Subject: Re: [PATCH net 1/2] net: socionext: fix possible user-after-free in netsec_process_rx

From: Jesper Dangaard Brouer <[email-masked]>
Date: Sat, 25 Jan 2020 13:45:21 +0100

On Sat, 25 Jan 2020 12:48:50 +0100
Lorenzo Bianconi <[email-masked]> wrote:

> Fix possible use-after-free in in netsec_process_rx that can occurs if
> the first packet is sent to the normal networking stack and the
> following one is dropped by the bpf program attached to the xdp hook.
> Fix the issue defining the skb pointer in the 'budget' loop
> 
> Fixes: ba2b232108d3c ("net: netsec: add XDP support")
> Signed-off-by: Lorenzo Bianconi <[email-masked]>
> ---

Acked-by: Jesper Dangaard Brouer <[email-masked]>

>  drivers/net/ethernet/socionext/netsec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> index 869a498e3b5e..0e12a9856aea 100644
> --- a/drivers/net/ethernet/socionext/netsec.c
> +++ b/drivers/net/ethernet/socionext/netsec.c
> @@ -929,7 +929,6 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
>  	struct netsec_rx_pkt_info rx_info;
>  	enum dma_data_direction dma_dir;
>  	struct bpf_prog *xdp_prog;
> -	struct sk_buff *skb = NULL;
>  	u16 xdp_xmit = 0;
>  	u32 xdp_act = 0;
>  	int done = 0;
> @@ -943,6 +942,7 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
>  		struct netsec_de *de = dring->vaddr + (DESC_SZ * idx);
>  		struct netsec_desc *desc = &dring->desc[idx];
>  		struct page *page = virt_to_page(desc->addr);
> +		struct sk_buff *skb = NULL;
>  		u32 xdp_result = XDP_PASS;
>  		u16 pkt_len, desc_len;
>  		dma_addr_t dma_handle;

Yes, this is needed in case an xdp_prog jumps to label 'next:',
skipping the skb = build_skb() assignment.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer