[PATCH AUTOSEL 5.5 454/542] bcache: fix use-after-free in register_bcache()

[Sasha Levin]

From: Coly Li <colyli@xxxxxxx>

[ 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@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 bd2ae1d78fe15..05cb94664efee 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -2475,10 +2475,11 @@ 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