netdev - Re: [PATCH v4] sfc: potential dereference null pointer of rx_queue->page

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Date:   Mon, 20 Dec 2021 11:20:16 +0000
From:   Martin Habets <habetsm.xilinx@...il.com>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     ecree.xilinx@...il.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, kpsingh@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v4] sfc: potential dereference null pointer of
 rx_queue->page_ring

On Mon, Dec 20, 2021 at 10:37:15AM +0800, Jiasheng Jiang wrote:
> The return value of kcalloc() needs to be checked.

Maybe my previous reply against v2 crossed with your later versions.

Your predicate is wrong. The code that uses rx_queue->page_ring
can deal with it being NULL.
The only thing you might want to do is set rx_queue->page_ptr_mask
to 0.
It is a mask, never use a signed value for it.

Martin

> To avoid dereference of null pointer in case of the failure of alloc,
> such as efx_fini_rx_recycle_ring().
> Therefore, it should be better to change the definition of page_ptr_mask
> to signed int and then assign the page_ptr_mask to -1 when page_ring is
> NULL, in order to avoid the use in the loop.
> 
> Fixes: 5a6681e22c14 ("sfc: separate out SFC4000 ("Falcon") support into new sfc-falcon driver")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
> Changelog:
> 
> v3 -> v4
> 
> *Change 1. Casade return -ENOMEM when alloc fails and deal with the
> error.
> *Change 2. Set size to -1 instead of return error.
> *Change 3. Change the Fixes tag.
> ---
>  drivers/net/ethernet/sfc/net_driver.h | 2 +-
>  drivers/net/ethernet/sfc/rx_common.c  | 5 ++++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
> index 9b4b25704271..beba3e0a6027 100644
> --- a/drivers/net/ethernet/sfc/net_driver.h
> +++ b/drivers/net/ethernet/sfc/net_driver.h
> @@ -407,7 +407,7 @@ struct efx_rx_queue {
>  	unsigned int page_recycle_count;
>  	unsigned int page_recycle_failed;
>  	unsigned int page_recycle_full;
> -	unsigned int page_ptr_mask;
> +	int page_ptr_mask;
>  	unsigned int max_fill;
>  	unsigned int fast_fill_trigger;
>  	unsigned int min_fill;
> diff --git a/drivers/net/ethernet/sfc/rx_common.c b/drivers/net/ethernet/sfc/rx_common.c
> index 68fc7d317693..d9d0a5805f1c 100644
> --- a/drivers/net/ethernet/sfc/rx_common.c
> +++ b/drivers/net/ethernet/sfc/rx_common.c
> @@ -150,7 +150,10 @@ static void efx_init_rx_recycle_ring(struct efx_rx_queue *rx_queue)
>  					    efx->rx_bufs_per_page);
>  	rx_queue->page_ring = kcalloc(page_ring_size,
>  				      sizeof(*rx_queue->page_ring), GFP_KERNEL);
> -	rx_queue->page_ptr_mask = page_ring_size - 1;
> +	if (!rx_queue->page_ring)
> +		rx_queue->page_ptr_mask = -1;
> +	else
> +		rx_queue->page_ptr_mask = page_ring_size - 1;
>  }
>  
>  static void efx_fini_rx_recycle_ring(struct efx_rx_queue *rx_queue)
> -- 
> 2.25.1