The skb->len field is read after the packet is sent to the network
stack. In the meantime, skb can be freed. This patch fixes this bug.

Fixes: c3e6b2c35b34 ("net: lantiq_xrx200: add ingress SG DMA support")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
---
 drivers/net/ethernet/lantiq_xrx200.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
index 41d11137cde0..5712c3e94be8 100644
--- a/drivers/net/ethernet/lantiq_xrx200.c
+++ b/drivers/net/ethernet/lantiq_xrx200.c
@@ -260,9 +260,9 @@ static int xrx200_hw_receive(struct xrx200_chan *ch)
 
 	if (ctl & LTQ_DMA_EOP) {
 		ch->skb_head->protocol = eth_type_trans(ch->skb_head, net_dev);
-		netif_receive_skb(ch->skb_head);
 		net_dev->stats.rx_packets++;
 		net_dev->stats.rx_bytes += ch->skb_head->len;
+		netif_receive_skb(ch->skb_head);
 		ch->skb_head = NULL;
 		ch->skb_tail = NULL;
 		ret = XRX200_DMA_PACKET_COMPLETE;
-- 
2.30.2

On 3/5/22 12:20, Aleksander Jan Bajkowski wrote:
> The skb->len field is read after the packet is sent to the network
> stack. In the meantime, skb can be freed. This patch fixes this bug.
> 
> Fixes: c3e6b2c35b34 ("net: lantiq_xrx200: add ingress SG DMA support")
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>

Acked-by: Hauke Mehrtens <hauke@hauke-m.de>

> ---
>   drivers/net/ethernet/lantiq_xrx200.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
> index 41d11137cde0..5712c3e94be8 100644
> --- a/drivers/net/ethernet/lantiq_xrx200.c
> +++ b/drivers/net/ethernet/lantiq_xrx200.c
> @@ -260,9 +260,9 @@ static int xrx200_hw_receive(struct xrx200_chan *ch)
>   
>   	if (ctl & LTQ_DMA_EOP) {
>   		ch->skb_head->protocol = eth_type_trans(ch->skb_head, net_dev);
> -		netif_receive_skb(ch->skb_head);
>   		net_dev->stats.rx_packets++;
>   		net_dev->stats.rx_bytes += ch->skb_head->len;
> +		netif_receive_skb(ch->skb_head);
>   		ch->skb_head = NULL;
>   		ch->skb_tail = NULL;
>   		ret = XRX200_DMA_PACKET_COMPLETE;

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Sat,  5 Mar 2022 12:20:39 +0100 you wrote:
> The skb->len field is read after the packet is sent to the network
> stack. In the meantime, skb can be freed. This patch fixes this bug.
> 
> Fixes: c3e6b2c35b34 ("net: lantiq_xrx200: add ingress SG DMA support")
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
> 
> [...]

Here is the summary with links:
  - [net] net: lantiq_xrx200: fix use after free bug
    https://git.kernel.org/netdev/net/c/dd830aed23c6

You are awesome, thank you!
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