linux-kernel - Re: [PATCH 5.10 26/76] sfc: Check null pointer of rx_queue->page

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Date:   Wed, 29 Dec 2021 12:17:30 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jiasheng Jiang <jiasheng@...as.ac.cn>,
        Martin Habets <habetsm.xilinx@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 26/76] sfc: Check null pointer of rx_queue->page_ring

hi!

> From: Jiasheng Jiang <jiasheng@...as.ac.cn>
> 
> [ Upstream commit bdf1b5c3884f6a0dc91b0dbdb8c3b7d205f449e0 ]
> 
> Because of the possible failure of the kcalloc, it should be better to
> set rx_queue->page_ptr_mask to 0 when it happens in order to maintain
> the consistency.

This is confusing/wrong, or at least not a complete fix.

> +++ 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 = 0;
> +	else
> +		rx_queue->page_ptr_mask = page_ring_size - 1;
>  }
>  

So we have !rx_queue->page_ring. But in efx_reuse_page, we do

        index = rx_queue->page_remove & rx_queue->page_ptr_mask;
	page = rx_queue->page_ring[index];

So index is now zero, but we'll derefernce null pointer anyway.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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