[PATCH] net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

From: Lv Yunlong
Date: Mon Apr 26 2021 - 12:06:40 EST

In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..).
If some error happens in emac_tx_fill_tpd(), the skb will be freed via
dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd().
But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).

As i observed that emac_tx_fill_tpd() haven't modified the value of skb->len,
thus my patch assigns skb->len to 'len' before the possible free and
use 'len' instead of skb->len later.

Fixes: b9b17debc69d2 ("net: emac: emac gigabit ethernet controller driver")
Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
drivers/net/ethernet/qualcomm/emac/emac-mac.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/qualcomm/emac/emac-mac.c b/drivers/net/ethernet/qualcomm/emac/emac-mac.c
index 117188e3c7de..87b8c032195d 100644
--- a/drivers/net/ethernet/qualcomm/emac/emac-mac.c
+++ b/drivers/net/ethernet/qualcomm/emac/emac-mac.c
@@ -1437,6 +1437,7 @@ netdev_tx_t emac_mac_tx_buf_send(struct emac_adapter *adpt,
struct emac_tpd tpd;
u32 prod_idx;
+ int len;

memset(&tpd, 0, sizeof(tpd));

@@ -1456,9 +1457,10 @@ netdev_tx_t emac_mac_tx_buf_send(struct emac_adapter *adpt,
if (skb_network_offset(skb) != ETH_HLEN)
TPD_TYP_SET(&tpd, 1);

+ len = skb->len;
emac_tx_fill_tpd(adpt, tx_q, skb, &tpd);

- netdev_sent_queue(adpt->netdev, skb->len);
+ netdev_sent_queue(adpt->netdev, len);

/* Make sure the are enough free descriptors to hold one
* maximum-sized SKB. We need one desc for each fragment,