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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jia-Ju Bai <baijiaju1990@gmail.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.20 217/352] cw1200: Fix concurrency use-after-free bugs in cw1200_hw_scan()
Date:   Mon, 11 Feb 2019 15:17:24 +0100
Message-Id: <20190211141901.036730955@linuxfoundation.org>
In-Reply-To: <20190211141846.543045703@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 4f68ef64cd7feb1220232bd8f501d8aad340a099 ]

The function cw1200_bss_info_changed() and cw1200_hw_scan() can be
concurrently executed.
The two functions both access a possible shared variable "frame.skb".

This shared variable is freed by dev_kfree_skb() in cw1200_upload_beacon(),
which is called by cw1200_bss_info_changed(). The free operation is
protected by a mutex lock "priv->conf_mutex" in cw1200_bss_info_changed().

In cw1200_hw_scan(), this shared variable is accessed without the
protection of the mutex lock "priv->conf_mutex".
Thus, concurrency use-after-free bugs may occur.

To fix these bugs, the original calls to mutex_lock(&priv->conf_mutex) and
mutex_unlock(&priv->conf_mutex) are moved to the places, which can
protect the accesses to the shared variable.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/wireless/st/cw1200/scan.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireless/st/cw1200/scan.c b/drivers/net/wireless/st/cw1200/scan.c
index 67213f11acbd..0a9eac93dd01 100644
--- a/drivers/net/wireless/st/cw1200/scan.c
+++ b/drivers/net/wireless/st/cw1200/scan.c
@@ -78,6 +78,10 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
 	if (req->n_ssids > WSM_SCAN_MAX_NUM_OF_SSIDS)
 		return -EINVAL;
 
+	/* will be unlocked in cw1200_scan_work() */
+	down(&priv->scan.lock);
+	mutex_lock(&priv->conf_mutex);
+
 	frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
 		req->ie_len);
 	if (!frame.skb)
@@ -86,19 +90,15 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
 	if (req->ie_len)
 		skb_put_data(frame.skb, req->ie, req->ie_len);
 
-	/* will be unlocked in cw1200_scan_work() */
-	down(&priv->scan.lock);
-	mutex_lock(&priv->conf_mutex);
-
 	ret = wsm_set_template_frame(priv, &frame);
 	if (!ret) {
 		/* Host want to be the probe responder. */
 		ret = wsm_set_probe_responder(priv, true);
 	}
 	if (ret) {
+		dev_kfree_skb(frame.skb);
 		mutex_unlock(&priv->conf_mutex);
 		up(&priv->scan.lock);
-		dev_kfree_skb(frame.skb);
 		return ret;
 	}
 
@@ -120,10 +120,9 @@ int cw1200_hw_scan(struct ieee80211_hw *hw,
 		++priv->scan.n_ssids;
 	}
 
-	mutex_unlock(&priv->conf_mutex);
-
 	if (frame.skb)
 		dev_kfree_skb(frame.skb);
+	mutex_unlock(&priv->conf_mutex);
 	queue_work(priv->workqueue, &priv->scan.work);
 	return 0;
 }
-- 
2.19.1