[PATCH 4.9 107/125] staging: rtl8192e: fix potential use after free

[Greg Kroah-Hartman]

From: Pan Bian <bianpan2016@xxxxxxx>

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@xxxxxxx>
Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1572965351-6745-1-git-send-email-bianpan2016@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -1630,14 +1630,15 @@ static void _rtl92e_hard_data_xmit(struc
 	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)