linux-kernel - [PATCH 3.16 053/148] staging: rtl8192e: fix potential use after free

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Message-ID: <lsq.1581185940.777280857@decadent.org.uk>
Date:   Sat, 08 Feb 2020 18:19:52 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Pan Bian" <bianpan2016@....com>
Subject: [PATCH 3.16 053/148] staging: rtl8192e: fix potential use after free

3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Pan Bian <bianpan2016@....com>

commit b7aa39a2ed0112d07fc277ebd24a08a7b2368ab9 upstream.

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>
Reviewed-by: Dan Carpenter <dan.carpenter@...cle.com>
Link: https://lore.kernel.org/r/1572965351-6745-1-git-send-email-bianpan2016@163.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/staging/rtl8192e/rtl8192e/rtl_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
+++ b/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
@@ -1884,8 +1884,6 @@ void rtl8192_hard_data_xmit(struct sk_bu
 	memcpy((unsigned char *)(skb->cb), &dev, sizeof(dev));
 	skb_push(skb, priv->rtllib->tx_headroom);
 	ret = rtl8192_tx(dev, skb);
-	if (ret != 0)
-		kfree_skb(skb);
 
 	if (queue_index != MGNT_QUEUE) {
 		priv->rtllib->stats.tx_bytes += (skb->len -
@@ -1893,6 +1891,9 @@ void rtl8192_hard_data_xmit(struct sk_bu
 		priv->rtllib->stats.tx_packets++;
 	}
 
+	if (ret != 0)
+		kfree_skb(skb);
+
 	return;
 }