netdev - Re: [PATCH net-next] net: ethernet: SP7021: fix a use after free of skb->len

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Message-ID: <CAFnkrsnR0LZRmZq0qAnhU9ysjYR2PAY15TmEHMt4EwdrD_AU-A@mail.gmail.com>
Date:   Thu, 19 May 2022 22:23:04 +0800
From:   呂芳騰 <wellslutw@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        netdev <netdev@...r.kernel.org>, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net-next] net: ethernet: SP7021: fix a use after free of skb->len

Hi Dan,

> The netif_receive_skb() function frees "skb" so store skb->len before
> it is freed.
>
> Fixes: fd3040b9394c ("net: ethernet: Add driver for Sunplus SP7021")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  drivers/net/ethernet/sunplus/spl2sw_int.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/sunplus/spl2sw_int.c b/drivers/net/ethernet/sunplus/spl2sw_int.c
> index 69b1e2e0271e..a37c9a4c281f 100644
> --- a/drivers/net/ethernet/sunplus/spl2sw_int.c
> +++ b/drivers/net/ethernet/sunplus/spl2sw_int.c
> @@ -29,6 +29,7 @@ int spl2sw_rx_poll(struct napi_struct *napi, int budget)
>         u32 mask;
>         int port;
>         u32 cmd;
> +       u32 len;
>
>         /* Process high-priority queue and then low-priority queue. */
>         for (queue = 0; queue < RX_DESC_QUEUE_NUM; queue++) {
> @@ -63,10 +64,11 @@ int spl2sw_rx_poll(struct napi_struct *napi, int budget)
>                         skb_put(skb, pkg_len - 4); /* Minus FCS */
>                         skb->ip_summed = CHECKSUM_NONE;
>                         skb->protocol = eth_type_trans(skb, comm->ndev[port]);
> +                       len = skb->len;
>                         netif_receive_skb(skb);
>
>                         stats->rx_packets++;
> -                       stats->rx_bytes += skb->len;
> +                       stats->rx_bytes += len;
>
>                         /* Allocate a new skb for receiving. */
>                         new_skb = netdev_alloc_skb(NULL, comm->rx_desc_buff_size);
> --
> 2.35.1
>

Thanks a lot for fixing the bug.

Can we just move the statement "stats->rx_bytes += skb->len;" to
before free skb?
For example,

skb_put(skb, pkg_len - 4); /* Minus FCS */
skb->ip_summed = CHECKSUM_NONE;
skb->protocol = eth_type_trans(skb, comm->ndev[port]);
stats->rx_packets++;
stats->rx_bytes += skb->len;
netif_receive_skb(skb);

/* Allocate a new skb for receiving. */
new_skb = netdev_alloc_skb(NULL, comm->rx_desc_buff_size);

Best regards,
Wells