netdev - Re: [PATCH] sfc: potential dereference of null pointer

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Date:   Thu, 16 Dec 2021 20:19:42 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     ecree.xilinx@...il.com, habetsm.xilinx@...il.com,
        davem@...emloft.net, 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] sfc: potential dereference of null pointer

On Thu, 16 Dec 2021 16:49:02 +0800 Jiasheng Jiang wrote:
> [PATCH] sfc: potential dereference of null pointer

Please give the commit a more unique name.

> The return value of kcalloc() needs to be checked.
> 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 in
> efx_fini_rx_recycle_ring().

What about uses of this ring, you mention avoiding null-deref in the
freeing function but presumably something is actually using this ring
at runtime. Seems like we should return -ENOMEM.

> Fixes: 3d95b884392f ("sfc: move more rx code")

Moving buggy code does not introduce the problem, please find a Fixes
tag referring to where the bad code was _introduced_.

> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  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)