netdev - Re: [PATCH 1/1] ionic: fix array overflow on receiving too many fragments for a packet

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Date:   Sun, 6 Dec 2020 19:41:07 -0800
From:   Shannon Nelson <snelson@...sando.io>
To:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Xiaohui Zhang <ruc_zhangxiaohui@....com>
Cc:     Pensando Drivers <drivers@...sando.io>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ionic: fix array overflow on receiving too many
 fragments for a packet

On 12/6/20 5:51 PM, Jesse Brandeburg wrote:
> Xiaohui Zhang wrote:
>
>> From: Zhang Xiaohui <ruc_zhangxiaohui@....com>
>>
>> If the hardware receives an oversized packet with too many rx fragments,
>> skb_shinfo(skb)->frags can overflow and corrupt memory of adjacent pages.
>> This becomes especially visible if it corrupts the freelist pointer of
>> a slab page.
>>
>> Signed-off-by: Zhang Xiaohui <ruc_zhangxiaohui@....com>
> Hi, thanks for your patch.
>
> It appears this is a part of a series of patches (at least this one and
> one to the ice driver) - please send as one series, with a cover letter
> explanation.
>
> Please justify how this is a bug and how this is found / reproduced.
>
> I'll respond separately to the ice driver patch as I don't know this
> hardware and it's limits, but I suspect that you've tried to fix a bug
> where there was none. (It seems like something a code scanner might find
> and be confused about)
>
>> ---
>>   drivers/net/ethernet/pensando/ionic/ionic_txrx.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> index 169ac4f54..a3e274c65 100644
>> --- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> +++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
>> @@ -102,8 +102,12 @@ static struct sk_buff *ionic_rx_frags(struct ionic_queue *q,
>>   
>>   		dma_unmap_page(dev, dma_unmap_addr(page_info, dma_addr),
>>   			       PAGE_SIZE, DMA_FROM_DEVICE);
>> -		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
>> +		struct skb_shared_info *shinfo = skb_shinfo(skb);
> you can't declare variables in the middle of a code flow in C, did you
> compile this?
>
>> +
>> +		if (shinfo->nr_frags < ARRAY_SIZE(shinfo->frags)) {
>> +			skb_add_rx_frag(skb, shinfo->nr_frags,
>>   				page_info->page, 0, frag_len, PAGE_SIZE);
>> +		}

Is this just dropping the remaining frags without dropping the rest of 
the skb?  Is this going to leave an incorrect length in the skb?

A single statement after the 'if' doesn't need {}'s

This might be better handled by making sure ahead of time in 
configuration that the HW doesn't do this, rather than add a test into 
the fast path.  As it is, between the definitions of shinfo->frags[] and 
the ionic's rx sg list, I don't think this is a possible error.

As Jesse suggests, I'd like to see the test case so i can add it to our 
internal testing.

Thanks,
sln

>>   		page_info->page = NULL;
>>   		page_info++;
>>   		i--;
>