Subject: Re: [PATCH net] dpaa2-eth: Fix possible access beyond end of array

From: Jesper Dangaard Brouer <[email-masked]>
Date: Sun, 24 Mar 2019 19:28:52 +0100

On Wed, 20 Mar 2019 14:11:04 +0000
Ioana Ciocoi Radulescu <[email-masked]> wrote:

> Make sure we don't try to enqueue XDP_REDIRECT frames to an
> inexistent FQ.
> 
> While it is guaranteed not to have more than one queue per core,
> having fewer queues than CPUs on an interface is a valid
> configuration.
> 
> Fixes: d678be1dc1ec ("dpaa2-eth: add XDP_REDIRECT support")
> Reported-by: Jesper Dangaard Brouer <[email-masked]>
> Signed-off-by: Ioana Radulescu <[email-masked]>
> ---
>  drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> index 2ba49e9..1a68052 100644
> --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
> @@ -1817,7 +1817,7 @@ static int dpaa2_eth_xdp_xmit_frame(struct net_device *net_dev,
>  	dpaa2_fd_set_format(&fd, dpaa2_fd_single);
>  	dpaa2_fd_set_ctrl(&fd, FD_CTRL_PTA);
>  
> -	fq = &priv->fq[smp_processor_id()];
> +	fq = &priv->fq[smp_processor_id() % dpaa2_eth_queue_count(priv)];
>  	for (i = 0; i < DPAA2_ETH_ENQUEUE_RETRIES; i++) {
>  		err = priv->enqueue(priv, fq, &fd, 0);

Are you sure this is correct?
How do you guard/lock concurrent CPUs from accessing 'fq' ?

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