netdev - Re: [PATCH net-next] net: bcmgenet: Add a check for oversized packets

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Date:   Sun, 29 Jan 2023 13:17:43 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     netdev@...r.kernel.org, maxime@...no.tech,
        Doug Berger <opendmb@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: bcmgenet: Add a check for oversized packets



On 1/29/2023 1:42 AM, Leon Romanovsky wrote:
> On Thu, Jan 26, 2023 at 04:08:19PM -0800, Florian Fainelli wrote:
>> Occasionnaly we may get oversized packets from the hardware which
>> exceed the nomimal 2KiB buffer size we allocate SKBs with. Add an early
>> check which drops the packet to avoid invoking skb_over_panic() and move
>> on to processing the next packet.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>   drivers/net/ethernet/broadcom/genet/bcmgenet.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> index 21973046b12b..d937daa8ee88 100644
>> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> @@ -2316,6 +2316,14 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
>>   			  __func__, p_index, ring->c_index,
>>   			  ring->read_ptr, dma_length_status);
>>   
>> +		if (unlikely(len > RX_BUF_LENGTH)) {
>> +			netif_err(priv, rx_status, dev, "oversized packet\n");
> 
> I don't think that it is wise move to print to dmesg something that can
> be triggered by user over network.

A frame larger than RX_BUF_LENGTH intentionally received would be 
segmented by the MAC, we have seen this happen however while playing 
with unsafe clock ratios for instance or when there are insufficient 
credits given to the Ethernet MAC to write frames into DRAM. The print 
is consistent with other errors that are captured and is only enabled if 
the appropriate ethtool message level bitmask is set.
-- 
Florian