Re: [PATCH] net: rswitch: Avoid use-after-free in rswitch_poll()

["Niklas Söderlund" <niklas.soderlund+renesas@ragnatech.se>]

Hi Radu,

On 2024-07-02 17:08:37 -0400, Radu Rendec wrote:
> The use-after-free is actually in rswitch_tx_free(), which is inlined in
> rswitch_poll(). Since `skb` and `gq->skbs[gq->dirty]` are in fact the
> same pointer, the skb is first freed using dev_kfree_skb_any(), then the
> value in skb->len is used to update the interface statistics.
> 
> Let's move around the instructions to use skb->len before the skb is
> freed.
> 
> This bug is trivial to reproduce using KFENCE. It will trigger a splat
> every few packets. A simple ARP request or ICMP echo request is enough.
> 
> Signed-off-by: Radu Rendec <rrendec@redhat.com>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

> ---
>  drivers/net/ethernet/renesas/rswitch.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
> index dcab638c57fe8..24c90d8f5a442 100644
> --- a/drivers/net/ethernet/renesas/rswitch.c
> +++ b/drivers/net/ethernet/renesas/rswitch.c
> @@ -871,13 +871,13 @@ static void rswitch_tx_free(struct net_device *ndev)
>  		dma_rmb();
>  		skb = gq->skbs[gq->dirty];
>  		if (skb) {
> +			rdev->ndev->stats.tx_packets++;
> +			rdev->ndev->stats.tx_bytes += skb->len;
>  			dma_unmap_single(ndev->dev.parent,
>  					 gq->unmap_addrs[gq->dirty],
>  					 skb->len, DMA_TO_DEVICE);
>  			dev_kfree_skb_any(gq->skbs[gq->dirty]);
>  			gq->skbs[gq->dirty] = NULL;
> -			rdev->ndev->stats.tx_packets++;
> -			rdev->ndev->stats.tx_bytes += skb->len;
>  		}
>  		desc->desc.die_dt = DT_EEMPTY;
>  	}
> -- 
> 2.45.2
> 

-- 
Kind Regards,
Niklas Söderlund