[PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL_GPL modules

[Christoph Hellwig <hch@lst.de>]

It has recently come to my attention that nvidia is circumventing the
protection added in 262e6ae7081d ("modules: inherit
TAINT_PROPRIETARY_MODULE") by importing exports from their propriertary
modules into an allegedly GPL licensed module and then rexporting them.

Given that symbol_get was only ever inteded for tightly cooperating
modules using very internal symbols it is logical to restrict it to
being used on EXPORY_SYMBOL_GPL and prevent nvidia from costly DMCA
circumvention of access controls law suites.

All symbols except for four used through symbol_get were already exported
as EXPORT_SYMBOL_GPL, and the remaining four ones were switched over in
the preparation patches.

Fixes: 262e6ae7081d ("modules: inherit TAINT_PROPRIETARY_MODULE")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 kernel/module/internal.h |  1 +
 kernel/module/main.c     | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index c8b7b4dcf7820d..add687c2abde8b 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -93,6 +93,7 @@ struct find_symbol_arg {
 	/* Input */
 	const char *name;
 	bool gplok;
+	bool gplonly;
 	bool warn;
 
 	/* Output */
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 59b1d067e52890..85d3f00ca65758 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -281,6 +281,8 @@ static bool find_exported_symbol_in_section(const struct symsearch *syms,
 
 	if (!fsa->gplok && syms->license == GPL_ONLY)
 		return false;
+	if (fsa->gplonly && syms->license != GPL_ONLY)
+		return false;
 
 	sym = bsearch(fsa->name, syms->start, syms->stop - syms->start,
 			sizeof(struct kernel_symbol), cmp_name);
@@ -776,8 +778,9 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 void __symbol_put(const char *symbol)
 {
 	struct find_symbol_arg fsa = {
-		.name	= symbol,
-		.gplok	= true,
+		.name		= symbol,
+		.gplok		= true,
+		.gplonly	= true,
 	};
 
 	preempt_disable();
@@ -1289,14 +1292,18 @@ static void free_module(struct module *mod)
 void *__symbol_get(const char *symbol)
 {
 	struct find_symbol_arg fsa = {
-		.name	= symbol,
-		.gplok	= true,
-		.warn	= true,
+		.name		= symbol,
+		.gplok		= true,
+		.gplonly	= true,
+		.warn		= true,
 	};
 
 	preempt_disable();
 	if (!find_symbol(&fsa) || strong_try_module_get(fsa.owner)) {
 		preempt_enable();
+		if (fsa.gplonly)
+			pr_warn("failing symbol_get of non-GPLONLY symbol %s.\n",
+				symbol);
 		return NULL;
 	}
 	preempt_enable();
-- 
2.39.2