linux-kernel - [PATCH 4.19 072/287] i2c: Fix a potential use after free

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Message-Id: <20220823080102.653454607@linuxfoundation.org>
Date:   Tue, 23 Aug 2022 10:24:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xu Wang <vulab@...as.ac.cn>,
        Wolfram Sang <wsa@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 072/287] i2c: Fix a potential use after free

From: Xu Wang <vulab@...as.ac.cn>

[ Upstream commit e4c72c06c367758a14f227c847f9d623f1994ecf ]

Free the adap structure only after we are done using it.
This patch just moves the put_device() down a bit to avoid the
use after free.

Fixes: 611e12ea0f12 ("i2c: core: manage i2c bus device refcount in i2c_[get|put]_adapter")
Signed-off-by: Xu Wang <vulab@...as.ac.cn>
[wsa: added comment to the code, added Fixes tag]
Signed-off-by: Wolfram Sang <wsa@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/i2c/i2c-core-base.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 2a43f4e46af0..9079be0d51d1 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -2273,8 +2273,9 @@ void i2c_put_adapter(struct i2c_adapter *adap)
 	if (!adap)
 		return;
 
-	put_device(&adap->dev);
 	module_put(adap->owner);
+	/* Should be last, otherwise we risk use-after-free with 'adap' */
+	put_device(&adap->dev);
 }
 EXPORT_SYMBOL(i2c_put_adapter);
 
-- 
2.35.1