeignDataWrapperRelationId, RowExclusiveLock);
/* Must be super user */
if (!superuser())
ereport(ERROR,
@ -513,9 +515,6 @@ 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);
@ -613,6 +612,8 @@ 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();
@ -638,8 +639,6 @@ CreateForeignServer(CreateForeignServerStmt *stmt)
/*
* Insert tuple into pg_foreign_server.
*/
rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
@ -714,6 +713,8 @@ AlterForeignServer(AlterForeignServerStmt *stmt)
Oid srvId;
Form_pg_foreign_server srvForm;
rel = heap_open(ForeignServerRelationId, RowExclusiveLock);
tp = SearchSysCacheCopy1(FOREIGNSERVERNAME,
CStringGetDatum(stmt->servername));
@ -779,9 +780,6 @@ 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);
@ -901,6 +899,8 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
ForeignServer *srv;
ForeignDataWrapper *fdw;
rel = heap_open(UserMappingRelationId, RowExclusiveLock);
useId = GetUserOidFromMapping(stmt->username, false);
/* Check that the server exists. */
@ -926,8 +926,6 @@ CreateUserMapping(CreateUserMappingStmt *stmt)
/*
* Insert tuple into pg_user_mapping.
*/
rel = heap_open(UserMappingRelationId, RowExclusiveLock);
memset(values, 0, sizeof(values));
memset(nulls, false, sizeof(nulls));
@ -986,6 +984,8 @@ AlterUserMapping(AlterUserMappingStmt *stmt)
Oid umId;
ForeignServer *srv;
rel = heap_open(UserMappingRelationId, RowExclusiveLock);
useId = GetUserOidFromMapping(stmt->username, false);
srv = GetForeignServerByName(stmt->servername, false);
@ -1043,9 +1043,6 @@ 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);