v2-0001-Avoid-leaking-system-path-from-pg_available_exten.patch

From eaf271a14944df7df87601827f5f5e4909e38c33 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 v2] 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: Lu Feng <fnlo1995@gmail.com>
Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>
Discussion: https://postgr.es/m/357C774A-ECE9-4455-B641-315205D4D9A1@gmail.com
---
 src/backend/commands/extension.c                          | 8 +++++---
 .../test_extensions/t/001_extension_control_path.pl       | 6 +++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index a330b5fd6ce..d073585c421 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -513,6 +513,7 @@ is_extension_script_filename(const char *filename)
 static List *
 get_extension_control_directories(void)
 {
+#define EXTENSION_SYSTEM_MACRO  "$system"
 	char		sharepath[MAXPGPATH];
 	char	   *system_dir;
 	char	   *ecp;
@@ -526,7 +527,7 @@ get_extension_control_directories(void)
 	{
 		ExtensionLocation *location = palloc_object(ExtensionLocation);
 
-		location->macro = NULL;
+		location->macro = pstrdup(EXTENSION_SYSTEM_MACRO);
 		location->loc = system_dir;
 		paths = lappend(paths, location);
 	}
@@ -556,10 +557,10 @@ get_extension_control_directories(void)
 			 * Substitute the path macro if needed or append "extension"
 			 * suffix if it is a custom extension control path.
 			 */
-			if (strcmp(piece, "$system") == 0)
+			if (strcmp(piece, EXTENSION_SYSTEM_MACRO) == 0)
 			{
 				location->macro = pstrdup(piece);
-				mangled = substitute_path_macro(piece, "$system", system_dir);
+				mangled = substitute_path_macro(piece, EXTENSION_SYSTEM_MACRO, system_dir);
 			}
 			else
 			{
@@ -582,6 +583,7 @@ get_extension_control_directories(void)
 	}
 
 	return paths;
+#undef EXTENSION_SYSTEM_MACRO
 }
 
 /*
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)