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@163.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1572965351-6745-1-git-send-email-bianpan2016@163.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/rtl8192e/rtl8192e/rtl_core.c b/drivers/staging/rtl8192e/rtl8192e/rtl_core.c
index b08712a..dace81a 100644 (file)
--- 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)