From:   Muchun Song <songmuchun@bytedance.com>
To:     glider@google.com, elver@google.com, dvyukov@google.com,
        akpm@linux-foundation.org, jannh@google.com, sjpark@amazon.de
Cc:     kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, muchun.song@linux.dev,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH] mm: kfence: fix using kfence_metadata without initialization in show_object()
Date:   Wed, 15 Mar 2023 11:44:41 +0800
Message-Id: <20230315034441.44321-1-songmuchun@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The variable kfence_metadata is initialized in kfence_init_pool(), then, it is
not initialized if kfence is disabled after booting. In this case, kfence_metadata
will be used (e.g. ->lock and ->state fields) without initialization when reading
/sys/kernel/debug/kfence/objects. There will be a warning if you enable
CONFIG_DEBUG_SPINLOCK. Fix it by creating debugfs files when necessary.

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/kfence/core.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 5349c37a5dac..79c94ee55f97 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -726,10 +726,14 @@ static const struct seq_operations objects_sops = {
 };
 DEFINE_SEQ_ATTRIBUTE(objects);
 
-static int __init kfence_debugfs_init(void)
+static int kfence_debugfs_init(void)
 {
-	struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL);
+	struct dentry *kfence_dir;
 
+	if (!READ_ONCE(kfence_enabled))
+		return 0;
+
+	kfence_dir = debugfs_create_dir("kfence", NULL);
 	debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);
 	debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
 	return 0;
@@ -883,6 +887,8 @@ static int kfence_init_late(void)
 	}
 
 	kfence_init_enable();
+	kfence_debugfs_init();
+
 	return 0;
 }
 
-- 
2.11.0