linux-kernel - [PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL

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Message-Id: <20230801173544.1929519-6-hch@lst.de>
Date:   Tue,  1 Aug 2023 19:35:44 +0200
From:   Christoph Hellwig <hch@....de>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Manuel Lauss <manuel.lauss@...il.com>,
        Yangbo Lu <yangbo.lu@....com>, Joshua Kinard <kumba@...too.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org (open list),
        linux-mmc@...r.kernel.org, netdev@...r.kernel.org,
        linux-rtc@...r.kernel.org, linux-modules@...r.kernel.org
Subject: [PATCH 5/5] modules: only allow symbol_get of EXPORT_SYMBOL_GPL modules

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 proprietary
modules into an allegedly GPL licensed module and then rexporting them.

Given that symbol_get was only ever intended for tightly cooperating
modules using very internal symbols it is logical to restrict it to
being used on EXPORT_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@....de>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/module/main.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 59b1d067e52890..c395af9eced114 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1295,12 +1295,20 @@ void *__symbol_get(const char *symbol)
 	};
 
 	preempt_disable();
-	if (!find_symbol(&fsa) || strong_try_module_get(fsa.owner)) {
-		preempt_enable();
-		return NULL;
+	if (!find_symbol(&fsa))
+		goto fail;
+	if (fsa.license != GPL_ONLY) {
+		pr_warn("failing symbol_get of non-GPLONLY symbol %s.\n",
+			symbol);
+		goto fail;
 	}
+	if (strong_try_module_get(fsa.owner))
+		goto fail;
 	preempt_enable();
 	return (void *)kernel_symbol_value(fsa.sym);
+fail:
+	preempt_enable();
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(__symbol_get);
 
-- 
2.39.2