linux-kernel - [PATCH] staging: rtl8192e: fix potential use after free

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Message-Id: <1572965351-6745-1-git-send-email-bianpan2016@163.com>
Date:   Tue,  5 Nov 2019 22:49:11 +0800
From:   Pan Bian <bianpan2016@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Himadri Pandya <himadri18.07@...il.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Colin Ian King <colin.king@...onical.com>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Pan Bian <bianpan2016@....com>
Subject: [PATCH] staging: rtl8192e: fix potential use after free

The variable skb is released via kfree_skb() when the return value of
_rtl92e_tx is not zero. However, after that, skb is accessed again to
read its length, which may result in a use after free bug. This patch
fixes the bug by moving the release operation to where skb is never
used later.

Signed-off-by: Pan Bian <bianpan2016@....com>
---
 drivers/staging/rtl8192e/rtl8192e/rtl_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/rtl8192e/rtl8192e/rtl_core.c b/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
index f932cb15e4e5..cdcb22f96ed9 100644
--- a/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
+++ b/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
@@ -1616,14 +1616,15 @@ static void _rtl92e_hard_data_xmit(struct sk_buff *skb, struct net_device *dev,
 	memcpy((unsigned char *)(skb->cb), &dev, sizeof(dev));
 	skb_push(skb, priv->rtllib->tx_headroom);
 	ret = _rtl92e_tx(dev, skb);
-	if (ret != 0)
-		kfree_skb(skb);
 
 	if (queue_index != MGNT_QUEUE) {
 		priv->rtllib->stats.tx_bytes += (skb->len -
 						 priv->rtllib->tx_headroom);
 		priv->rtllib->stats.tx_packets++;
 	}
+
+	if (ret != 0)
+		kfree_skb(skb);
 }
 
 static int _rtl92e_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
-- 
2.7.4