v1-0001-Avoid-leaking-system-path-from-pg_available_exten.patch

From 0f9398b34a5484edbb93cb7771d6204bb37b6f7c Mon Sep 17 00:00:00 2001
From: "Chao Li (Evan)" <lic@highgo.com>
Date: Wed, 20 May 2026 08:49:15 +0800
Subject: [PATCH v1] Avoid leaking system path from pg_available_extensions

The documentation says that when extension_control_path is set to an
empty string, the default '$system' path is still assumed.  However,
get_extension_control_directories() added the system extension directory
with a NULL macro in that case.  As a result, pg_available_extensions
could expose the expanded system directory path instead of reporting
'$system' as the location.

Record the implicitly-added system directory with the '$system' macro, so
pg_available_extensions reports the documented symbolic location and does
not leak the actual system path.

Update the extension_control_path TAP test to check the reported location
directly.

Author: Chao Li <lic@highgo.com>
Reviewed-by:
Discussion: https://postgr.es/m/
---
 src/backend/commands/extension.c                            | 2 +-
 .../modules/test_extensions/t/001_extension_control_path.pl | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index a330b5fd6ce..98f9d7018ae 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -526,7 +526,7 @@ get_extension_control_directories(void)
 	{
 		ExtensionLocation *location = palloc_object(ExtensionLocation);
 
-		location->macro = NULL;
+		location->macro = pstrdup("$system");
 		location->loc = system_dir;
 		paths = lappend(paths, location);
 	}
diff --git a/src/test/modules/test_extensions/t/001_extension_control_path.pl b/src/test/modules/test_extensions/t/001_extension_control_path.pl
index c1cec0dc622..4a013a7da4b 100644
--- a/src/test/modules/test_extensions/t/001_extension_control_path.pl
+++ b/src/test/modules/test_extensions/t/001_extension_control_path.pl
@@ -109,10 +109,10 @@ is($ret, "t",
 	"\$system extension is shown correctly in pg_available_extensions");
 
 $ret = $node->safe_psql('postgres',
-	"set extension_control_path = ''; select count(*) > 0 as ok from pg_available_extensions where name = 'plpgsql'"
+	"set extension_control_path = ''; select location from pg_available_extensions where name = 'plpgsql'"
 );
-is($ret, "t",
-	"\$system extension is shown correctly in pg_available_extensions with empty extension_control_path"
+is($ret, "\$system",
+	"\$system location is shown correctly in pg_available_extensions with empty extension_control_path"
 );
 
 # Test with an extension that does not exists
-- 
2.50.1 (Apple Git-155)