linux-kernel - [PATCH AUTOSEL 5.4 391/459] bcache: fix use-after-free in register

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Date:   Fri, 14 Feb 2020 11:00:41 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Coly Li <colyli@...e.de>, Christoph Hellwig <hch@....de>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-bcache@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 391/459] bcache: fix use-after-free in register_bcache()

From: Coly Li <colyli@...e.de>

[ Upstream commit ae3cd299919af6eb670d5af0bc9d7ba14086bd8e ]

The patch "bcache: rework error unwinding in register_bcache" introduces
a use-after-free regression in register_bcache(). Here are current code,
	2510 out_free_path:
	2511         kfree(path);
	2512 out_module_put:
	2513         module_put(THIS_MODULE);
	2514 out:
	2515         pr_info("error %s: %s", path, err);
	2516         return ret;
If some error happens and the above code path is executed, at line 2511
path is released, but referenced at line 2515. Then KASAN reports a use-
after-free error message.

This patch changes line 2515 in the following way to fix the problem,
	2515         pr_info("error %s: %s", path?path:"", err);

Signed-off-by: Coly Li <colyli@...e.de>
Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/bcache/super.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 86f7e09d31516..485ebc2b2144c 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -2472,10 +2472,11 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	kfree(sb);
 out_free_path:
 	kfree(path);
+	path = NULL;
 out_module_put:
 	module_put(THIS_MODULE);
 out:
-	pr_info("error %s: %s", path, err);
+	pr_info("error %s: %s", path?path:"", err);
 	return ret;
 }
 
-- 
2.20.1