linux-kernel - [PATCH 1/2] module: Restrict module namespace access to in-tree modules

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Message-Id: <20250708-export_modules-v1-1-fbf7a282d23f@suse.cz>
Date: Tue, 08 Jul 2025 09:28:57 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Matthias Maennich <maennich@...gle.com>, 
 Jonathan Corbet <corbet@....net>, Luis Chamberlain <mcgrof@...nel.org>, 
 Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen <samitolvanen@...gle.com>, 
 Daniel Gomez <da.gomez@...sung.com>, Masahiro Yamada <masahiroy@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nicolas Schier <nicolas.schier@...ux.dev>, 
 Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: Christoph Hellwig <hch@...radead.org>, 
 Peter Zijlstra <peterz@...radead.org>, David Hildenbrand <david@...hat.com>, 
 Shivank Garg <shivankg@....com>, "Jiri Slaby (SUSE)" <jirislaby@...nel.org>, 
 Stephen Rothwell <sfr@...b.auug.org.au>, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
 linux-kbuild@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 1/2] module: Restrict module namespace access to in-tree
 modules

The module namespace support has been introduced to allow restricting
exports to specific modules only, and intended for in-tree modules such
as kvm. Make this intention explicit by disallowing out of tree modules
both for the module loader and modpost.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 Documentation/core-api/symbol-namespaces.rst | 5 +++--
 kernel/module/main.c                         | 3 ++-
 scripts/mod/modpost.c                        | 6 +++++-
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Documentation/core-api/symbol-namespaces.rst b/Documentation/core-api/symbol-namespaces.rst
index 32fc73dc5529e8844c2ce2580987155bcd13cd09..dc228ac738a5cdc49cc736c29170ca96df6a28dc 100644
--- a/Documentation/core-api/symbol-namespaces.rst
+++ b/Documentation/core-api/symbol-namespaces.rst
@@ -83,13 +83,14 @@ Symbols exported using this macro are put into a module namespace. This
 namespace cannot be imported.
 
 The macro takes a comma separated list of module names, allowing only those
-modules to access this symbol. Simple tail-globs are supported.
+modules to access this symbol. The access is restricted to in-tree modules.
+Simple tail-globs are supported.
 
 For example::
 
   EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*")
 
-will limit usage of this symbol to modules whoes name matches the given
+will limit usage of this symbol to in-tree modules whoes name matches the given
 patterns.
 
 How to use Symbols exported in Namespaces
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 413ac6ea37021bc8ae260f624ca2745ed85333fc..ec7d8daa0347e3b65713396d6b6d14c2cb0270d3 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1157,7 +1157,8 @@ static int verify_namespace_is_imported(const struct load_info *info,
 	namespace = kernel_symbol_namespace(sym);
 	if (namespace && namespace[0]) {
 
-		if (verify_module_namespace(namespace, mod->name))
+		if (get_modinfo(info, "intree") &&
+		    verify_module_namespace(namespace, mod->name))
 			return 0;
 
 		for_each_modinfo_entry(imported_namespace, info, "import_ns") {
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 5ca7c268294ebb65acb0ba52a671eddca9279c61..d78be9834ed75f4b6ddb9af02a300a9bcc9234cc 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1695,7 +1695,8 @@ void buf_write(struct buffer *buf, const char *s, int len)
  * @modname: module name
  *
  * If @namespace is prefixed with "module:" to indicate it is a module namespace
- * then test if @modname matches any of the comma separated patterns.
+ * then test if @modname matches any of the comma separated patterns. Access to
+ * module namespaces is restricted to in-tree modules only.
  *
  * The patterns only support tail-glob.
  */
@@ -1706,6 +1707,9 @@ static bool verify_module_namespace(const char *namespace, const char *modname)
 	const char *sep;
 	bool glob;
 
+	if (external_module)
+		return false;
+
 	if (!strstarts(namespace, prefix))
 		return false;
 

-- 
2.50.0