netdev - Re: [PATCH net-next v2 5/6] tsnep: Add XDP socket zero-copy RX support

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Date:   Tue, 18 Apr 2023 20:41:59 +0200
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        bjorn@...nel.org, magnus.karlsson@...el.com,
        maciej.fijalkowski@...el.com, jonathan.lemon@...il.com
Subject: Re: [PATCH net-next v2 5/6] tsnep: Add XDP socket zero-copy RX
 support

On 18.04.23 10:22, Paolo Abeni wrote:
> On Sat, 2023-04-15 at 16:42 +0200, Gerhard Engleder wrote:
>> @@ -892,6 +900,37 @@ static int tsnep_rx_desc_available(struct tsnep_rx *rx)
>>   		return rx->read - rx->write - 1;
>>   }
>>   
>> +static void tsnep_rx_free_page_buffer(struct tsnep_rx *rx)
>> +{
>> +	struct page **page;
>> +
>> +	page = rx->page_buffer;
>> +	while (*page) {
>> +		page_pool_put_full_page(rx->page_pool, *page, false);
>> +		*page = NULL;
>> +		page++;
>> +	}
>> +}
> 
> [...]
> 
>>   static void tsnep_rx_close(struct tsnep_rx *rx)
>>   {
>> +	if (rx->xsk_pool)
>> +		tsnep_rx_free_page_buffer(rx);
> 
> It looks like the above could call tsnep_rx_free_page_buffer() with
> each page ptr in rx->page_buffer not zero. If so
> tsnep_rx_free_page_buffer() will do an out of bound access.

rx->page_buffer has space for up to TSNEP_RING_SIZE ptr's. The
descriptor ring is filled with at most TSNEP_RING_SIZE - 1
pages. Thus, the last ptr in rx->page_buffer is always zero.

> Also, why testing rx->xsk_pool instead of rx->page_buffer?

Testing for rx->xsk_pool is done for all code, which is only needed
if XSK zero-copy is enabled. For me this is more consistent to the
rest of the code.

Thanks!

Gerhard