From 1d49c888755b26d51fba03538ee2ce28478a86ad Mon Sep 17 00:00:00 2001 From: Tom Lane <tgl@sss.pgh.pa.us> Date: Sun, 11 Jul 2021 12:54:24 -0400 Subject: [PATCH] Lock the extension during ALTER EXTENSION ADD/DROP. Although we were careful to lock the object being added or dropped, we failed to get any sort of lock on the extension itself. This allowed the ALTER to proceed in parallel with a DROP EXTENSION, which is problematic for a couple of reasons. If both commands succeeded we'd be left with a dangling link in pg_depend, which would cause problems later. Also, if the ALTER failed for some reason, it might try to print the extension's name, and that could result in a crash or (in older branches) a silly error message complaining about extension "(null)". Per bug #17098 from Alexander Lakhin. Back-patch to all supported branches. Discussion: https://postgr.es/m/17098-b960f3616c861f83@postgresql.org --- src/backend/commands/extension.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c index 8e23c70fb36..9763c14f0ec 100644 --- a/src/backend/commands/extension.c +++ b/src/backend/commands/extension.c @@ -3196,9 +3196,17 @@ ExecAlterExtensionContentsStmt(AlterExtensionContentsStmt *stmt, Relation relation; Oid oldExtension; - extension.classId = ExtensionRelationId; - extension.objectId = get_extension_oid(stmt->extname, false); - extension.objectSubId = 0; + /* + * Find the extension and acquire a lock on it, to ensure it doesn't get + * dropped concurrently. A sharable lock seems sufficient: there's no + * reason not to allow other sorts of manipulations, such as add/drop of + * other objects, to occur concurrently. Concurrently adding/dropping the + * *same* object would be bad, but we prevent that by using a non-sharable + * lock on the individual object, below. + */ + extension = get_object_address(OBJECT_EXTENSION, + (Node *) makeString(stmt->extname), + &relation, AccessShareLock, false); /* Permission check: must own extension */ if (!pg_extension_ownercheck(extension.objectId, GetUserId())) -- 2.39.5